# The Official 1.8T forum turbo theory topic.



## iThread (Sep 27, 2005)

This topic is going to be specifically for debate about turbos, how they work, and the theory involved.
Hopefully hashing it all out here will keep the other topics free of the clutter this debate causes.
The rules will be strictly enforced here, especially the rules about personal attacks.


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## thom337 (Oct 13, 2007)

Do bigger turbos flow more volume of air through the engine? No.
Volumetric flow in an engine is controlled by engine displacement and RPM. The gains from a larger turbocharger come from its ability to flow air more efficiently. 
So, at the same RPM on the same engine, a k03 sport and GT-4088 are flowing the same VOLUME of air out of the compressor. 
Are they flowing the same mass of air? NO. 
Does volume flow have anything to do with performance by itself? NO!
Performance comes from mass flow of air, because it gives you the ability to burn more mass fuel and release more heat energy, which creates pressure, which creates force, which when acting over a distance creates torque, which at a speed creates power, etc etc etc.
Reading compressor maps for volume using pressure is not how its supposed to work. You are supposed to get your volume from the VOLUME FLOW of the engine, then you can use your boost pressure at that volume flow, combined with the compressor efficiency to calculate MASS flow.
_Modified by thom337 at 3:45 PM 8-27-2009_


_Modified by thom337 at 3:48 PM 8-27-2009_


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## Vegeta Gti (Feb 13, 2003)

*Re: (thom337)*

aaahahahahahahahahahahahahaha


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## 04VDubGLI (May 20, 2005)

I <3 Boost.
So... I'm confused as to what exactly is to be debated here? 
Are we trying to explain that compressor wheels are rated in lb/min (easily converted to CFM) or... what?


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## mescaline (Jul 15, 2005)

*Re: (thom337)*

A long time ago a man invented intercoolers to fix the density problems








I had no problems keeping my intake temperature down with K03S with very good intercooler so temperature is the same as GT28RS I have right now.
Density is a function of pressure and temperature, both are the same for both turbos meaning flowing in 100g/s of air with k03s and flowing 100g/s with GT28RS ...same **** ..it's the same air volume. Now with 
GT28RS you will flow more air mass, meaning you are flowing more volume as well


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## iThread (Sep 27, 2005)

*Re: (04VDubGLI)*


_Quote, originally posted by *04VDubGLI* »_Are we trying to explain that compressor wheels are rated in lb/min (easily converted to CFM) or... what? 

Anything and everything relating to turbos and how they function.
It's primarily so that people who want to debate about it can do it in here rather than in other topics.
Hopefully it works.


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## thom337 (Oct 13, 2007)

*Re: (04VDubGLI)*


_Quote, originally posted by *04VDubGLI* »_I <3 Boost.
So... I'm confused as to what exactly is to be debated here? 
Are we trying to explain that compressor wheels are rated in lb/min (easily converted to CFM) or... what? 

People were basically trying to say that bigger turbos push more volume flow into the engine, which is incorrect. The do suck in a greater volume at the compressor inlet, but at the compressor outlet the volume flow is dictated by the engine volumetric flowrate which is dictated by the engine speed and displacement.
Compressor maps are meant to be used at the compressor outlet...so the volume axes of the graph is dealing with how much volume the engine is flowing. Then, by using the working pressure ratio and efficiency, you can calculate mass flow which gives you a true idea of performance. CFM tells you very little about how much power the turbo will make without any density data.


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## Agtronic (May 14, 2001)

Let me get this going!
On a 1.8T motor, a K03S and a GT35R both set to 15 psi are flowing the same volume of air into the engine. (Not taking into account the increase in Volumetric Efficiency created by the larger hot side).


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## thom337 (Oct 13, 2007)

*Re: (mescaline)*


_Quote, originally posted by *mescaline* »_
Density is a function of pressure and temperature, both are the same for both turbos meaning flowing in 100g/s of air with k03s and flowing 100g/s with GT28RS ...same **** ..it's the same air volume. 

How is temperature the same for both turbos? The k03 charge will likely be less efficient, and therefore hotter. The GT28rs charge will be more efficient, and therefor colder, and denser. It is the same volume of air, with a different density, which results in a different mass flow, which results in different power output.

_Quote, originally posted by *mescaline* »_ 
Now with GT28RS you will flow more air mass, meaning you are flowing more volume as well









No...you cannot flow more volume than the engine has empty displacement space. If you are talking about compressor inlets, yes there is a great volume coming INTO the compressor (suction tube), but when its pumping at a pressure it is pumping the same volume INTO the engine as it would with any turbocharger.


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## mescaline (Jul 15, 2005)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
People were basically trying to say that bigger turbos push more volume flow into the engine, which is incorrect. The do suck in a greater volume at the compressor inlet, but at the compressor outlet the volume flow is dictated by the engine volumetric flowrate which is dictated by the engine speed and displacement.
Compressor maps are meant to be used at the compressor outlet...so the volume axes of the graph is dealing with how much volume the engine is flowing. Then, by using the working pressure ratio and efficiency, you can calculate mass flow which gives you a true idea of performance. CFM tells you very little about how much power the turbo will make without any density data.

Density of air changes all the time (mountains, sea level), this is why VW is using MAF and not...VAF ...lol, engine doesn't know what kind of IC you have either. 
Will bigger turbo flow more dense air? Probably, not necessarily...but is it making power on more dense air only? Not a chance, more dense air is responsible for 2% of extra power you get. More air inside the engine (and I mean volume) is responsible for everything else (AND APR OF COURSE)


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## Vegeta Gti (Feb 13, 2003)

*Re: (mescaline)*

this is so funny stuff.
MASS airflow sensor.


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## Agtronic (May 14, 2001)

*Re: (mescaline)*


_Quote, originally posted by *mescaline* »_More air inside the engine (and I mean volume) is responsible for everything else (AND APR OF COURSE) 

The part you are forgetting is that you cannot increase volume without increasing pressure, or decreasing restriction.
There are 2 reasons why larger turbos make more power :
1) The larger compressor is more efficient.
2) The turbine is less restrictive.


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## 04VDubGLI (May 20, 2005)

http://www.turbobygarrett.com/....html


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## thom337 (Oct 13, 2007)

*Re: (mescaline)*


_Quote, originally posted by *mescaline* »_
Density of air changes all the time (mountains, sea level), this is why VW is using MAF and not...VAF ...lol, engine doesn't know what kind of IC you have either. 



_Quote, originally posted by *mescaline* »_
Will bigger turbo flow more dense air? Probably, not necessarily...but is it making power on more dense air only? 

If it is the same volume, colder, and at the same pressure must it not also be more dense? YES.


_Quote, originally posted by *mescaline* »_
.but is it making power on more dense air only? Not a chance, more dense air is responsible for 2% of extra power you get. 

Power output is DIRECTLY proportional to charge density. If density is doubled, power output must double. Again, basic thermodynamics and physics.


_Quote, originally posted by *mescaline* »_
More air inside the engine (and I mean volume) is responsible for everything else (AND APR OF COURSE) 

There is not more volume of air in the engine with a larger compressor. The engine can only be filled until it is completely full, which is its volumetric capacity. Gains come from decreasing temperature and increasing pressure.


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## 04VDubGLI (May 20, 2005)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
There is not more volume of air in the engine with a larger compressor. The engine can only be filled until it is completely full, which is its volumetric capacity. Gains come from decreasing temperature and increasing pressure.


Volumetric Efficiency.
Density = Mass/Volume... Just something to keep in mind for everyone?


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## mescaline (Jul 15, 2005)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
If it is the same volume, colder, and at the same pressure must it not also be more dense? YES.


Why would it be colder? I said at the begining that I had 50C intake temperature with both turbos. Pressure is also the same.


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## thom337 (Oct 13, 2007)

*Re: (mescaline)*


_Quote, originally posted by *mescaline* »_
Why would it be colder? .

Compressor efficiency. Are we talking about turbos or intercoolers?


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## Agtronic (May 14, 2001)

*Re: (04VDubGLI)*


_Quote, originally posted by *04VDubGLI* »_http://www.turbobygarrett.com/....html

THank you, this proves the point rather well :

_Quote, originally posted by *TurboByGarrett.com* »_EXAMPLE:
I have an engine that I would like to use to make 400Hp, I want to choose an air/fuel ratio of 12 and use a BSFC of 0.55. Plugging these numbers into the formula from above:
of air.
Thus, a compressor map that has the capability of at least 44 pounds per minute of airflow capacity is a good starting point. 
Note that nowhere in this calculation did we enter any engine displacement or RPM numbers. This means that for any engine, in order to make 400 Hp, it needs to flow about 44 lb/min (this assumes that BSFC remains constant across all engine types).
*Naturally, a smaller displacement engine will require more boost or higher engine speed to meet this target than a larger engine will.* So how much boost pressure would be required?

The only way to get 44 lb/min into the motor is by increasing the boost.


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## mescaline (Jul 15, 2005)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
Compressor efficiency. Are we talking about turbos or intercoolers? 

Turbo or intercoolers? Are you saying if I add a good intercooler that will cool down K03S air to 40C and GT28RS is at 40C they will make the same power? That would be cheap heh.
I am telling you that intake temperature of both turbos were the same, 50C...this is logged...I have a log here somewhere, also both turbos were operating at 18 psi @ 4000 rpm. Now why would MAF report ~100g/s more for GT28RS if all parameters are the same?


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## mescaline (Jul 15, 2005)

*Re: (Agtronic)*


_Quote, originally posted by *Agtronic* »_
The only way to get 44 lb/min into the motor is by increasing the boost.

Wrong again, bigger turbo will get 44lb/min into engine at the same boost level as smaller turbo. 44lb/min which you can easily convert to CFM.


_Modified by mescaline at 1:22 PM 8-27-2009_


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## thom337 (Oct 13, 2007)

*Re: (mescaline)*


_Quote, originally posted by *mescaline* »_
Turbo or intercoolers? Are you saying if I add a good intercooler that will cool down K03S air to 40C and GT28RS is at 40C they will make the same power? That would be cheap heh.


That's exactly right. If you have a GT28RS making the same pressure and temperature at the same RPM as a K03, they will make exactly the same power. Now, cooling down a K03 that much and operating it reliably would be quite the task, but yes if you were able to do that they would make the same power and be flowing the same mass flow of air.


_Quote, originally posted by *mescaline* »_
I am telling you that intake temperature of both turbos were the same, 50C...this is logged...I have a log here somewhere, also both turbos were operating at 18 psi @ 4000 rpm. Now why would MAF report ~100g/s more for GT28RS if all parameters are the same?

It wouldn't. The situation you are describing is only possible if the IAT sensor is taking too long to register a temperature change. Try going steady state on a dyno at that same rpm and situation and then tell me the results. At the same manifold temperature, pressure, and RPM, the mass flowrates must be the same.


_Modified by thom337 at 4:30 PM 8-27-2009_


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## thom337 (Oct 13, 2007)

*Re: (mescaline)*


_Quote, originally posted by *mescaline* »_
Wrong again, bigger turbo will get 44lb/min into engine at the same boost level as smaller turbo.


Nope, it can do it at a lower boost level because the compressor exit temperatures won't be as high.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (mescaline)*

Let's interupt this ummm discussion to welcome our new moderator.. Welcome to the forum ithread







And no.. I'm not being sarcastic..


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## mescaline (Jul 15, 2005)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
That's exactly right. If you have a GT28RS making the same pressure and temperature at the same RPM as a K03, they will make exactly the same power. Now, cooling down a K03 that much and operating it reliably would be quite the task, but yes if you were able to do that they would make the same power and be flowing the same mass flow of air.


This is just...dumb.
I told you that I had 50C intake temperatures with K03S and with GT28RS, 18 psi @ 4000rpm. This is not faulty IAT sensor, ask around...lots of people have 50C intake temperatures with K03S...this is nothing unusual.
Bigger turbo can't double the air density man.
Anyway am going for a run, lots of dense air outside... i will burn off this fat i gained over vacation tonight ha ha 


_Modified by iThread at 1:37 PM 8-27-2009_


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## dubchuck117 (Feb 6, 2009)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
There is not more volume of air in the engine with a larger compressor. *The engine can only be filled until it is completely full, which is its volumetric capacity.* Gains come from decreasing temperature and increasing pressure.


the way a turbo works is by effectively cramming air into an engine, increasing its volumetric effeciency. this is why a gt28 at the same psi as a k03 will undoubtely make more power, because it is a) lowering charge temps and b) forcing more air into the engine. by your logic a bigger turbo just decreases charge temps and increases density. this makes sense to a point. but as you get into bigger turbos the temps arent going to change much more but cfm's are going to go up. its all about efficient volume http://****************.com/smile/emthup.gif


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## thom337 (Oct 13, 2007)

*Re: (mescaline)*


_Quote, originally posted by *mescaline* »_
This is just...dumb.
I told you that I had 50C intake temperatures with K03S and with GT28RS, 18 psi @ 4000rpm. This is not faulty IAT sensor, ask around...lots of people have 50C intake temperatures with K03S...this is nothing unusual.
Bigger turbo can't double the air density man, what the hell is wrong with you... two working brain cells would figure this out.
Anyway am going for a run, lots of dense air outside... i will burn off this fat i gained over vacation tonight ha ha 

I did not say the IAT sensor was "faulty". However, they are not meant to respond to rapid changes in temperature. You need a nice data logging setup and a good thermocouple. That is why I suggested doing a steady state pull at the same boost on a dyno, then you will see the temperature changes between the two turbos. Unless you have a holy intercooler core from the pope, your temperatures in the manifold for a K03s and a GT28rs at the same pressure and RPM will NOT be the same...and if they were, your mass flow would be the same.


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## mescaline (Jul 15, 2005)

*Re: (dubchuck117)*


_Quote, originally posted by *dubchuck117* »_
the way a turbo works is by effectively cramming air into an engine, increasing its volumetric effeciency. this is why a gt28 at the same psi as a k03 will undoubtely make more power, because it is a) lowering charge temps and b) forcing more air into the engine. by your logic a bigger turbo just decreases charge temps and increases density. this makes sense to a point. but as you get into bigger turbos the temps arent going to change much more but cfm's are going to go up. its all about efficient volume http://****************.com/smile/emthup.gif 

x2


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## [email protected] (Oct 23, 2008)

*Re: (dubchuck117)*

I think the confusion is one is ignoring the turbocharger and the other the engine. A larger turbo in the same engine will be much closer to the surge line then a smaller turbo on the map at a given boost. If left, unrestricted, it will flow more air, volume, mass whatever per revolution. PSI is whats built up in the charge piping as this is FORCED induction. If you have a free flowing event, nothing is forced. Both parties are correct to a certain degree. But the efficiency of a 35R at 15psi is much more so then the k03. Its taking less revolutions to do so and consuming less energy...


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## mescaline (Jul 15, 2005)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
I did not say the IAT sensor was "faulty". However, they are not meant to respond to rapid changes in temperature. You need a nice data logging setup and a good thermocouple. That is why I suggested doing a steady state pull at the same boost on a dyno, then you will see the temperature changes between the two turbos. Unless you have a holy intercooler core from the pope, your temperatures in the manifold for a K03s and a GT28rs at the same pressure and RPM will NOT be the same...and if they were, your mass flow would be the same. 

Even there is 40C or 100C difference in temperature, it won't affect density so much to double the power. With k03s I had stock IC before and I was pushing some insane boost levels, like 1.5bar or so...I logged IAT to like 90C, then I got bigger IC, it got temperature down to 50C ...guess what, power of engine didn't double...I gained maybe 5whp ...if that, but I had cooler engine. Your theory about air density is certainly there, but as said before...it's responsible for making 2% of extra power you get with bigger turbo.


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## thom337 (Oct 13, 2007)

*Re: (dubchuck117)*


_Quote, originally posted by *dubchuck117* »_
the way a turbo works is by effectively cramming air into an engine, increasing its volumetric effeciency. this is why a gt28 at the same psi as a k03 will undoubtely make more power, because it is a) lowering charge temps and b) forcing more air into the engine. by your logic a bigger turbo just decreases charge temps and increases density. this makes sense to a point. but as you get into bigger turbos the temps arent going to change much more but cfm's are going to go up. its all about efficient volume http://****************.com/smile/emthup.gif 

How can you fill something more than 100%? A turbo doesn't not keep filling something that is full, it causes a pressure rise which increases the DENSITY of the air in the engine. Turbos are all about CHARGE DENSITY. 
In regard to volumetric efficiency, I have seen some people regard turbos as simply increasing the volumetric efficiency beyond 100%. However, it then becomes somewhat of a mis-nomer as it doesn't make sense to fill something beyond 100%. Its better to describe it as 100% full, but with a higher density. The only time I see +100% VE used is when calculations are being made using atmospheric density in which case this makes sense.


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## [email protected] (Oct 23, 2008)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
How can you fill something more than 100%? A turbo doesn't not keep filling something that is full, it causes a pressure rise which increases the DENSITY of the air in the engine. Turbos are all about CHARGE DENSITY. 
In regard to volumetric efficiency, I have seen some people regard turbos as simply increasing the volumetric efficiency beyond 100%. However, it then becomes somewhat of a mis-nomer as it doesn't make sense to fill something beyond 100%. Its better to describe it as 100% full, but with a higher density. The only time I see +100% VE used is when calculations are being made using atmospheric density in which case this makes sense.

You can, its called surge as its pushing past the turbo..


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## mescaline (Jul 15, 2005)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_I think the confusion is one is ignoring the turbocharger and the other the engine. A larger turbo in the same engine will be much closer to the surge line then a smaller turbo on the map at a given boost. If left, unrestricted, it will flow more air, volume, mass whatever per revolution. PSI is whats built up in the charge piping as this is FORCED induction. If you have a free flowing event, nothing is forced. Both parties are correct to a certain degree. But the efficiency of a 35R at 15psi is much more so then the k03. Its taking less revolutions to do so and consuming less energy...

All thom and agtronics are saying is that K03S and GT28RS are flowing same amount (VOLUME) of air inside the engine...and I say bigger turbo is flowing more air inside the engine (lets forget what happens inside the engine and stuffing all that air inside the cylinder, no one is arguing this...you can't put 1000000 cf of air inside 1800cc engine. We are talking turbos here.


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## thom337 (Oct 13, 2007)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
You can, its called surge as its pushing past the turbo..

just talking about general turbo flowing into engine here, yes its possible to cause surge / backflow / compressor reversion but thats not really in scope of what we're talking about here.


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## [email protected] (Oct 23, 2008)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
just talking about general turbo flowing into engine here, yes its possible to cause surge / backflow / compressor reversion but thats not really in scope of what we're talking about here.

You cant talk about diff turbo sizes and not talk about that on the same engine..


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## mescaline (Jul 15, 2005)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
How can you fill something more than 100%? A turbo doesn't not keep filling something that is full, it causes a pressure rise which increases the DENSITY of the air in the engine. Turbos are all about CHARGE DENSITY. 
In regard to volumetric efficiency, I have seen some people regard turbos as simply increasing the volumetric efficiency beyond 100%. However, it then becomes somewhat of a mis-nomer as it doesn't make sense to fill something beyond 100%. Its better to describe it as 100% full, but with a higher density. The only time I see +100% VE used is when calculations are being made using atmospheric density in which case this makes sense.

Volumetric efficiency (VE) is used to describe the amount of fuel/air in the cylinder in relation to regular atmospheric air. If the cylinder is filled with fuel/air at atmospheric pressure, then the engine is said to have 100% volumetric efficiency. On the other hand, super chargers and turbo chargers increase the pressure entering the cylinder, giving the engine a volumetric efficiency greater than 100%.


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## Agtronic (May 14, 2001)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_I think the confusion is one is ignoring the turbocharger and the other the engine. A larger turbo in the same engine will be much closer to the surge line then a smaller turbo on the map at a given boost. If left, unrestricted, it will flow more air, volume, mass whatever per revolution. PSI is whats built up in the charge piping as this is FORCED induction. If you have a free flowing event, nothing is forced. Both parties are correct to a certain degree. But the efficiency of a 35R at 15psi is much more so then the k03. Its taking less revolutions to do so and consuming less energy...

This is exactly what we're trying to say. You said it exactly, IF LEFT UNRESTRICTED, naturally the larger turbo will flow more volume, but in the context of feeding a closed engine environment, where pressure is building, the same volume of air will make its way into the motor.


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## thom337 (Oct 13, 2007)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
You cant talk about diff turbo sizes and not talk about that on the same engine..

We're discussing the role of volume flow at the compressor outlet on performance. I'm saying that big turbos don't make more power because they flow more volume, but because they flow the same volume at a lower temperature and generally a higher pressure. I'm saying what is important is mass flow, not volume flow.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (thom337)*

The air is not being compressed into a sealed chamber. The pistons are moving the whole time, the air is being burned along with the fuel creating a less dense gas that is being forced out of the exhaust ports. Another thing. The charge air temperature can be regulated via water meth injection to a very low temp. Even if the air is coming out of a searing hot ko3s, it is possible to bring the air back down to close to ambient temperature.. If your theory was correct a k03s at 20 psi would make the same power as a 30r at 20psi... They don't make the same power no matter the density or the temperature because the volume is not there.. Again.. Garden hose / Fire hose


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## thom337 (Oct 13, 2007)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_ If your theory was correct a k03s at 20 psi would make the same power as a 30r at 20psi... . 

They will, at the same RPM and if they have the same exit temperature.


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## thom337 (Oct 13, 2007)

*Re: (thom337)*









That is how power is made, period. The rho term in the m_dot air equation is density. It is directly related to power output.
I should note that these equations are for a 4 stroke engine, and the mass values would be per second.
Also, efficiency is the thermodynamic efficiency of the engine. This isn't the compressor efficiency.
_Modified by thom337 at 5:01 PM 8-27-2009_

_Modified by thom337 at 5:01 PM 8-27-2009_


_Modified by thom337 at 5:04 PM 8-27-2009_


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## The*Fall*Guy (Aug 10, 2009)

*Re: (thom337)*

No they won't.. There are plenty of dyno charts showing the power of small turbos made with low iat temps via water meth.. They do not make the same power as a larger turbo with the same iat temps...


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## Agtronic (May 14, 2001)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_Again.. Garden hose / Fire hose









The garden hose / fire hose analogy does not work for a motor because a motor has a restrictor (head, valves, timing etc ...) If there was no restriction, pressure would never build (boost).
To make the Fire hose / Garden hose analogy work, you need to put a large lid on the swimming pool, with a 1/4" inlet, and set both hoses at the same pressure. Which hose will fill the pool faster if it has to push through the 1/4" inlet? Both will fill it at the same rate, if the same amount of pressure is building in the hose.


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## thom337 (Oct 13, 2007)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_No they won't.. There are plenty of dyno charts showing the power of small turbos made with low iat temps via water meth.. They do not make the same power as a larger turbo with the same iat temps... 

But are the IAT temps THE SAME. Is the pressure the EXACT SAME at the EXACT SAME RPMS? No. 
If you move the same mass of air with two different turbos, you get the same power. Period. You are wrong. Sir Harry Ricardo is rolling over in his grave right now at this ridiculousness.


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## mescaline (Jul 15, 2005)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
But are the IAT temps THE SAME. Is the pressure the EXACT SAME at the EXACT SAME RPMS? No. 


YES, they are.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_








That is how power is made, period. The rho term in the m_dot air equation is density. It is directly related to power output.
I should note that these equations are for a 4 stroke engine, and the mass values would be per second.
Also, efficiency is the thermodynamic efficiency of the engine. This isn't the compressor efficiency.
_Modified by thom337 at 5:01 PM 8-27-2009_

_Modified by thom337 at 5:01 PM 8-27-2009_

_Modified by thom337 at 5:04 PM 8-27-2009_
 Your little equation that you posted is correct. But you are not.. I know how power is made. You are trying to argue the efficiency of a turbo.. Yet are posting an equation showing how the efficiency of the engine itself dictates power.. Relevant.. But it doesn't prove your point.


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## thom337 (Oct 13, 2007)

*Re: (mescaline)*


_Quote, originally posted by *mescaline* »_

YES, they are.

Please, provide data for me where two turbos flow the same volume of air at the same temperature and pressure, but the mass flow is different. Do you understand what volume is? Do you understand what mass is? Can you perform basic multiplication and division?


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## Agtronic (May 14, 2001)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_No they won't.. There are plenty of dyno charts showing the power of small turbos made with low iat temps via water meth.. They do not make the same power as a larger turbo with the same iat temps... 

No, 'cause the turbine on the larger turbo is allowing the engine to take in more air at the given boost level.


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## thom337 (Oct 13, 2007)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_ Your little equation that you posted is correct. But you are not.. I know how power is made. You are trying to argue the efficiency of a turbo.. Yet are posting an equation showing how the efficiency of the engine itself dictates power.. Relevant.. But it doesn't prove your point.

Once again you miss the point. The efficiency I posted was for the engine, yes. I was making a general equation for power output. I wasn't trying to use the fact that all engines have efficiency to back up my previous statements.
What you missed: COMPRESSOR efficiency determines the rho (density) term in the m_dot air equation. Then that cylces down to the others. You can see how air charge density is directly proportional to power output.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
Please, provide data for me where two turbos flow the same volume of air at the same temperature and pressure, but the mass flow is different. Do you understand what volume is? Do you understand what mass is? Can you perform basic multiplication and division?
 I have an idea.. Why don't you dig up a few dyno charts proving your point.. After all your the one who believes he has superior intelligence.. If this is true the dyno charts to prove what you say should be all over.. Dyno numbers, and trap speeds don't lie.. People do..


----------



## BoostinBejan (Apr 13, 2009)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
They will, at the same RPM and if they have the same exit temperature.

Bingo. This guy is right. There's no reason me explaining it, becuase you are already trying to and it's not working..


----------



## BoostinBejan (Apr 13, 2009)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_ I have an idea.. Why don't you dig up a few dyno charts proving your point.. After all your the one who believes he has superior intelligence.. If this is true the dyno charts to prove what you say should be all over.. Dyno numbers, and trap speeds don't lie.. People do..

Think of it this way.
k03 at 15psi at 2000rpm on an engine.
GT30R at 15psi at 2000rpm on an engine.
same temp, same volume to fill, same engine, SAME POWER. The reason why you don't SEE that, is the fact that the k03 is falling off up top where the engine is most effecient, and the 30R keeps pushing.
edit- the engine doesn't know that it's a k03, or a 30r. As long as its pushing the same PSI through the intercooler piping, at the same RPM and same temperature, then you will have the exact same power.



_Modified by BoostinBejan at 2:18 PM 8-27-2009_


----------



## coreyj (Aug 18, 2006)

*Re: (thom337)*

sorry guys didnt mean to start a 2 page argument. lol


----------



## thom337 (Oct 13, 2007)

*Re: (BoostinBejan)*


_Quote, originally posted by *BoostinBejan* »_
Bingo. This guy is right. There's no reason me explaining it, becuase you are already trying to and it's not working..


I'm giving up, I've wasted a few hours trying to correct misinformation on the forum, but people would rather keep clinging to the incorrect way they've been doing things.


----------



## BoostinBejan (Apr 13, 2009)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
I'm giving up, I've wasted a few hours trying to correct misinformation on the forum, but people would rather keep clinging to the incorrect way they've been doing things.









that's the forum for you. 
FACEPALM ALL DAY.


----------



## The*Fall*Guy (Aug 10, 2009)

*Re: (BoostinBejan)*


_Quote, originally posted by *BoostinBejan* »_
Think of it this way.
k03 at 15psi at 2000rpm on an engine.
GT30R at 15psi at 2000rpm on an engine.
same temp, same volume to fill, same engine, SAME POWER. The reason why you don't SEE that, is the fact that the k03 is falling off up top where the engine is most effecient, and the 30R keeps pushing.
edit- the engine doesn't know that it's a k03, or a 30r. As long as its pushing the same PSI through the intercooler piping, at the same RPM and same temperature, then you will have the exact same power.
_Modified by BoostinBejan at 2:18 PM 8-27-2009_
 Bad example Bejan. Try proving that a 30r will make the Same power as a ko3s at 5000 rpm.. Its not gonna happen. Even if the charge temps are the same. Fire hose / Garden hose.


----------



## BoostinBejan (Apr 13, 2009)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_ Bad example Bejan. Try proving that a 30r will make the Same power as a ko3s at 5000 rpm.. Its not gonna happen. Even if the charge temps are the same. Fire hose / Garden hose.

at 5psi it sure will make the same power. a k03 cant make more then that efficiently. It's a perfect example.
edit- at 5000 rpm a k03 is effecient at 5psi, you will see the exactly same power as a 30R at 5000 rpm at 5psi. Guarantee it. Its physics.


_Modified by BoostinBejan at 2:30 PM 8-27-2009_


----------



## thom337 (Oct 13, 2007)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_ Bad example Bejan. Try proving that a 30r will make the Same power as a ko3s at 5000 rpm.. Its not gonna happen. Even if the charge temps are the same. Fire hose / Garden hose.

Why can't it happen? Because the K03 can't provide the boost pressure that a 30r can at 5,000rpm without choking the inlet or failing due to excessive shaft speed. If charge temps and pressure are the same at the same engine operating point the mass flow will be the same. The same power will then be created by the same mass flow conditions.


----------



## The*Fall*Guy (Aug 10, 2009)

*Re: (BoostinBejan)*

No its not.. Add water/meth to bring the charge temps down.. All is equal now. The efficiency has been bandaged by the water/ meth.. They still won't make the same power.


----------



## BoostinBejan (Apr 13, 2009)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_No its not.. Add water/meth to bring the charge temps down.. All is equal now. The efficiency has been bandaged by the water/ meth.. They still won't make the same power.

So what do you want to do, a test at 20psi at 5000 rpm? THERE IS A PROBLEM WITH THAT. a k03 cannot physically flow 20psi at 5000 rpm. Which is why I said 5psi.


----------



## thom337 (Oct 13, 2007)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_No its not.. Add water/meth to bring the charge temps down.. All is equal now. The efficiency has been bandaged by the water/ meth.. They still won't make the same power.

How is it equal now? How did you get the K03 to produce the same manifold pressure as the GT35 or 4088 or whatever? You must have the same a)temperature b) pressure c)engine and operating point. But at that point, you will have the same power.


----------



## BoostinBejan (Apr 13, 2009)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
How is it equal now? How did you get the K03 to produce the same manifold pressure as the GT35 or 4088 or whatever? You must have the same a)temperature b) pressure c)engine and operating point. But at that point, you will have the same power.

Ding ding ding!
It's pretty obvious that a k03 cannot flow the same amount of boost at the rpm range that the engine is effecient. like I said a hundred times, at 5000 rpms, the max the k03 can effecinelty flow is lets say 8PSI. Now with a GT35R with 8psi at 5000 rpm, it will make the exact same power since temp will be the same. How is that so hard to understand?


----------



## The*Fall*Guy (Aug 10, 2009)

*Re: (BoostinBejan)*

Bejan... Its not the boost pressure. Its the volume of air at a given boost pressure.. This is the argument I'm making.. These guys are trying to say that boost pressure is boost pressure. That as long as the temps are the same the power will be the same.. This is not true. The larger turbo will flow a bigger volume of air at the same temp and psi of a smaller turbo.. Bigger turbo at a given boost pressure = more volume at said pressure.. Garden hose/ fire hose..


----------



## BoostinBejan (Apr 13, 2009)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_Bejan... Its not the boost pressure. Its the volume of air at a given boost pressure.. This is the argument I'm making.. These guys are trying to say that boost pressure is boost pressure. That as long as the temps are the same the power will be the same.. This is not true. The larger turbo will flow a bigger volume of air at the same temp and psi of a smaller turbo.. Bigger turbo at a given boost pressure = more volume at said pressure.. Garden hose/ fire hose..

It doesn't matter. Your intercooler piping, intercooler, intake manifold, and combustion chamber is all staying the same.
I gaurentee that if you dyno a 1.8t with a k03 at 8psi, then dyno a GT30R at 8psi with the same engine/IC/everything. At 5000 rpm if they are both at 8psi, the power will be exactly the same.
Edit- I agree with these "Guys". BOOST PRESSURE IS BOOST PRESSURE. What you don't seem to be grasping is the fact that larger turbos can flow the same boost pressure at higher RPM. go look at a dyno, you make power at higher rpm for a reason. your engine is pumping faster. If you have a turbo that can keep up with how fast your engine is pumping, then you will make more power, period.


_Modified by BoostinBejan at 2:44 PM 8-27-2009_


----------



## Agtronic (May 14, 2001)

*Re: (BoostinBejan)*

Let's not forget another reason you will never see it, the K03 has a tiny little turbine that chokes the motor. If you fitted both compressors to the same turbine, they would make very similar numbers, until the K03 fell out of its efficiency range (which doesn't take much). And without having the compressor maps in front of me, the K03 is likely more efficient at low boost / flow levels than the 35R.
The whole point of this thread is this :
In simple terms, the larger turbo is NOT FLOWING MORE volume at the same boost level, it is simply feeding a DENSER charge into the engine, and letting it out easier on the exhaust side. It's really that simple.
edit : added the word "volume" to avoid further confusion.


_Modified by Agtronic at 4:05 PM 8-29-2009_


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## The*Fall*Guy (Aug 10, 2009)

*Re: (BoostinBejan)*


_Quote, originally posted by *BoostinBejan* »_

Edit- I agree with these "Guys". BOOST PRESSURE IS BOOST PRESSURE. What you don't seem to be grasping is the fact that larger turbos can flow the same boost pressure at higher RPM. go look at a dyno, you make power at higher rpm for a reason. your engine is pumping faster. If you have a turbo that can keep up with how fast your engine is pumping, then you will make more power, period.

_Modified by BoostinBejan at 2:44 PM 8-27-2009_
 don't patronise me Bejan... I understand how turbos make power, and why a bigger turbo makes more power at a higher rpm.. I'm not stupid, and you know this. If you re-read everything these guys have said word for word, you will see the contradictions in their statements, and their mincing of words.


----------



## thom337 (Oct 13, 2007)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_ If you re-read everything these guys have said word for word, you will see the contradictions in their statements, and their mincing of words. 

What about straight physics equations that say you are wrong?







What do you have to say about those? A volume flow at a given temperature and pressure is a MASS FLOW. It doesn't matter what turbo it comes out of, it will make the same power.


----------



## Agtronic (May 14, 2001)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_ don't patronise me Bejan... I understand how turbos make power, and why a bigger turbo makes more power at a higher rpm.. I'm not stupid, and you know this. If you re-read everything these guys have said word for word, you will see the contradictions in their statements, and their mincing of words. 

Okay, so you're saying that bolting on a physically larger compressor will flow more air into the same motor at the same RPM using the same pressure level? If so, it's physically impossible, and I don't think any analogy will make you guys understand this. You cannot argue with the laws of physics. 
You simply CANNOT flow more air volume into a restricted space. The only way you can flow more air MASS into this restricted space, is if you decrease the temperature, or increase the pressure. *
If you cannot accept this, then there is no arguing.
* EDIT : Corrected wording for clarity.


_Modified by Agtronic at 4:28 PM 8-29-2009_


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## The*Fall*Guy (Aug 10, 2009)

*Re: (Agtronic)*

Good point. But its not a confined space. The pistons are moving, combustion is taking place, and the variables are changing every millisecond. These theory's may work on paper, but in reality they don't cut it. I'm outta here.. It was fun raising our collective blood pressures


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## BoostinBejan (Apr 13, 2009)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_Good point. But its not a confined space. The pistons are moving, combustion is taking place, and the variables are changing every millisecond. These theory's may work on paper, but in reality they don't cut it. I'm outta here.. It was fun raising our collective blood pressures









Leaving won't make you win. it is a confined space. It's the same space that the k03 would be pushing through, that is what matters. the piping pressurizes the same way with a larger or smaller turbo.


----------



## catsman72 (Mar 14, 2008)

*Re: (The*Fall*Guy)*

Well my theory about turbos all started when I had to go poop one day when I was about 14 and my brother was 16....... and well we I was doing my thang and I started thinking what if we put a fan on my brothers engine (Honda d16y7) to make it go fasters. well we did put a dam ebay t3 on that sucker @ 10psi after I got off the toilet of course, and it has lasted two years and still to this day has no shaft play doggy dog!
Well after two years or so I gots my jet jetta and he was like god dam it batman I'm building my engine and putting a bigger fan on its and I also want some dam VTEC to!!!!!!!! so we gots that bigger fan (Holset hy35) and then we slapped that bitch on there @ 24psi and batman was like OMFG Robbin I need help *******. the end. 
as said turbo hondaer


----------



## Agtronic (May 14, 2001)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_Good point. But its not a confined space. The pistons are moving, combustion is taking place, and the variables are changing every millisecond. These theory's may work on paper, but in reality they don't cut it. I'm outta here.. It was fun raising our collective blood pressures









It isn't a confined space, but at a given RPM, the restriction remains the same. 
I still want a GT35R to replace my 50 TRIM!


----------



## 16plus4v (May 4, 2006)

*Re: (Agtronic)*


_Quote, originally posted by *Agtronic* »_In simple terms, the larger turbo is NOT FLOWING MORE at the same boost level, it is simply feeding a DENSER charge into the engine, and letting it out easier on the exhaust side. It's really that simple.


Couldn't be more simple.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (BoostinBejan)*

Wasn't trying to win... There is no point in winning anything on here. Its a forum meant to share ideas, and maybe bicker a little bit. And to this guy who just posted.. grow up.. I'm not some idiot who thinks he's gonna makes mad powaz yo.. I could say more about this fella who just posted, but since we now have a moderator ill behave. And bid this thread farewell.. Again


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## BoostinBejan (Apr 13, 2009)

*Re: (The*Fall*Guy)*

i PM'd you ^^


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## Bryan on Boost (Aug 8, 2009)

You know fellas, if you want to argue the two turbos' power output at same rpm, boost, and temp, you must also consider the other side of the engine and turbo as well. There will inevitably be a difference in exhaust restriction between the two turbos, affecting flow and also load of the engine. Difficult to get the EXACT same power from two different turbos for these reasons. Interesting topic, I hope no one is having a heart attack right now. Keep it friendly fellas!


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## BoostinBejan (Apr 13, 2009)

*Re: (Bryan on Boost)*

Markku and I both agreed that our blood was boiling over this for no reason. shouldn't let forum talk get to me, but sometimes it does... you are absolutely right though, there is less restriction on the larger turbo, but at low boost it would not create too much of a problem for a test.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (BoostinBejan)*

Its no biggie.. These are the type of "discussions" that keep this forum alive.. At least it isn't another dv vs bov thread


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## 50trim S (Jun 3, 2008)

*FV-QR*

i would like to see a dyno of a k03 and 35r at say 12 psi to redline and im PRETTY sure the 35r will make more power even if you make in intake temps the same
if you disagree, prove it
plain and simple because im on the straw and hose theory if thats what you want to call it .


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## Bryan on Boost (Aug 8, 2009)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_.. At least it isn't another dv vs bov thread
















No doubt, this does have more technical bearing


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## 50trim S (Jun 3, 2008)

*Re: (Agtronic)*


_Quote, originally posted by *Agtronic* »_
It isn't a confined space, but at a given RPM, the restriction remains the same. 
I still want a GT35R to replace my 50 TRIM!









why according to you and that other guy they both will make the same power if the IAT are the same?
you contradicting yourself


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## The*Fall*Guy (Aug 10, 2009)

*Re: (Bryan on Boost)*

Exactly... I've been working on dubs for well over ten yrs and this forum is great. If there's a disagreement.. Who cares? Within all of the fighting is always some great knowledge if you know where to look.. Some guys bring up valid points.. Some guys post formulas that they googled to make themselves look smart.. When in reality the posted formula is only loosely related to the discussion at best... At the end of the day we all learn something, or get a bad case of heartburn.. Either way something has been accomplished... I love this forum


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## 04VDubGLI (May 20, 2005)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
Why can't it happen? Because the K03 can't provide the boost pressure that a 30r can at 5,000rpm without choking the inlet or failing due to excessive shaft speed. If charge temps and pressure are the same at the same engine operating point the mass flow will be the same. *The same power will then be created by the same mass flow conditions.*

I've bolded the only portion of what you just said that makes sense/matters. Whenever turbo A (whatever you want to make it) flows 100 g/s across a MAF and turbo B flows 100 g/s across the same MAF then they are going to be REALLY close in power. Now you can insert assumptions about temps. What you keep misposting about is it doesn't matter what PSI turbo A is making or what PSI turbo B is making (now, ignoring pressure ratios is not correct, but let's assume both are within the same level of efficiency - call it a Bullseye S256 and 3076 if it makes you feel better). The important thing here is that they are both flowing 100 g/s (temp, blah blah blah = the same b/c of IC). Now, if turbo A needs 100psi to flow 100 g/s and turbo B uses 50psi to flow 100 g/s it's irrelevant to the amount of power being generated. 
Honestly, the garden hose thing and fire hose thing isn't exactly far off... I can see the argument brewing here though. If you attach a garden SIZED hose to a fire hydrant then you get the correct correlation.


----------



## Agtronic (May 14, 2001)

*Re: (50trim S)*


_Quote, originally posted by *50trim S* »_why according to you and that other guy they both will make the same power if the IAT are the same?
you contradicting yourself























I never said they would make the same power. A K03 turbine is much more restrictive than a 35R turbine. 
Listen guys, I was not trying to come in here act all knowing and stuff, I was just trying to clear up a misconception that I see often on the internet. I don't think anyone is dumb or stupid for not getting it ... Knowing the reasons behind the turbo choices we make doesn't really change anything in the real world, except that the next time you build a turbo car, you might not need to rely on what everyone before you has done, and may be better able to choose a turbo, cam or whatever based on what you know the motor will do.


----------



## Agtronic (May 14, 2001)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_Exactly... I've been working on dubs for well over ten yrs and this forum is great. If there's a disagreement.. Who cares? Within all of the fighting is always some great knowledge if you know where to look.. Some guys bring up valid points.. Some guys post formulas that they googled to make themselves look smart.. When in reality the posted formula is only loosely related to the discussion at best... At the end of the day we all learn something, or get a bad case of heartburn.. Either way something has been accomplished... I love this forum









Agreed, I don't make posts to "win", I make posts to help people understand things that took me a while to understand. When people start calling me names and saying that they can't believe I run a shop, then it gets under my skin a little, especially when I'm only trying to help clear things up ... But meh, that's the internet for ya!


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## The*Fall*Guy (Aug 10, 2009)

*Re: (Agtronic)*

I know how to read a compressor map. This argument turned into more of a mincing of words than anything.. But as I said. This was a productive argument. Although the points you were arguing were more true on paper than they ever could be in the real world.. As I said a dozen times. Show me two radicaly different sized turbos make the same power at the same boost pressure.. Even under ideal conditions its not going to happen..


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## Agtronic (May 14, 2001)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_As I said a dozen times. Show me two radicaly different sized turbos make the same power at the same boost pressure.. Even under ideal conditions its not going to happen..
 
And I said they won't. It's not going to happen, and we all know this. My point, from the beginning, was that the reason they won't make the same power is not because the compressor is "flowing more" air at the same boost.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (Agtronic)*

Fine


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## 20aeman (Jun 8, 2006)

comparing a 28rs to a k03s is apples and oranges. If you can cool the intake charge from a K03s, it will make comparable numbers to a 28rs at a given boost pressure on a specific point in the rev range. AT A GIVEN BOOST PRESSURE ON A SPECIFIC POINT IN THE REV RANGE. The boost on a ko3s tapers due to the ****ty hotside...think low 20s down to the single digits @ redline. Pick one point...say 6500rpm..where the ko3s is maxed out at 9 psi (with an intercooler the size of a suitcase and water/meth)....swap a gt28rs, set the boost at 9 psi...the numbers will be comparable.


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## coreyj (Aug 18, 2006)

haha between this thread and the other its 5 pages of arguing in 1 day.


_Modified by coreyj at 9:21 PM 8-27-2009_


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## dubchuck117 (Feb 6, 2009)

*Re: (20aeman)*

wow i leave for a couple hours an three pages lol
it seems this thread got waay off point, iirc the arguement was temperatures vs. volume for turbo power. i see people are throwing in lag times and stuff and thats not what it was about. put it this way, if you had an engine with one k04 at 17 psi (well in its efficiency range) and another identical engine with TWO at the same psi, which is going to make more power? the temps wouldnt be any higher because all three turbos are running the same psi, therefore the same level of efficiency correct? but naturally the one with two turbos is making mor power. why? more air


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## BoostinBejan (Apr 13, 2009)

*Re: (dubchuck117)*


_Quote, originally posted by *dubchuck117* »_wow i leave for a couple hours an three pages lol
it seems this thread got waay off point, iirc the arguement was temperatures vs. volume for turbo power. i see people are throwing in lag times and stuff and thats not what it was about. put it this way, if you had an engine with one k04 at 17 psi (well in its efficiency range) and another identical engine with TWO at the same psi, which is going to make more power? the temps wouldnt be any higher because all three turbos are running the same psi, therefore the same level of efficiency correct? but naturally the one with two turbos is making mor power. why? more air









Wrong.
Same amount of air. If you have a set volume (IC piping, same engine, etc) and same pressure (17psi) then you have the same amount of "air". Not more air. That is completly wrong.
The reason why the car with 2 turbos would make more power, assuming the same psi under the same RPM range, is becuase there is far less backpressure do to the exhaust flowing through 2 turbine housings instead of one. Not only that but lets say 2 turbos would have to flow 8-9psi to equal one flowing 17psi, the 2 turbos flowing 8-9psi would be flowing much cooler/denser air and therefore those 2 reasons is why it would make more power, nothing to do with "Boost" or "flowing more air".
Make sense?


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## 20aeman (Jun 8, 2006)

*Re: (dubchuck117)*


_Quote, originally posted by *dubchuck117* »_wow i leave for a couple hours an three pages lol
it seems this thread got waay off point, iirc the arguement was temperatures vs. volume for turbo power. i see people are throwing in lag times and stuff and thats not what it was about. put it this way, if you had an engine with one k04 at 17 psi (well in its efficiency range) and another identical engine with TWO at the same psi, which is going to make more power? the temps wouldnt be any higher because all three turbos are running the same psi, therefore the same level of efficiency correct? but naturally the one with two turbos is making mor power. why? more air









Ummmmm NO. I'm officially ignoring this thread.








I didn't know everyone had such a loose grasp on physics.


_Modified by 20aeman at 6:58 PM 8-27-2009_


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## dubchuck117 (Feb 6, 2009)

wait....
thougt about it...
thats a fail on my behalf....
but i still maintain volume has more effect on power than temps


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## Agtronic (May 14, 2001)

*Re: (BoostinBejan)*


_Quote, originally posted by *BoostinBejan* »_The reason why the car with 2 turbos would make more power, assuming the same psi under the same RPM range, is becuase there is far less backpressure do to the exhaust flowing through 2 turbine housings instead of one. Not only that but lets say 2 turbos would have to flow 8-9psi to equal one flowing 17psi, the 2 turbos flowing 8-9psi would be flowing much cooler/denser air and therefore those 2 reasons is why it would make more power, nothing to do with "Boost" or "flowing more air".

Technically, both turbos would both be boosting to 17 psi, but the flow volume would be shared between both turbos, so they would only have to work half as hard to maintain the boost.

_Quote, originally posted by *dubchuck117* »_wait....
thougt about it...
thats a fail on my behalf....
but i still maintain volume has more effect on power than temps

Yes, if you increase the volume, you will increase the power. The whole point of this thread is that you can only increase volume by increasing pressure. If the pressure stays the same (15 psi), there will always be the same volume going into the motor. The only thing that changes with the larger turbo is the density of that volume, and the engine's VE because of the larger turbine.


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## Agtronic (May 14, 2001)

*Re: (coreyj)*


_Quote, originally posted by *coreyj* »_haha between this thread and the other its 5 pages of arguing in 1 day.

I feel like an ass now, I usually hate people who try and correct others on the internet. That was not my intention, at all!


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## 04VDubGLI (May 20, 2005)

*Re: (Agtronic)*


_Quote, originally posted by *Agtronic* »_
Technically, both turbos would both be boosting to 17 psi, but the flow volume would be shared between both turbos, so they would only have to work half as hard to maintain the boost.
Yes, if you increase the volume, you will increase the power. The whole point of this thread is that you can only increase volume by increasing pressure. If the pressure stays the same (15 psi), there will always be the same volume going into the motor. The only thing that changes with the larger turbo is the density of that volume, and the engine's VE because of the larger turbine.

How about we move on to discuss billet wheeled turbos then. Let's look at the HTA 3582 and regular 3582?
How about an explanation for why the BILLET 3582 makes more power than the regular 3582? Same turbine wheel... same turbine housing... same dimensions. Same car. Why does it make more power?








I guess I better get 4 k03s and make individual manifolds and run them all at 40psi. By far the best option. Oh, maybe I should get a huge turbine housing for each of those 4 as well. No matter what the compressor wheels STILL ARE RATED FOR LIKE 25 LB/MIN. Why is this such a difficult concept? They can only move so much air, period.


_Modified by 04VDubGLI at 11:02 PM 8-27-2009_


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## 20aeman (Jun 8, 2006)

*Re: (04VDubGLI)*


_Quote, originally posted by *04VDubGLI* »_
How about we move on to discuss billet wheeled turbos then. Let's look at the HTA 3582 and regular 3582?
How about an explanation for why the BILLET 3582 makes more power than the regular 3582? Same turbine wheel... same turbine housing... same dimensions. Same car. Why does it make more power?








I guess I better get 4 k03s and make individual manifolds and run them all at 40psi. By far the best option. Oh, maybe I should get a huge turbine housing for each of those 4 as well. No matter what the compressor wheels STILL ARE RATED FOR LIKE 25 LB/MIN. Why is this such a difficult concept? They can only move so much air, period.

_Modified by 04VDubGLI at 11:02 PM 8-27-2009_

It doesn't make more peak power from the pic you just posted, regardless, the billet wheel turbos have slightly different compressor maps, and are simply more efficient due to the decrease in the weight of the compressor.


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## NOLA_VDubber (May 24, 2007)

*Re: (04VDubGLI)*

this thread needs more T-s diagrams


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## 04VDubGLI (May 20, 2005)

*Re: (NOLA_VDubber)*


_Quote, originally posted by *NOLA_VDubber* »_this thread needs more T-s diagrams

Thought about copy + pasting some over... but decided against








This link is very relevant to this discussion as far as I'm concerned.
http://forums.vwvortex.com/zer...age=1


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## bigT1.8t (Mar 23, 2009)

0k, i understand what you guys are talking about here. I noticed you guys are missing the hot side of the turbo charger. If you run a ko3s and make x power at x rpm and then bolt a huge compressor side on to the same ko3s hot side you will make reasonably close numbers. one of the main reasons larger turbos create bigger power is because they are able to flow more through the hot side thus decreasing restriction in the exhaust manifold and allowing for a greater volume of air to pumped through. And with this in mind you can take in a greater volume of air which is where the larger compressor comes into play. 
View it like this, take a typical pump you use to fill up an air mattress lets say. with no restriction on the inlet the volume of air will be grater and the mattress will fill up to x psi. now take your hand and cover the inlet, the mattress will fill up with the same X pressure but at a slower rate. 
So with less restriction you are able to force a greater volume of air into the engine at 15psi than you would be able to with restriction ie. ko3s. 
not only that but with a greater volume of air comes a greater volume of fuel resulting in an exponentially larger outflow. thus making greater power. 
I think someone should measure the exhaust flow with a ko3s and gt3076r at the same psi in order to find some real answers. agreed? 
Hope i didnt just make myself look like a fool lol 
im just trying to contribute.










_Modified by bigT1.8t at 9:40 PM 8-27-2009_


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## 04VDubGLI (May 20, 2005)

While there's truth to that, a comparable situation would be to take a 3076 turbine wheel + housing and strap a k03s comp wheel onto it (neglect the surge and everything). You'd find that the k03s compressor wheel would flow at it's max, but it'd still only make a bit more than it would with it's own regular turbine wheel/housing. So, instead of spiking 210whp and tapering to like 190whp at redline it'd probably make like 220whp from 4-7k rpms or something. It certainly won't suddenly up and make 30R numbers. The most effective setups are usually like a 1:1 ratio of comp to turbine wheels. Then the choke is pretty equal and the pressure ratios are easy to deal with.


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## bigT1.8t (Mar 23, 2009)

EXACTLY!!! so isnt this argument void if were neglecting to take the hot side and exhaust gas flow into consideration? 
I find this topic riveting lol


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## 04VDubGLI (May 20, 2005)

*Re: (bigT1.8t)*


_Quote, originally posted by *bigT1.8t* »_EXACTLY!!! so isnt this argument void if were neglecting to take the hot side and exhaust gas flow into consideration? 
I find this topic riveting lol

Depends on which argument you're asking about? To be honest, I also find this very interesting. It certainly has made me reconsider what I know about how an engine ingests added air (air + fuel = power in basics) and also reconsider the effects of volume relative to airflow from turbos. And it's also made me think more about simple physics/chem and how they can easily apply - take it back to the roots; these things have been around for almost a century (FI in general sort of). IIRC the 3076 has gone relatively unchanged (from Garrett) in a couple of decades. The billet wheels that companies are now experimenting with, the different trims (extended tip from bullseye), the different numbers of blades for inducers/exducers, etc... Finally starting to get some newer tech into these things!


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## thom337 (Oct 13, 2007)

*Re: FV-QR (50trim S)*


_Quote, originally posted by *50trim S* »_i would like to see a dyno of a k03 and 35r at say 12 psi to redline and im PRETTY sure the 35r will make more power even if you make in intake temps the same
if you disagree, prove it
plain and simple because im on the straw and hose theory if thats what you want to call it .

If both turbos are at 12 psi, and the same IAT, at that RPM, they will be flowing the same mass of air. So, the engine will be able to inject the same quantity of fuel for a given AFR, and will make the same power...fact. 

_Quote, originally posted by *50trim S* »_
why according to you and that other guy they both will make the same power if the IAT are the same?


If temperature and pressure are the same, at the same RPM, they will make the same power.

_Quote, originally posted by *The*Fall*Guy* »_Some guys bring up valid points.. Some guys post formulas that they googled to make themselves look smart.. When in reality the posted formula is only loosely related to the discussion at best... 

I didn't google any formulas. I just made them myself from common sense about internal combustion engine operation. Which part of the equation specifically do you have a problem with? 


_Quote, originally posted by *04VDubGLI* »_
Whenever turbo A (whatever you want to make it) flows 100 g/s across a MAF and turbo B flows 100 g/s across the same MAF then they are going to be REALLY close in power. Now you can insert assumptions about temps. What you keep misposting about is it doesn't matter what PSI turbo A is making or what PSI turbo B is making (now, ignoring pressure ratios is not correct, but let's assume both are within the same level of efficiency - call it a Bullseye S256 and 3076 if it makes you feel better). The important thing here is that they are both flowing 100 g/s (temp, blah blah blah = the same b/c of IC). Now, if turbo A needs 100psi to flow 100 g/s and turbo B uses 50psi to flow 100 g/s it's irrelevant to the amount of power being generated. 


At the intake manifold, what determines mass flow to the cylinder? PRESSURE, VOLUME FLOW (controlled by engine displacement and speed), and TEMPERATURE. If two turbos have identical pressure and temperature at the same rpm, they are by definition producing the same mass flow of air. At these conditions, the mass flow rates across the MAF should be the exact same plus or minus any small transients which are occurring. 

_Quote, originally posted by *bigT1.8t* »_EXACTLY!!! so isnt this argument void if were neglecting to take the hot side and exhaust gas flow into consideration? 
I find this topic riveting lol

Yes, the effects of the turbine are of course important. These cause pumping losses which play into the effects of the thermodynamic efficiency of the engine. The original discussion we were having was simply based on what is important about compressor performance, which is MASS FLOW, not VOLUME flow. In other words, with no other information, stating a compressors cfm is completely useless, because you have no idea what about the density of the air which is flowing at that CFM.


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## bigT1.8t (Mar 23, 2009)

agreed. 
Yea, i think this topic has really made me think about what to consider when looking to go larger than my original setup. I think this topic is really what we should be talking about on this forum


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## thom337 (Oct 13, 2007)

*Re: (NOLA_VDubber)*


_Quote, originally posted by *NOLA_VDubber* »_this thread needs more T-s diagrams


For real....anyone heard of entropy here? Thats why a K03 doesn't make the same intake temps as a GT28RS with both at 4k rpm and 20psi.


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## 04VDubGLI (May 20, 2005)

*Re: FV-QR (thom337)*


_Quote, originally posted by *thom337* »_
If both turbos are at 12 psi, and the same IAT, at that RPM, they will be flowing the same mass of air. So, the engine will be able to inject the same quantity of fuel for a given AFR, and will make the same power...fact. 
*FALSE. Seriously... how can you believe this? If a k03s is at 12psi and a 30R is at 12psi... they're not even on the same map @ 7000rpms. THAT IS A FACT!
Ok... let's take a looksi. I have a k04-02x. I hold 20psi to redline. There's a local with a 30R who runs 20psi on pump gas. I run my k04-02x on WMI + Race and we both have identical (mine are better actually) IATs. Who makes more power? Ah... Really? 30R
Now, let's revise this... my k04 and the 30R both flow 100 g/s and are both on 93oct. Who's making more power at 7000rpms? Whoever has the lower IATs - the only time your theory works! *

If temperature and pressure are the same, at the same RPM, they will make the same power.
*Again, do I need to go back to what I just explained? I can make examples all day long. Pressure is a moot point. Intake MASS, very VERY important. *
I didn't google any formulas. I just made them myself from common sense about internal combustion engine operation. Which part of the equation specifically do you have a problem with? 
*Common sense says that our engines can only ingest what the cylinders can hold... I follow that. That's why it's called FORCED INDUCTION. YOU FORCE more air into the cylinders. That's why all things constant, an engine w/FI will make MORE power than the same exact engine w/o one. It FORCES air into the engine (more than the engine would like to have really). Recall the basics here... AIR + FUEL = POWER. More air requires more fuel ---> more power. Why ever change off of stock injectors? I mean... I'm going to run my 30R at 15psi, I don't need to change them right? It doesn't stuff more air into the engine or anything silly like that?*









At the intake manifold, what determines mass flow to the cylinder? PRESSURE, VOLUME FLOW (controlled by engine displacement and speed), and TEMPERATURE. If two turbos have identical pressure and temperature at the same rpm, they are by definition producing the same mass flow of air. At these conditions, the mass flow rates across the MAF should be the exact same plus or minus any small transients which are occurring. 
*Pressure isn't mass flow. Plain and simple, 30psi on one turbo will NEVER = 30 psi on another (not even every 30R produced will be that precise). 
Ok, non auto example, take a household fan and put it in a room. It blows air around the room (creating a pressure difference). Now, take an industrial fan and put it in the same room. It blows air, but a lot more of it (you can feel this difference). They can create the same exact PRESSURE difference in the room, but the larger fan moves a larger volume (mass) of air while creating the same pressure. *

Yes, the effects of the turbine are of course important. These cause pumping losses which play into the effects of the thermodynamic efficiency of the engine. The original discussion we were having was simply based on what is important about compressor performance, which is MASS FLOW, not VOLUME flow. In other words, with no other information, stating a compressors cfm is completely useless, because you have no idea what about the density of the air which is flowing at that CFM.
*I completely agree with your statement about comp performance being mass flow. That's entirely correct. Now, just understand that PRESSURE != MASS FLOW. However, volumetric flow is much closer akin to mass flow. Again, density = mass/volume. Increase mass w/o changing volume and you get more dense. *
*Stating a compressor's CFM (basically lb/min = mass flow = you said is important) is the ONLY way to rate the compressor. It's a standard measure to calculate the amount of air the compressor can move, regardless of pressure. Now, once you know what engine you're using it on you can calculate the pressure necessary to get the maximum flow from a compressor. That's why there's comp maps. You can calculate how it will work on ANY engine, not just 1.8t/2.0t/whatever. *


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## 20aeman (Jun 8, 2006)

*Re: FV-QR (04VDubGLI)*

IAT is perhaps the wrong word to use. 
Which balloon will be bigger:
Let's say you fill a balloon with air to X size with 200 degree oxygen, you then subsequently throw the balloon in a fridge that cools the air to 50 degrees. (k04 with water/meth)
You then fill a balloon with air to X size with 50 degree oxygen, but you keep it at 50 degrees. (35R)
Assuming X is a constant, you can see why a 35r will make more power...it does flow more, but it's a function of temperature.
Also, in this analogy, the turbo is the knot in the balloon holding the pressure within.

--------------------------------------------------------------------------------------------
ideal gas law:
PV=nRT
let's get rid of nR, because we aren't concerned with exact numbers...so in general, 
P=T*stuff
-----------
V
Since the volume will be the same, and "stuff" doesn't matter here, we can deduce that 
P=T (not saying pressure equals temperature...just showing that there is a relationship)
The higher the temperature, the higher the pressure will be for any given amount of air. So your boosting 20psi on a k04, but you could cram more air molecules in with the 35r for that given boost pressure. This is of course due to temperature.....which in turn is due to efficiency at the compressor.

So IATs isn't the exact term I would use....efficiency at the compressor maybe?
If you compare a ko4 at a given compressor efficiency to a 35R at the same given compressor efficiency at boost pressure that permits that to happen at a given RPM...then they will make comparable power .........god knows if this scenario is even possible. 







/thread 

_Modified by 20aeman at 4:21 AM 8-28-2009_


_Modified by 20aeman at 4:27 AM 8-28-2009_


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## 50trim S (Jun 3, 2008)

*Re: FV-QR (thom337)*


_Quote, originally posted by *thom337* »_
If temperature and pressure are the same, at the same RPM, they will make the same power


i will not believe this at all until i see it so prove it 
i just don't see how this can be true at all
anyone else agree with me?
just because the psi's are the same doesn't mean that the volume of air being flowed are equal
for example blow 15 psi through a 1 inch tube and then blow 15 psi through a 3 inch tube and the volume of air produced through both tubes are not going to be equal. To me its that simple
thats why a inch exhaust is a restriction and a 3 inch exhaust isn't


_Modified by 50trim S at 4:25 AM 8-28-2009_


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## 20aeman (Jun 8, 2006)

*Re: FV-QR (50trim S)*


_Quote, originally posted by *50trim S* »_
i will not believe this at all until i see it so prove it 
i just don't see how this can be true at all
anyone else agree with me?

no


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## 50trim S (Jun 3, 2008)

*Re: FV-QR (20aeman)*


_Quote, originally posted by *20aeman* »_
no

so you think 10psi from a 42 r will produce the same amount of air as a k03?
that doesn't make sense at all


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## 20aeman (Jun 8, 2006)

*Re: FV-QR (50trim S)*


_Quote, originally posted by *50trim S* »_
so you think 10psi from a 42 r will produce the same amount of air as a k03?
that doesn't make sense at all

Like I said, it's not a function of boost pressure, but one of compressor efficiency. the greater the disparity between turbos, the less the likelyhood.


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## 20aeman (Jun 8, 2006)

*Re: FV-QR (50trim S)*


_Quote, originally posted by *50trim S* »_
for example blow 15 psi through a 1 inch tube and then blow 15 psi through a 3 inch tube and the volume of air produced through both tubes are not going to be equal. To me its that simple
thats why a inch exhaust is a restriction and a 3 inch exhaust isn't

_Modified by 50trim S at 4:25 AM 8-28-2009_

right...but the charge pipe/combustion chamber volume is fixed.
But I've come to the understanding that I'm arguing semantics. So I'm gonna stop.


_Modified by 20aeman at 5:05 AM 8-28-2009_


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## enginerd (Dec 15, 2001)

*Re: (BoostinBejan)*

I find it humorous that the first post in this thread has incorrect information, and several people on here are agreeing with it. Big turbos make more power at the same boost, RPM and the same intake temperature and the reason is the exhaust side. 
Tiny turbos can have 40+ psi of backpressure in the exhaust manifold. That means that when the engine is at TDC and has finished the exhaust cycle there is 40+ psi of exhaust trapped in the cylinder. 
You can't have a high volumetric efficiency if you cant get the exhaust out of the cylinder. You can't run lot's of ignition timing if there is 1800 degree air trapped in the cylinder and heating the fresh cool air coming in. 
Big turbos lower the exhaust backpressure. That's why you can make big power at lower boost levels with a larger turbo there is a much lower exhaust backpressure. 
If you want to learn about turbo's/compressors -then do so in a library not on the internet. Amazon is good and has lots of good books on the subject. 
Corkey Bell - Maximum boost is good but a bit old and opinionated
A Graham Bell - "Forced induction performance tuning" Is another good one


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## thom337 (Oct 13, 2007)

*Re: (enginerd)*


_Quote, originally posted by *enginerd* »_
I find it humorous that the first post in this thread has incorrect information, and several people on here are agreeing with it. Big turbos make more power at the same boost, RPM and the same intake temperature and the reason is the exhaust side. 


The original context of the thread was talking about compressors only. If you have the same charge density at the same RPM, the engine will produce the same power. If you have a smaller (more restrictive) turbine, the exhaust stroke will eventually absorb more work from the cycle than a large turbine would, this is part of the pumping losses of the engine represented in the Efficiency term in the power equation I posted earlier. 
The entire point of the thread was not to say big turbos don't make power, we all know that they do. The point is to say that people keep on quoting turbos in cfm and then making a horsepower correleation to that which is vague at best, as well as referring to bigger turbos as "pushing more air volume through the engine" which is incorrect.


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## thom337 (Oct 13, 2007)

*Re: (enginerd)*


_Quote, originally posted by *enginerd* »_
I find it humorous that the first post in this thread has incorrect information, and several people on here are agreeing with it. 


Which parts exactly? Again, this conversation was transplanted from another thread in which the scope of conversation was flow from the compressor.


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## thom337 (Oct 13, 2007)

*Re: FV-QR (20aeman)*


_Quote, originally posted by *20aeman* »_IAT is perhaps the wrong word to use. 
So IATs isn't the exact term I would use....efficiency at the compressor maybe?


IAT results from what? The exit temperature of the compressor which comes from the efficiency, minus whatever cooling you can get from expansion, intercoolers, chemical means. IAT was being used as a reference to the temperature of air in the manifold, I don't see how that is a bad word to use...it is the intake air tempoerature and is extremely important to the density of the air charge entering the cylinders.


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## thom337 (Oct 13, 2007)

*Re: FV-QR (50trim S)*


_Quote, originally posted by *50trim S* »_
so you think 10psi from a 42 r will produce the same amount of air as a k03?
that doesn't make sense at all


No one said that. What was said that a 42r and K03 both at the same boost pressure, at the same rpm, with the same manifold temperature will produce the same mass flow of air. They will and they do.


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## thom337 (Oct 13, 2007)

*Re: FV-QR (04VDubGLI)*


_Quote, originally posted by *04VDubGLI* »_
FALSE. Seriously... how can you believe this? If a k03s is at 12psi and a 30R is at 12psi... they're not even on the same map @ 7000rpms. THAT IS A FACT!
*Thats why I said rpm, pressure, AND temperature must be held constant. Did you miss that part of the discussion? Obviously if the k03 is not capable of creating the same boost pressure at 7,000rpms due to inlet choking or shaft overspeed, then those three things cannot be held constant* 
Ok... let's take a looksi. I have a k04-02x. I hold 20psi to redline. There's a local with a 30R who runs 20psi on pump gas. I run my k04-02x on WMI + Race and we both have identical (mine are better actually) IATs. Who makes more power? Ah... Really? 30R
Now, let's revise this... my k04 and the 30R both flow 100 g/s and are both on 93oct. Who's making more power at 7000rpms? Whoever has the lower IATs - the only time your theory works!

*If you have identical pressure, and IATs, at the same RPM, your engines will produce the same power (of course you can change a million small variables like ignition timing, but this is assuming you both have the some process going on in cylinder). His will put more to the wheels because his engine is having less energy absorbed on the exhaust stroke due to his larger turbine. * 

If temperature and pressure are the same, at the same RPM, they will make the same power.
Again, do I need to go back to what I just explained? I can make examples all day long. Pressure is a moot point. Intake MASS, very VERY important.
*Thats what I've been saying this entire time. Mass is important. But where do we get mass flow? We can only fill the entire cylinder, so how do we get more mass in there? We A)raise the pressure b) lower the temperature. These things = increase charge density*
I didn't google any formulas. I just made them myself from common sense about internal combustion engine operation. Which part of the equation specifically do you have a problem with?
Common sense says that our engines can only ingest what the cylinders can hold... I follow that. That's why it's called FORCED INDUCTION. YOU FORCE more air into the cylinders. That's why all things constant, an engine w/FI will make MORE power than the same exact engine w/o one. It FORCES air into the engine (more than the engine would like to have really). Recall the basics here... AIR + FUEL = POWER. More air requires more fuel ---> more power. Why ever change off of stock injectors? I mean... I'm going to run my 30R at 15psi, I don't need to change them right? It doesn't stuff more air into the engine or anything silly like that?

*Where are you gathering from anything that I said that larger turbos don't flow more mass air? I have never said that they don't deliver more mass air. * 

Pressure isn't mass flow. Plain and simple, 30psi on one turbo will NEVER = 30 psi on another (not even every 30R produced will be that precise).
*Did I say pressure was mass flow? Haha, where are you pulling this stuff from? What I said was that pressure and temperature are DIRECTLY proportional to mass flow. Mass flow is a VOLUME flow with A DENSITY. DENSITY is controller by temperature and pressure.* 
Ok, non auto example, take a household fan and put it in a room. It blows air around the room (creating a pressure difference). Now, take an industrial fan and put it in the same room. It blows air, but a lot more of it (you can feel this difference). They can create the same exact PRESSURE difference in the room, but the larger fan moves a larger volume (mass) of air while creating the same pressure.

*Completely different situation* 

I completely agree with your statement about comp performance being mass flow. That's entirely correct. Now, just understand that PRESSURE != MASS FLOW. However, volumetric flow is much closer akin to mass flow. Again, density = mass/volume. Increase mass w/o changing volume and you get more dense.

* Again...please point to anywhere where I said that pressure = mass flow. Volumetric flow is nothing like mass flow. You can have two completely equal volumetric flows and they can have EXTREMELY different mass flows. This is the point I've been trying to convey this entire thread.* 
Stating a compressor's CFM (basically lb/min = mass flow = you said is important) is the ONLY way to rate the compressor. It's a standard measure to calculate the amount of air the compressor can move, regardless of pressure. Now, once you know what engine you're using it on you can calculate the pressure necessary to get the maximum flow from a compressor. That's why there's comp maps. You can calculate how it will work on ANY engine, not just 1.8t/2.0t/whatever. 
*CFM is not bassically lb/min. CFM is not a good way to rate a compressor. Lb/min is a good way to rate a compressor. CFM with more details is also a good way to rate a compressor, because with pressure and efficiency data you can figure out MASS FLOW. A compressor map with volume labels is so that you can plug in your volumetric flowrate at a certain RPM and figure out what pressure you need to get a certain MASS flow rate which determines you power output.*


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## 04VDubGLI (May 20, 2005)

1 ft^3 air = 0.0807 lbs
Therefore, cubic feet per minute can easily be lb/min. 
That's about all I can contribute. I've tried to think of a different example, but it seems at least we're somewhat agreeing on air mass.


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## thom337 (Oct 13, 2007)

*Re: (04VDubGLI)*


_Quote, originally posted by *04VDubGLI* »_1 ft^3 air = 0.0807 lbs
Therefore, cubic feet per minute can easily be lb/min. 
That's about all I can contribute. I've tried to think of a different example, but it seems at least we're somewhat agreeing on air mass.

1 ft^3 is only .0807 lbs at one precise point. That tells nothing about the performance of a compressor. And that point is a specific pressure and temperature. When you rate a compressor in cfm, you are only telling part of the story because as we agree, in the end the important thing is MASS flow and how many molecules of air you can get to react with molecules of fuel.


_Modified by thom337 at 11:42 AM 8-28-2009_


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## [email protected] (Oct 23, 2008)

*Re: (thom337)*

Well, we cannot overfill the cylinders although the bigger compressors try. You cant ignore the engine side in relation to efficiency and time. The smaller compressor would work much harder to maintain pressure and efficiency at a specific rpm. For example:
K03 at a low rpm where VE's are lower will have an easier time maintaining psi. Thus, not needing work as hard. At higher rpm's it'll need to work harder
GT28R wheel can maintain this easier at a higher rpm when the engine consumes/expels more. Thus needing to flow more..
There will be a brief overlap period b/w the two wheels, but if you are looking at psi maintained and rpm's there will be a big disparity b/w the two, both high and low. The smaller wheel will actually produce more flow down low, especially before the larger wheel has enough inertia/load to produce a positive charge. And this has very little to do w/ backpressure disparities..


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## thom337 (Oct 13, 2007)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_Well, we cannot overfill the cylinders although the bigger compressors try. You cant ignore the engine side in relation to efficiency and time. The smaller compressor would work much harder to maintain pressure and efficiency at a specific rpm. For example:
K03 at a low rpm where VE's are lower will have an easier time maintaining psi. Thus, not needing work as hard. At higher rpm's it'll need to work harder
GT28R wheel can maintain this easier at a higher rpm when the engine consumes/expels more. Thus needing to flow more..
There will be a brief overlap period b/w the two wheels, but if you are looking at psi maintained and rpm's there will be a big disparity b/w the two, both high and low. The smaller wheel will actually produce more flow down low, especially before the larger wheel has enough inertia/load to produce a positive charge. And this has very little to do w/ backpressure disparities..


Again, no one is saying big turbos don't make big power. Simply saying that what is important to performance is mass flow, which comes from charge density, which is directly proportional to temperature and pressure. Just think its weird that we still have people saying X cfm = Y Horsepower...CFM by itself is meaningless. 
And at the points where both turbos are making the same pressure at the same rpm, with equal IATs, they will be flowing the same mass flow. ie if you cool the K03's charge down so that it is equal to the GT28R @ 5,000 rpm and 10psi, they will be flowing the same mass air into the cylinders.


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## [email protected] (Oct 23, 2008)

*Re: (thom337)*

I find it odd that ppl argue about a small portion of what is taking place in the entire system and throughout the rpm band.. we do not care about the small overlap period..


_Modified by [email protected] at 9:22 AM 8-28-2009_


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## thom337 (Oct 13, 2007)

*Re: ([email protected])*


_Quote, originally posted by *AL[email protected]* »_I find it odd that ppl argue about a small portion of what is taking place in the entire system and throughout the rpm band.. we do not care about the small overlap period..

_Modified by [email protected] at 9:22 AM 8-28-2009_


The point is not to argue about the overlap period. The point is to realize what is important is charge density, not a meaningless CFM rating or the numbers stamped on your compressor.


_Modified by thom337 at 12:27 PM 8-28-2009_


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## [email protected] (Oct 23, 2008)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_

The point is not to argue about the overlap period. The point is to realize what is important is charge density, not a meaningless CFM rating or the numbers stamped on your compressor.

_Modified by thom337 at 12:27 PM 8-28-2009_

Well, if you want to compare apples to apples, yes. If you want to look at the more realistic picture where both turbos are reacting to the forces that make them work, then you cant adhere to such a finite way of thinking. There's are reason why maps are calculated in cfm or lbs. Its all plotted in time, pressure and VE's/percentages...


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## thom337 (Oct 13, 2007)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
Well, if you want to compare apples to apples, yes. If you want to look at the more realistic picture where both turbos are reacting to the forces that make them work, then you cant adhere to such a finite way of thinking. There's are reason why maps are calculated in cfm or lbs. Its all plotted in time, pressure and VE's/percentages...

I completely agree, but you can't just look at the cfm and and make a blanket statement about performance.


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## NOLA_VDubber (May 24, 2007)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_I find it odd that ppl argue about a small portion of what is taking place in the entire system and throughout the rpm band.. we do not care about the small overlap period..

_Modified by [email protected] at 9:22 AM 8-28-2009_

I don't think thom337 is trying to argue about turbocharger choice. He is simply stating facts about a compressor connected to an engine. For his argument, and the discussion he's trying to have, one not even need to worry about where the power comes from to drive the compressor.
He's simply stating that the vloumetric flow rate in the engine is dictated by displacement, not turbocharger compressor size. He's also stating simply that, according to the ideal gas law, two compressors generating two seperate mass flows will be equal if volumetric flow, pressure, and temperature are the same.
Its been covered that turbine choice will dictate overall power output due to pumping efficiencies of the engine, but he's not arguing this fact. I think his goal was simply to correct people's ideas about what's going on between the compressor and the engine.


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## [email protected] (Oct 23, 2008)

*Re: (NOLA_VDubber)*


_Quote, originally posted by *NOLA_VDubber* »_
I don't think thom337 is trying to argue about turbocharger choice. He is simply stating facts about a compressor connected to an engine. For his argument, and the discussion he's trying to have, one not even need to worry about where the power comes from to drive the compressor.
He's simply stating that the vloumetric flow rate in the engine is dictated by displacement, not turbocharger compressor size. He's also stating simply that, according to the ideal gas law, two compressors generating two seperate mass flows will be equal if volumetric flow, pressure, and temperature are the same.
Its been covered that turbine choice will dictate overall power output due to pumping efficiencies of the engine, but he's not arguing this fact. I think his goal was simply to correct people's ideas about what's going on between the compressor and the engine.


This I understand. If you have an engine at a given rpm, temp or whatever it will allow a finite amount of volume to run through it. That is established. But we are also talking about psi which can be achieved at all different levels of rpm. At a certain rpm, the smaller wheel will be out of its efficiency range to keep up w/ the consumption of the engine. It cannot maintain the arbitrary 15psi which the larger wheel can... Thus concludes the fact that at that juncture, the larger wheel WILL be flowing more. That is my point. I'm looking at the entire picture, not just a narrow scope...
I know that this is a conversation taking place but I have battled boosting issues all over the map for well over a decade, almost 2 on so many separate vehicles, i cant count... I have a very acute understanding of how this all works theory and applied..


_Modified by [email protected] at 12:15 PM 8-28-2009_


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## thom337 (Oct 13, 2007)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
This I understand. If you have an engine at a given rpm, temp or whatever it will allow a finite amount of volume to run through it. 

This is what I was trying to say, people were saying that bigger turbos increase the volumetric flowrate into the cylinders, which isn't true. I was simply trying to correct this idea by introducing the idea of charge density which is how it is actually working.


_Quote, originally posted by *[email protected]* »_
At a certain rpm, the smaller wheel will be out of its efficiency range to keep up w/ the consumption of the engine. It cannot maintain the arbitrary 15psi which the larger wheel can... Thus concludes the fact that at that juncture, the larger wheel WILL be flowing more. That is my point. I'm looking at the entire picture, not just a narrow scope...


Absolutely, I wasn't trying to ever say that larger wheels cant move more mass air than smaller wheels. I'm simply trying to say that they make more power because they can flow the same volume of air at a higher pressure and lower temperature, increasing charge density. 
However, if you can increase shaft speed high enough on a small turbo, even if it is very inefficient in its operation, and sufficiently cool the air such that the pressure and temperature of the air being delivered to the engine are the same as a larger compressor, they will have equal mass flow rates, and apart from pumping losses in the turbine will make the same power. I was just using this as an example of why charge density is important, not recommending people go weld their wastegates shut and try to rig up elaborate cooling setups for their post compressor air. I think we are on the same page here.


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## Vegeta Gti (Feb 13, 2003)

*Re: ([email protected])*

my car is faster than yours in a vacuum. SO HA!!


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## [email protected] (Oct 23, 2008)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
However, if you can increase shaft speed high enough on a small turbo, even if it is very inefficient in its operation, and sufficiently cool the air such that the pressure and temperature of the air being delivered to the engine are the same as a larger compressor, they will have equal mass flow rates, and apart from pumping losses in the turbine will make the same power. I was just using this as an example of why charge density is important, not recommending people go weld their wastegates shut and try to rig up elaborate cooling setups for their post compressor air. I think we are on the same page here.


This is what I'm talking about. The above scenario just doesnt happen. You'll just end up w/ a cooked bearing and so much backpressure that the small shaft will surely pull loose from the turbine wheel. If its just the compressor, the amount of drag or air friction that it will experience will surely slow it down and superheat the air while wanting to bend the fins the other way... These hypotheticals cant even be duplicated in a lab as its beyond physical limitations. I'm talking K03 vs GT40 that you've previously illustrated...


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## thom337 (Oct 13, 2007)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
This is what I'm talking about. The above scenario just doesnt happen. You'll just end up w/ a cooked bearing and so much backpressure that the small shaft will surely pull loose from the turbine wheel. If its just the compressor, the amount of drag or air friction that it will experience will surely slow it down and superheat the air while wanting to bend the fins the other way... These hypotheticals cant even be duplicated in a lab as its beyond physical limitations. I'm talking K03 vs GT40 that you've previously illustrated...


Like I said, I'm not saying for people to do this. I never said that running a K03 to ridiculous shaft speeds was a good idea. You are missing the entire point of what I said. Most of my examples however were say a K03 at 5k rpm @ 5psi vs a GT40 at 5k rpm @ 5psi both with the same IATs, which is not that absurd. And yes, at these conditions they will be producing the same mass flow. I'm not saying that the K03 can make more power than a GT40. I'm just saying that people need to realize what is actually making the power is mass air which comes from volumetric flow with a specific density, not some cfm number they pull off of a backasswards website they found through google.
I'm just illustrating the importance of charge density. The entire point of this thread was that volume flow is not something you dictate to the turbo and go from there, it is controlled by the engine. The turbo creates pressure at a temperature (controlled by efficiency) which occur at a specific volumetric flowrate. The turbo is there to increase charge density, which allows more mass to enter the fixed volume of the cylinders.


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## 20aeman (Jun 8, 2006)

*Re: FV-QR (thom337)*


_Quote, originally posted by *thom337* »_
IAT results from what? The exit temperature of the compressor which comes from the efficiency, minus whatever cooling you can get from expansion, intercoolers, chemical means. IAT was being used as a reference to the temperature of air in the manifold, I don't see how that is a bad word to use...it is the intake air tempoerature and is extremely important to the density of the air charge entering the cylinders.

Right...but where is IAT measured? If you really wanted to see which turbo was going to "flow" more due to cooler charge temps, the iat sensor would be attached immediately after the compressor housing..or maybe in the compressor housing.
If you measure it at the manifold, where IAT is traditionally measured, water/meth, intercoolers, etc on a smaller turbo will make the IATs similar to a larger turbo...but there will still be a large disparity in power (see my balloon diagram thingy). IATs for this argument should be measured before any cooling measures, that way, two different sized turbos can be compared.


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## thom337 (Oct 13, 2007)

*Re: FV-QR (20aeman)*


_Quote, originally posted by *20aeman* »_
Right...but where is IAT measured? If you really wanted to see which turbo was going to "flow" more due to cooler charge temps, the iat sensor would be attached immediately after the compressor housing..or maybe in the compressor housing.
If you measure it at the manifold, where IAT is traditionally measured, water/meth, intercoolers, etc on a smaller turbo will make the IATs similar to a larger turbo...but there will still be a large disparity in power (see my balloon diagram thingy). IATs for this argument should be measured before any cooling measures, that way, two different sized turbos can be compared.

If you're cooling post compressor outlet , the pressure will drop, and the signal to the wastegate will decrease, so the shaft speed will increase until the same pre-set pressure is acheieved. Intercooling / water injection obviously isn't changing the compressor itself, its making efficiency changes after the fact. However, in the end its the conditions in the intake manifold that matter. So, again if you can achieve the same pressure and temperature at the same rpm in the manifold you will generate the same mass flow.


_Modified by thom337 at 10:00 PM 8-28-2009_


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## Bryan on Boost (Aug 8, 2009)

*Re: (enginerd)*


_Quote, originally posted by *enginerd* »_
I find it humorous that the first post in this thread has incorrect information, and several people on here are agreeing with it. Big turbos make more power at the same boost, RPM and the same intake temperature and the reason is the exhaust side. 
Big turbos lower the exhaust backpressure. That's why you can make big power at lower boost levels with a larger turbo there is a much lower exhaust backpressure. 

Yes, I commented way earlier about how this needs to be taken into consideration. This entire discussion is moot unless you take into consideration all variables involved. You CANNOT only talk about the compressor side. Oh and the topic says "turbo theory", not compressor wheel theory ignoring all other factors. And again, lets keep it friendly guys!


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## bigT1.8t (Mar 23, 2009)

i agree, I think there us much more to consider with talking turbos. My friend runs a 3071r on his tt and i am running k04 001. We recently took a VAG cruise to flagstaff (elevation 7000ft). as my boost pressure reached 19psi i experienced a boost cut out! My turbine shaft reached a speed at which it could not perform it's function properly. my smug friend in his tt kept the same psi and was able to make the same power because of the larger housings both exhaust and intake. The turbo was able to spin a higher rpm thus accounting for the thiner air. Even though our iats were relatively the same our mass air flow greatly differed. Simply because the turbos were more efficient. 
So doesn't this prove the ait reliance theory incorrect?


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## The*Fall*Guy (Aug 10, 2009)

*Re: (bigT1.8t)*

In my mind it does.. All factors considered. Although I'm sure someone is reaching for his slide rule and calculator to attempt to prove the contrary..


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## bigT1.8t (Mar 23, 2009)

hahaha watch, its gonna get holes shot through it lol


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## The*Fall*Guy (Aug 10, 2009)

*Re: (bigT1.8t)*

Careful bro... Those sliderules can be deadly weapons... In fact I think I hear a bench grinder humming away right now.. Some nerd is sharpening his slide rule up as we speek.. Watch your back.. He had a spooky look on his face as he pushed his glasses up onto his nose, and slid that pocket-protector into his button down shirt as if he was preparing for battle..


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## killa (Nov 26, 2000)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_Do bigger turbos flow more volume of air through the engine? No.
Volumetric flow in an engine is controlled by engine displacement and RPM. The gains from a larger turbocharger come from its ability to flow air more efficiently. 
So, at the same RPM on the same engine, a k03 sport and GT-4088 are flowing the same VOLUME of air out of the compressor. 
Are they flowing the same mass of air? NO. 
Does volume flow have anything to do with performance by itself? NO!
Performance comes from mass flow of air, because it gives you the ability to burn more mass fuel and release more heat energy, which creates pressure, which creates force, which when acting over a distance creates torque, which at a speed creates power, etc etc etc.
Reading compressor maps for volume using pressure is not how its supposed to work. You are supposed to get your volume from the VOLUME FLOW of the engine, then you can use your boost pressure at that volume flow, combined with the compressor efficiency to calculate MASS flow.
_Modified by thom337 at 3:45 PM 8-27-2009_

_Modified by thom337 at 3:48 PM 8-27-2009_

Don't bother, they seem to think that you can fit more air into the same volume at the same psi...


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## bigT1.8t (Mar 23, 2009)

haha.


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## JGarcia9102 (Feb 1, 2009)

*Re: (bigT1.8t)*

i have a 1 litre jar full of air compressed at 100 psi. how many litres of air do i have?


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## killa (Nov 26, 2000)

*Re: (JGarcia9102)*


_Quote, originally posted by *20aeman* »_
Like I said, it's not a function of boost pressure, but one of compressor efficiency. the greater the disparity between turbos, the less the likelyhood.

Also, a larger compressor will need a larger turbine to be efficient, this will bring your VE up since a larger turbine wheel will get rid of more backpressure.
The larger compressor will achieve the same pressure at a lower shaft speed (rpm), less rpm = less heat = lower intake temps http://****************.com/smile/emthup.gif


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## killa (Nov 26, 2000)

I had this argument with Tony1 before:
NO NO NO NO NO!!! lol, Forget about CFM. If there is 10psi in the manifold on said engine, then it's 10psi, period. The only way you can change the amount of air that will enter the engine is to change the density. The only way to do that is to change the temperature. If the charge temperature is 80 deg., then it's doesn't matter how big the turbo is, the same amount of air is going in the motor. The engine is the restriction, and the restriction is what makes "boost". A smaller turbo will eventually not be able to keep up with the airflow requirements, and boost will drop. The amount of air the turbo can flow is irrelevant if boost is constant. If it's is flowing enough to maintain the same boost as a big turbo, then temperature is the only variable that can change the MASS of air entering the engine. Volume is fixed. So, on the compressor side you have temperature, which is efficiency (which is why we have compressor maps), and on the exhaust side you have exhaust backpressure. 95% of the time, the larger turbo is going to have a larger exhaust wheel/housing and that's where most of the power comes from. And to answer the original question, yes, a bigger turbo greatly raises the knock limit on a motor, because of both lower intake temps and less exhaust backpressure. The whole CFM/volume thing is a VERY common misunderstanding.
------------------------

I'm done arguing


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## The*Fall*Guy (Aug 10, 2009)

*Re: (killa)*


_Quote, originally posted by *killa* »_I had this argument with Tony1 before:
NO NO NO NO NO!!! lol, Forget about CFM. If there is 10psi in the manifold on said engine, then it's 10psi, period. The only way you can change the amount of air that will enter the engine is to change the density. The only way to do that is to change the temperature. If the charge temperature is 80 deg., then it's doesn't matter how big the turbo is, the same amount of air is going in the motor. The engine is the restriction, and the restriction is what makes "boost". A smaller turbo will eventually not be able to keep up with the airflow requirements, and boost will drop. The amount of air the turbo can flow is irrelevant if boost is constant. If it's is flowing enough to maintain the same boost as a big turbo, then temperature is the only variable that can change the MASS of air entering the engine. Volume is fixed. So, on the compressor side you have temperature, which is efficiency (which is why we have compressor maps), and on the exhaust side you have exhaust backpressure. 95% of the time, the larger turbo is going to have a larger exhaust wheel/housing and that's where most of the power comes from. And to answer the original question, yes, a bigger turbo greatly raises the knock limit on a motor, because of both lower intake temps and less exhaust backpressure. The whole CFM/volume thing is a VERY common misunderstanding.
------------------------

I'm done arguing
Now you see this guys? This is how its done.. This guy just gutted me with his sliderule.. Well done


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## Agtronic (May 14, 2001)

killa, thank you!!!!!!!!!!


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## [email protected] (Oct 23, 2008)

*Re: (killa)*


_Quote, originally posted by *killa* »_The whole CFM/volume thing is a VERY common misunderstanding.
------------------------

I'm done arguing


Again, let me repeat myself, until one runs out of compressor efficiency (CFM starts taking over in a hurry), when the engine can consume more. You cant ignore one aspect while paying attention to another... but i understand the point, just not the application...


_Modified by [email protected] at 6:14 PM 8-28-2009_


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## 04VDubGLI (May 20, 2005)

*Re: (killa)*


_Quote, originally posted by *killa* »_ If it's is flowing enough to maintain the same boost as a big turbo, then temperature is the only variable that can change the MASS of air entering the engine. Volume is fixed. So, on the compressor side you have temperature, which is efficiency (which is why we have compressor maps), and on the exhaust side you have exhaust backpressure. 95% of the time, the larger turbo is going to have a larger exhaust wheel/housing and that's where most of the power comes from. The whole CFM/volume thing is a VERY common misunderstanding.


So, a MAF sensor is before the turbo. It doesn't care how hot the turbo makes the air. You're telling me you can prove a 30R running 15psi @ 7000rpms and my k04-02x running 15psi @ 7000rpms move the same amount of air past the MAF sensor? Unless you're saying something else is measuring mass? It's fair to assume here that the ambient air temp is identical.
And, just as a second question (a bit of rhetoric though), if I take my k04 compressor wheel and put it on a 3076 back housing I'll make as much power as a 30R? 

_Quote, originally posted by *killa* »_95% of the time, the larger turbo is going to have a larger exhaust wheel/housing and that's where most of the power comes from.

I still can't possibly reason how anyone can think CFM (read lb/min equiv) is not relevant? They sell fans (turbines) in CFM ratings, they sell air compressors in CFM ratings (which oddly, all air compressors use PSI to work, but they're not created equally? sounds kind of similar?), same with those little hand held air blowers... oh, a really good example, how about a CARB? No one here knows carbs, but they're magical little fuel distribution centers that used to sit on intake manifolds. I guess a 350 CFM carb is the same as an 800 CFM carb. Just like a 350 CFM compressor wheel is just like an 800 CFM compressor wheel. The only difference is the 350 CFM one has a pesky little turbine wheel holding it back (cause they totally take that into consideration when making the ratings







)
Now, just so it's clear, I'm not at all negating the "true" effects this has on an engine, but until the conceptual portion is understood no reason to go on arguing much more difficult things (why is it a big port head is better (most apps) than a small port head? lots of variables here...)


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## bigT1.8t (Mar 23, 2009)

im just done with this thread...


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## Agtronic (May 14, 2001)

_Quote, originally posted by *04VDubGLI* »_And, just as a second question (a bit of rhetoric though), if I take my k04 compressor wheel and put it on a 3076 back housing I'll make as much power as a 30R?

At 2000 RPM, set at ~7 psi, the K04 compressor would probably make MORE power than the 30R.
At 6000 RPM, set at 25 psi, the 30R would make a lot more power. 
This is why there are flow maps, and cfm ratings. The compressors have peak efficiencies that are relative to pressure and flow. 

_Quote, originally posted by *04VDubGLI* »_I still can't possibly reason how anyone can think CFM (read lb/min equiv) is not relevant? They sell fans (turbines) in CFM ratings, they sell air compressors in CFM ratings (which oddly, all air compressors use PSI to work, but they're not created equally? sounds kind of similar?), same with those little hand held air blowers... oh, a really good example, how about a CARB? No one here knows carbs, but they're magical little fuel distribution centers that used to sit on intake manifolds. I guess a 350 CFM carb is the same as an 800 CFM carb. Just like a 350 CFM compressor wheel is just like an 800 CFM compressor wheel. The only difference is the 350 CFM one has a pesky little turbine wheel holding it back (cause they totally take that into consideration when making the ratings







)

Now, you're just confusing different theories and making things more confusing. Putting on an 800 cfm carb on an engine that was equipped with an 350 cfm one does not make the motor flow 800 cfm. It's the same as putting in 630 cc injectors on a motor and running it at 3 psi. (but never mind that ...)
A compressor that is rated to 600 cfm means that it is efficient to that amount of flow, _if the engine it is mounted to were to inhale that much air_. It does NOT mean that it WILL flow that much air at less boost than the smaller one.
OF COURSE CFM ratings are important, they tell you how that compressor will behave on a given motor. What killa is saying is that the CFM rating of the compressor does not dictate how much CFM the engine will flow.[/quote]

_Quote, originally posted by *04VDubGLI* »_Now, just so it's clear, I'm not at all negating the "true" effects this has on an engine, but until the conceptual portion is understood no reason to go on arguing much more difficult things (why is it a big port head is better (most apps) than a small port head? lots of variables here...)

The larger port head reduces the restriction, allowing the engine to flow more CFM on its own. Don't forget, the only way to increase FLOW, is to increase PRESSURE, or reduce RESTRICTION.


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## animaniac (May 26, 2005)

*Re: (JGarcia9102)*


_Quote, originally posted by *JGarcia9102* »_i have a 1 litre jar full of air compressed at 100 psi. how many litres of air do i have?

6.8 litres if it was at 14.7 psi before compression, but technicaly it all depends on what pressure the air was before compression!


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## thom337 (Oct 13, 2007)

*Re: (04VDubGLI)*


_Quote, originally posted by *04VDubGLI* »_
So, a MAF sensor is before the turbo. It doesn't care how hot the turbo makes the air. You're telling me you can prove a 30R running 15psi @ 7000rpms and my k04-02x running 15psi @ 7000rpms move the same amount of air past the MAF sensor? Unless you're saying something else is measuring mass? It's fair to assume here that the ambient air temp is identical.


We're talking about the same intake air temps as well. Think about it. If you are cooling the air after a k04-02x, the air takes up less volume. Therefore, to maintain your pressure setting, the turbo will speed up because exhaust is not being diverted around the turbine...now, at some point the turbine or inlet of the k04-02x will choke or it will get to a shaft speed which is to dangerous so it may not even be able to make 15 psi at 7,000 rpms. Before the point where the turbine effects start to slow the compressor, the turbos will flow the same mass flow of air as long as the temperature, pressure, and rpm are the same....its still as true as it was when this thread began.

_Quote, originally posted by *04VDubGLI* »_
And, just as a second question (a bit of rhetoric though), if I take my k04 compressor wheel and put it on a 3076 back housing I'll make as much power as a 30R? 




You still are ignoring the hundred times I have said that the turbine effects the pumping losses of the engine....yes bigger turbos can make more power at the same mass flow rates because they generate less pressure on the piston face during the exhaust stroke. But two compressors at the same rpm, temperature, and pressure are still making the same mass flow, there is no getting around it.

_Quote, originally posted by *04VDubGLI* »_
I still can't possibly reason how anyone can think CFM (read lb/min equiv) is not relevant? They sell fans (turbines) in CFM ratings, they sell air compressors in CFM ratings (which oddly, all air compressors use PSI to work, but they're not created equally? sounds kind of similar?), same with those little hand held air blowers... oh, a really good example, how about a CARB? No one here knows carbs, but they're magical little fuel distribution centers that used to sit on intake manifolds. I guess a 350 CFM carb is the same as an 800 CFM carb. Just like a 350 CFM compressor wheel is just like an 800 CFM compressor wheel. The only difference is the 350 CFM one has a pesky little turbine wheel holding it back (cause they totally take that into consideration when making the ratings







)


 
ahahaha.







When was the last time you read an air compressor rating? They are rated at say 6 cfm AT 90psi or 3 cfm AT 60 psi. Thats because volume flow by itself means very little. In terms of a IC engine, volume flow by itself MEANS NOTHING. And anyways, say someone DID rate an air compressor at just a cfm, that doesn't make you right, that just makes them WRONG. Argue with facts, not with other mistakes people have made. Two wrongs don't make a right.
As for fans, fans are not pressure generating devices. They flow against atmospheric pressure, and aren't meant to build static pressure. Sometimes they do, due to stagnation of dynamic pressure caused by the velocity of air they produce, but its generally pretty small. Their blades aren't designed to do that. Any decent compressor or tubine map comes with a pressure ratio and EFFICIENCY information. CFM is useless by itself.
Oh and last but not least, your funniest analogy. CARBs. HAHA.














Carbs operate purely in vacuum. There is no positive pressure. They operate in vacuum cause by the lowered static pressure caused by high velocity airflow through an orifice. Try putting a carb after a turbo and trying to get fuel to be sucked into the airflow under boost, good luck. A carb bases its fuel flow off of a difference in the fuel pressure head and static pressure in the venturi. They are rated in CFM because the flow accross them is assumed to fall in an arguably large range of temperatures and pressures. This is why a change in atmospheric pressure or temperature can cause lean or rich conditions in a carbed engine.
Can't we all just agree that volume flow through an engine is determined by the engine itself, not the compressor? And that density is what is important? And that density is directly proportional to temperature and pressure? I'm not just making this stuff up guys....people figured this out many, many, years ago.

_Modified by thom337 at 10:30 PM 8-28-2009_


_Modified by thom337 at 10:31 PM 8-28-2009_


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## 04VDubGLI (May 20, 2005)

*Re: (thom337)*

The point regarding carbs and air compressors and fans is not to compare them to turbos, but to explain that CFM ratings are what someone needs to understand the amount of air that some object can move. Again, a compressor map is only useful with information about the engine you're going to use the compressor on, but that doesn't change what the compressor itself is capable of. I guess more specifically with carbs as an example, they are able to provide fueling for that amount of air (not directly, but corratively). It has nothing to do with boost. That's sort of the point I've tried to make the entire time in some way - saying you run 20psi is useless information.


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## killa (Nov 26, 2000)

*Re: (04VDubGLI)*


_Quote, originally posted by *04VDubGLI* »_
How about we move on to discuss billet wheeled turbos then. Let's look at the HTA 3582 and regular 3582?
How about an explanation for why the BILLET 3582 makes more power than the regular 3582? Same turbine wheel... same turbine housing... same dimensions. Same car. Why does it make more power?








I guess I better get 4 k03s and make individual manifolds and run them all at 40psi. By far the best option. Oh, maybe I should get a huge turbine housing for each of those 4 as well. No matter what the compressor wheels STILL ARE RATED FOR LIKE 25 LB/MIN. Why is this such a difficult concept? They can only move so much air, period.

_Modified by 04VDubGLI at 11:02 PM 8-27-2009_

The billet compressor wheels are totally redesigned, they do not have the same compressor maps. Garrett engineers have recently re-made a GT40 compressor wheel out of billett with the same exact shape as the cast aluminum counterpart while the only thing different being the material and ended up with the same compressor map. 
Def. a good question though http://****************.com/smile/emthup.gif


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## thom337 (Oct 13, 2007)

*Re: (04VDubGLI)*


_Quote, originally posted by *04VDubGLI* »_The point regarding carbs and air compressors and fans is not to compare them to turbos, but to explain that CFM ratings are what someone needs to understand the amount of air that some object can move. 

Right, but all of your examples proved that using CFM alone to rate something is useless. Especially when comparing it to the realm of tubochargers. A compressor isn't "capable" of flowing a volumetric flow. It flows what the engine is flowing. 


_Quote, originally posted by *04VDubGLI* »_ Again, a compressor map is only useful with information about the engine you're going to use the compressor on, but that doesn't change what the compressor itself is capable of. 

HA. So how is rating a compressor in just CFM any different than looking at a compressor map with no idea what the engine conditions are? My entire argument is that you must fix the properties to get a real idea of performance. You get volume flow from engine speed and rpm, pressure from the pressure ratio, and temperature from the efficiency. 

_Quote, originally posted by *04VDubGLI* »_ I guess more specifically with carbs as an example, they are able to provide fueling for that amount of air (not directly, but corratively). 

Carbs do not provide air based on volume flow. They don't. They don't. They don't. Period. They provide fuel based on a velocity and a DENSITY. Volumetric flow is a velocity through an area. Static pressure is decreased by the square of velocity times one half the density. The fuel flow through a carb is regulated by the pressure differential between the fuel pressure head and the negative (with relation to atmosphere) pressure of the air flowing through it. JEGs / Summit / whoever else rates those so that retarded ******** can get a suitable carb for their 5L v-8 that revs to X rpm. 

_Quote, originally posted by *04VDubGLI* »_That's sort of the point I've tried to make the entire time in some way - saying you run 20psi is useless information. 

When did I say this was the only important information? Please point to it. I would love to see it. From the beginning I have said that DENSITY is what is important. This comes from pressure AND temperature. Mass flow comes from a volumetric flow (determined by engine displacement and rpm) at a certain DENSITY.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
Right, but all of your examples proved that using CFM alone to rate something is useless. Especially when comparing it to the realm of tubochargers. A compressor isn't "capable" of flowing a volumetric flow. It flows what the engine is flowing.
 Thomas... Your over thinking things to the point of being wrong.. As the rpms climb the intake and exhaust valves open and close faster. So fast in fact; that your sealed chamber theory goes out the window. This is what allows the turbo to shove more air and fuel through the combustion chanbers, get ignited and then pass out of the exhaust. This is why more cfm's = more power. Oversimplified of course. Its easy to get hung up on one or two parts of the equation, and make blanket statements. When all factors are considered your little theory that you like to throw around as a fact is null and void..

_Quote, originally posted by *thom337* »_ JEGs / Summit / whoever else rates those so that retarded ******** can get a suitable carb for their 5L v-8 that revs to X rpm. 

 This was an ignorant statement on your part. It takes a lot more knowledge about engines than you possess to properly set up a carburated engine. Its quite a bit more difficult in practice than you seem to think. Try syncing a trio of 2 barrel carbs one day with a set of mercury gauges.. Let me know how that works out for you. This particular statement proved to me that you don't have any practical experience at all.. Just equations, and theory. Which by themselves are useless without the practical experience to put them to work.. 

_Modified by The*Fall*Guy at 11:58 PM 8-28-2009_


_Modified by The*Fall*Guy at 6:08 AM 8-29-2009_


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## [email protected] (Jul 2, 2006)

*Re: (BoostinBejan)*


_Quote, originally posted by *BoostinBejan* »_
Think of it this way.
k03 at 15psi at 2000rpm on an engine.
GT30R at 15psi at 2000rpm on an engine.
same temp, same volume to fill, same engine, SAME POWER. The reason why you don't SEE that, is the fact that the k03 is falling off up top where the engine is most effecient, and the 30R keeps pushing.
edit- the engine doesn't know that it's a k03, or a 30r. As long as its pushing the same PSI through the intercooler piping, at the same RPM and same temperature, then you will have the exact same power.
_Modified by BoostinBejan at 2:18 PM 8-27-2009_


you cant compare the Ko3 at that boostlevel.
Its maxed out at 7psi and have already left the compressor chart







.
You need to get a 3071 or similar and compare that at 15psi


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## l88m22vette (Mar 2, 2006)

*Re: ([email protected])*

So wait, what does CFM stand for again?


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## thom337 (Oct 13, 2007)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_ Thomas... Your over thinking things to the point of being wrong.. As the rpms climb the intake and exhaust valves open and close faster. So fast in fact; that your sealed chamber theory goes out the window. This is what allows the turbo to shove more air and fuel through the combustion chanbers, get ignited and then pass out of the exhaust. This is why more cfm's = more power. Oversimplified of course. Its easy to get hung up on one or two parts of the equation, and make blanket statements. When all factors are considered your little theory that you like to throw around as a fact is null and void..


So....as RPM rises the ENGINE consumes more VOLUME air. This is why volume flow (CFM) is controlled entirely by the engine, and why it doesn't make sense to rate a compressor purely in CFM. I have no sealed chamber theory, charge density still applies even in transients and with pressure waves bouncing around in the intake. This is why you want to design proper runner lengths and plenum size, you want the peak DENSITY to occur in a runner when the valve is about to open. You get your highest density when you can create the highest pressure at the lowest temperature. 
Nothing I said is only valid in a "sealed chamber". 
A 1.8 liter engine at 5,000 rpm consumes half its displacement volume of air per cycle at 0 psi or at 4 million psi. As someone else put it, if I have 1 liter of air at 100psi, how many liters of air do I have? You guys can keep on reading your compressor maps to "figure out how many cfm you can flow", but you are not helping yourselves.

_Quote, originally posted by *The*Fall*Guy* »_ 
This was an ignorant statement on your part. It takes a lot more knowledge about engines than you possess to properly set up a carburated engine. Its quite a bit more difficult in practice than you seem to think. Try syncing a trio of 2 barrel carbs one day with a set of mercury gauges.. Let me know how that works out for you. This particular statement proved to me that you don't have any practical experience at all.. Just equations, and theory. Which by themselves are useless without the practical experience to put them to work.. 


The person who brought up carbs was using them as an example of why CARBs rationalize rating things in purely CFM. I simply showed why this is completely untrue. Please show me how anything I said in my post was ignorant, I believe I explained exactly how they function, and exactly why they are undesirable. I also explained why they are often times rated in CFM, and why this has no bearing on our discussion of turbocharger compressors.
CARBs are old technology....cool technology,yes....but old and outdated. There is absolutely no comparision in mixture control between today's EFI systems and CARBs. If it makes you feel better to talk about all the CARBed cars you set up, you can. Turbocharger performance is still dictated by charge density.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (thom337)*

Quite simple Thomas... I was reffering to your ******* comment. I grew up with a family that was heavily involved in proffessional drag racing. My stepfather raced top fuel funny cars back in the day. A couple of his friends raced pro-stock door slammers. The pro- stock guys are extremely intelligent when it comes to carbs. On a more personal note I myself spent quite a bit of time working on carbed muscle car engines. Although my heart lies with modern vag tech I have a ton of respect for the knowledge that it takes to properly set up a carbed engine. Calling these guys ******** is an undeserved insult of the highest order. Although you may be technicly correct in a couple of your points they have no basis in reality. Reality is what matters when tuning any engine for performance. Its not all about math and theory. Its a big part of it, but not the whole story when it comes to actually putting ideas into practice.. You have even argued with Arnold at Pag.. A guy who really knows his ish. 


_Modified by The*Fall*Guy at 9:22 AM 8-29-2009_


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## thom337 (Oct 13, 2007)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_Quite simple Thomas... I was reffering to your ******* comment. 


Seriously man....call the wambulance. For what its worth, I would consider myself to be a *******...to people who are ******** its not exactly a derogatory term, most people love it haha. Also, why are you now addressing me with my real name in all of your posts? Do you know me?

_Quote, originally posted by *The*Fall*Guy* »_The pro- stock guys are extremely intelligent when it comes to carbs. 


Did I ever say that they weren't? There are some technically brilliant people in NASCAR who know how to manipulate carbs in brilliant ways. I love how you took my statement that rating CARBs in CFM had no bearing on rating a turbo in CFM and took it to mean that everyone who ever saw/ used/ designed a carburetor is stupid. Again, how does this apply to the discussion at hand?

_Quote, originally posted by *The*Fall*Guy* »_ Although you may be technicly correct in a couple of your points they have no basis in reality. Reality is what matters when tuning any engine for performance. Its not all about math and theory. Its a big part of it, but not the whole story when it comes to actually putting ideas into practice.. You have even argued with Arnold at Pag.. A guy who really knows his ish. 


My points have completely relevance in reality. You still cannot provide an example for why rating a compressor in purely CFM has any real value in the practice or principle. People don't just pull math and physics equations out of their butt. They are derived from observations and testing. 
You point about Arnold is laughable. OH NOES! I ARGUED WITH ARNOLD! Debate is what spurs people to learn new things, if you don't like the fact that me and Arnold were having a good technical discussion, don't go to a technical forum. You can't just tell me I'm wrong purely because I was arguing with Arnold, that is about the silliest logic I have ever heard of.


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## engineerd18t (Dec 12, 2007)

I didn't read the last couple of pages but try reading through this. All you care about is more fuel burned more efficiently per unit time. I should get back into this paper but these are just the basics.
http://users.wpi.edu/~bbeach/E...1.pdf


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## dubchuck117 (Feb 6, 2009)

*Re: (thom337)*

thom337 you say that a larger turbo raises efficiency by lowering temps at the same psi, which i agree with. but youre saying cfm have no effect on power. i dont agree with this at all. think about it if you make the air colder its going to be denser (another point of yours). but if you make a given volume of air denser, would it still take up the same amount of space as its less dense state? i dont think so. and i also dont think a turbo is going to let this extra space go unused. it will be filled with more dense air, meaning more cfms, right?


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## thom337 (Oct 13, 2007)

*Re: (dubchuck117)*


_Quote, originally posted by *dubchuck117* »_thom337 you say that a larger turbo raises efficiency by lowering temps at the same psi, which i agree with. but youre saying cfm have no effect on power. i dont agree with this at all. think about it if you make the air colder its going to be denser (another point of yours). but if you make a given volume of air denser, would it still take up the same amount of space as its less dense state? i dont think so. and i also dont think a turbo is going to let this extra space go unused. it will be filled with more dense air, meaning more cfms, right?

A larger turbo can create a lower temperature charge because of higher efficiency. CFM alone has no effect on power. A k03 @ 1 psi @ 5,000 rpm is pumping the same CFM into the engine as a GT-4088 @ 30 psi @ 5,000 rpm. The disparity between the two is density, not volume flow. the higher density alllows for a higher mass flow at the same volume flow, and therefore greater power. The engine controls volume flow, you cannot fill more volume than the engine has volume to fill. CFM by itself means nothing.


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## bigT1.8t (Mar 23, 2009)

so your saying volume cannot be increased by increasing the pressure. I tell a what, lets take a 12 gram c02 canister. normally it can fit x amount of air at ambient temperatureand pressure. but when you pressurize that air at 850psi inherently there is more air inside the canister. now take that canister, put a big balloon over it and release the air. The balloon will fill with a greater volume than what was in the canister because the pressure is reduced. the only way you can stop adding air or c02 or what have you is when it liquefies and fills the space. so you can fit more air into a given space by adding pressure. 
This thread needs to be black holed
_Modified by bigT1.8t at 12:18 PM 8-29-2009_


_Modified by bigT1.8t at 12:21 PM 8-29-2009_


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## thom337 (Oct 13, 2007)

*Re: (bigT1.8t)*


_Quote, originally posted by *bigT1.8t* »_so your telling me that the ko4 at 1psi and the 4088 at 30psi in your example would draw in the sameair flow past the maf? in order to create denser air you must have more air to compress. Temperature alone will not create that density difference. the only was this would happen is if you went from 200f to below zero. The compression factor regarding tempdifference simply isn't there. therefore there must be a greater reading past the maf. 
This thread needs to black holed. 


We're talking about post compressor flow. In any event, the flow past the MAF is at atmospheric density, so for mass flow to be equal in and out of the compressor, the volumetric (cfm) flow through the MAF is of course higher if a turbo is flowing a greater mass flow in comparison to another. Anyways, compressor maps are not rating the suction side of the compressor, if they were there would be no pressure axis. Rating a compressor in purely CFM is effectively telling you nothing about its performance.
And yes, if a pressure is maintained and the temperature is dropped, the increase in density will be directly proportional to the temperature drop. I didn't make this up...it just is. 
Why again should this be blackholed?


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## bigT1.8t (Mar 23, 2009)

because there has been no agreement only arguing for five pages. and i have edited that post


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## dubchuck117 (Feb 6, 2009)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
We're talking about post compressor flow. *In any event, the flow past the MAF is at atmospheric density, so for mass flow to be equal in and out of the compressor, the volumetric (cfm) flow through the MAF is of course higher if a turbo is flowing a greater mass flow in comparison to another. *Anyways, compressor maps are not rating the suction side of the compressor, if they were there would be no pressure axis. Rating a compressor in purely CFM is effectively telling you nothing about its performance.
And yes, if a pressure is maintained and the temperature is dropped, the increase in density will be directly proportional to the temperature drop. I didn't make this up...it just is. 
Why again should this be blackholed?

either you just proved yourself wrong or turbos create air i can't figure it out


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## thom337 (Oct 13, 2007)

*Re: (bigT1.8t)*


_Quote, originally posted by *bigT1.8t* »_so your saying volume cannot be increased by increasing the pressure.


I'm saying that increasing the pressure of a compressor is not increasing the volume flow out of it. It is increasing the MASS flow out of it.

_Quote, originally posted by *bigT1.8t* »_ so you can fit more air into a given space by adding pressure. 
This thread needs to be black holed


You can fit more mass air into the space by increasing the pressure, but you cannot increase the volume flow to more volume than there is volume to fill, unless you have a non rigid container like a balloon. Let me know the next time you hit boost and your cylinders start expanding to allow for more volume flow. 
I still don't think any of you understand what VOLUME is. Its nothing more than a 3 dimensional space. A compressor map is showing what is happening at the EXIT of the compressor. The compressor does not get to pick the volume it is flowing into, this is fixed by the volumetric consumption of the engine. 
Once again, an example: Two turbos are each operating on a 1.8L engine at 4,000 rpm. They both have IDENTICAL VOLUME FLOW. One of the turbos is a GT4088 and is at 20 psi with relatively low air temps, the other is a K03 at 5 psi with relatively high intake temps. The 4088 is SUCKING in a greater VOLUME of atmospheric air, but they are both delivering to the engine the EXACT SAME VOLUMETRIC FLOW. The performance increase of the 4088 comes from the fact that its volume flow is at a much, much great DENSITY. You can have two identical volumetric flows, and they can have completely different MASS flows.


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## thom337 (Oct 13, 2007)

*Re: (dubchuck117)*


_Quote, originally posted by *dubchuck117* »_
either you just proved yourself wrong or turbos create air i can't figure it out










You just can't read. Mass flow is conserved in and out of the turbo. 
Volume flow at the outlet is fixed by the engine. 
The volume flow INTO the compressors is different if they have different mass flows. 
The volume flow OUT of the compressors is controlled by the engine. 
Compressor maps are showing the flow at the compressor exit.
They make power by accelerating a high volume of atmospheric air, and stagnating it into a lower volume airflow into the engine, causing a pressure rise which increases the DENSITY of the air filling the fixed volume of the engine. This increase in density of the fixed volume flow results in a higher mass flow, which lets you create more power by burning more fuel.


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## NOLA_VDubber (May 24, 2007)

*Re: (thom337)*

damn thom, i don't know how you do it. I would have given up a long long time ago. I guess you can use this time to freshen up for the PE exam if you haven't already taken it yet


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## thom337 (Oct 13, 2007)

*Re: (NOLA_VDubber)*


_Quote, originally posted by *NOLA_VDubber* »_damn thom, i don't know how you do it. I would have given up a long long time ago. I guess you can use this time to freshen up for the PE exam if you haven't already taken it yet









Just got my results last week actually. Passed!


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## The*Fall*Guy (Aug 10, 2009)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
A 42r and K03 both at the same boost pressure, at the same rpm, with the same manifold temperature will produce the same mass flow of air. They will and they do.

So... According to thom337 the 1.8t forum's new guru.. The cfm of your turbo doesn't matter. We can all just stick with the k03s and make big power.. Boost is boost.. So as soon as I get my Maestro software I'm gunning for 400whp on my k03s.. Bob Q.. Look out..










_Modified by The*Fall*Guy at 5:30 PM 8-29-2009_


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## bigT1.8t (Mar 23, 2009)

does that mean i have to build my motor with my k04? lol
im thinkin 500 wheel!!! wohooo


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## The*Fall*Guy (Aug 10, 2009)

*Re: (bigT1.8t)*

Correct... Except now that I think about it. I might as well just run a ko4-023 and gun for 600whp..
Honestly.. I'm glad Thomas stepped in and offered his wealth of knowledge. I was about to waste a ton of cash on hardware I don't even need.


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## [email protected] (Oct 23, 2008)

*Re: (The*Fall*Guy)*

Dont worry guys. I dont think the physics and characteristics in what each and every turbo offers isnt completely dictated by the engine. The turbos have something to contribute to this whole equation. You can see it in the boost curves, surge points, fluttering, bov and wastegate springs boost controller settings,etc etc, needed per application. Each turbo must be set up differently on the SAME engine. Some would say its due to the restriction of the engine, which plays a role until you see the disparity in the boost plots. What do you know? The turbo cfm which speeds up and increases density/time actually controls the boost/rpm plot! What a novel idea!


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## The*Fall*Guy (Aug 10, 2009)

*Re: ([email protected])*

Sorry Arnold... But "Thomas" has filled up several pages explaining how we can make the same power at the same boost level with a small turbo... He even used some really big words, and posted an equation or two.. He must be right.. And this whole time I was gearing up to drop some serious coin on one of your 30r setups.. Call me misguided


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## [email protected] (Oct 23, 2008)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_Sorry Arnold... But "Thomas" has filled up several pages explaining how we can make the same power at the same boost level with a small turbo... He even used some really big words, and posted an equation or two.. He must be right.. And this whole time I was gearing up to drop some serious coin on one of your 30r setups.. Call me misguided









Well, he's not entirely wrong on the subject. For a few hundred rpm's, it'll inevitably cross somewhere. I just dont like the 'cfm doesnt matter' bit... experience does count for something. I was one of those guys fresh out of school, ready to conquer the world too... I mean, these guys on another thread were testing compressive loads at 45deg angles on rods when there's nothing but tensile load at that position. But, I guess they were proving a hypothetical point... Reality and actual applied effort humbles us all...


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## The*Fall*Guy (Aug 10, 2009)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
Well, he's not entirely wrong on the subject. For a few hundred rpm's, it'll inevitably cross somewhere. I just dont like the 'cfm doesnt matter' bit...
 yes. I agree with that point myself. But it has no basis in reality.. And for the record. The whole cfm doesn't matter part is what drives me nutz.. I'm a builder by trade. And when I argue with this guy its like I'm arguing with an architect that I hired who just doesn't get it.. It doesn't matter if it works on paper. If it doesn't work, or is impossible to achieve in practice. Who cares? This whole argument is meaningless.. It reminds me of when Bill Clinton questioned the meaning of the word "is" during the Lewinski scandal.. Its all wordplay.. It means nothing in reality..


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## Agtronic (May 14, 2001)

*Re: (The*Fall*Guy)*

But you guys don't understand. What he is saying is 100% true. And not once in this entire thread did he say a K03 would make the same power as a GT30. The bit about CFM not mattering is completely accurate. 
You guys are not listening to the main point of the discussion, which is that there are OTHER reasons why larger turbos make more power, and it IS NOT because the larger compressor "forces" more CFM down the engine's throat.
No one is saying that flow maps mean nothing.
No one is saying that flor ratings mean nothing.
No one is saying big turbos make the same power as little ones.
There is nothing here that works on paper, and does not work in the real world. Volume entering the motor does not change no matter WHAT compressor you are running.
killa just summed up everything thom337 said, to the T.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (Agtronic)*

Ummm... No.. I do understand the many variables involved.. And CFM is important, as well as efficiency, hotside flow, etc... We all know this.. No news here.. The point is.. "Thomas" is going on for several pages about nothing.. There is zero point to any of this.. Either he is trying to tell us that size doesn't matter or he is just wasting away his fingertips on the keyboard for nothing.. Who cares if two different turbos will make the same power for 50rpm acrossed the entire band.. It doesn't matter. This knowledge doesn't help with tuning either.. Totally pointless.. Its all about "Thomas" trying to cry to the world at the top of his lungs that he is right.... And he is right. On a minor technicality that means nothing to anyone except the guy arguing it. 
CFM matters... Period..


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## bigT1.8t (Mar 23, 2009)

see? i was right! this thread needs to be black holed! lol 
But seriously, he was right in the fact that at some point along the curve the two would cross but cfm does matter. 
And now that were all friends again what should we talk about? lol


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## The*Fall*Guy (Aug 10, 2009)

*Re: (bigT1.8t)*

Blackholed?? Nah... Its a great place to blow off steam without interrupting the rest of the forum.. Yes he was correct.. About something that means nothing.. Noone learned anything from this.. Almost every guy that argued in this thread previously knew enough to make an informed decision about choosing the proper sized turbo, etc.. Re-read it.. Its several pages of "Our Hero" getting his panties in a bunch over a technicality that means nothing to anyone, ever.. 
If anything this little technicality would just confuse a newbie into making the wrong choice for his power goals..
But again.. I hear a bench grinder humming away as our hero sharpens up his sliderule for yet another round.....


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## iThread (Sep 27, 2005)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_Blackholed?? Nah... Its a great place to blow off steam without interrupting the rest of the forum.. 

Exactly, and so far I think this is going well. If you folks want to use this topic to just discuss 1.8T stuff in general feel free, it's your forum. Just don't let it get out of hand and try and keep the topics 1.8T related.
Sound good?


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## Agtronic (May 14, 2001)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_Ummm... No.. I do understand the many variables involved.. And CFM is important, as well as efficiency, hotside flow, etc... We all know this.. No news here.. The point is.. "Thomas" is going on for several pages about nothing.. There is zero point to any of this.. Either he is trying to tell us that size doesn't matter or he is just wasting away his fingertips on the keyboard for nothing.. Who cares if two different turbos will make the same power for 50rpm acrossed the entire band.. It doesn't matter. This knowledge doesn't help with tuning either.. Totally pointless.. Its all about "Thomas" trying to cry to the world at the top of his lungs that he is right.... And he is right. On a minor technicality that means nothing to anyone except the guy arguing it. 
CFM matters... Period..

I agree that the technicalities mean very little in what we are doing here. Bolting turbos to engines to make more power is how we've been doing it for a long time, and that's not going to change with the info in this thread.


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## thom337 (Oct 13, 2007)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_So... According to thom337 the 1.8t forum's new guru.. The cfm of your turbo doesn't matter. We can all just stick with the k03s and make big power.. Boost is boost.. So as soon as I get my Maestro software I'm gunning for 400whp on my k03s.. Bob Q.. Look out..










Please point to one place in this thread where I said that. I like how you prove yourself completely wrong then start saying I am hurting ********' feelings and that I'm saying we can all make 400whp on a K03 turbo, you have no factual argument to make so you are behaving like a 5 year old before bedtime. Grow up. If it makes you feel better to say that I said things I didnt, have fun. No one on here knows who I am, I'm not out to impress anyone, I was just trying to attempt to correct a big misconception on this forum. I am not seeking anyones approval, much less the approval of someone who has demonstrated such little knowledge from so much "practical experience". 
Boost is not boost when it occurs at different conditions. Boost alone means nothing about performance. 
Boost, at an RPM, at a temperature. That means something. Because its a MASS flow, and air mass is what makes power. 
CFM still doesn't mean anything by itself. Two flows of the exact same CFM can have radically different mass flows, mass flow makes power. Please dispute this incredibly basic idea. 


_Quote, originally posted by *bigT1.8t* »_does that mean i have to build my motor with my k04? lol
im thinkin 500 wheel!!! wohooo









Again for all the 4 year olds who didn't read the thread. I never said that. I said that a small turbo whose charge has been sufficiently cooled, when operating at the same pressure, temp, and RPM as a larger turbo, will be feeding the same air mass into the engine. 

_Quote, originally posted by *The*Fall*Guy* »_Correct... Except now that I think about it. I might as well just run a ko4-023 and gun for 600whp..
Honestly.. I'm glad Thomas stepped in and offered his wealth of knowledge. I was about to waste a ton of cash on hardware I don't even need.









Again, grow up. I never said that a k04-023 makes 600whp. The only turbo comparisons I made were to illustrate the importance of charge density. I even specifically said several times that we all know larger turbos make more power, I was just trying to get at the root of why.

_Quote, originally posted by *[email protected]* »_Dont worry guys. I dont think the physics and characteristics in what each and every turbo offers isnt completely dictated by the engine. Some would say its due to the restriction of the engine, which plays a role until you see the disparity in the boost plots. What do you know? The turbo cfm which speeds up and increases density/time actually controls the boost/rpm plot! What a novel idea!

I never said that the physics and characterstics of every turbo is dictated by the engine. Please, please, please show me where I said that. I said that the VOLUME FLOW out of the compressor is dictated by the volumetric flow rate of the engine. 
The compressor exit cfm can not be higher than the engine's volumetric flowrate, period (unless you are both feeding the engine and dumping air to somwhere else). It is pumping INTO the engine. It is raising the pressure of the volumetric flowrate entering the engine, increasing the mass flow. 
I am not disagreeing that at the SUCTION side of the turbo, a large volumetric flow of atmospheric air is entering the compressor...but at the compressor outlet it can only pump into the space of the engine.

_Quote, originally posted by *The*Fall*Guy* »_Sorry Arnold... But "Thomas" has filled up several pages explaining how we can make the same power at the same boost level with a small turbo... He even used some really big words, and posted an equation or two.. He must be right.. And this whole time I was gearing up to drop some serious coin on one of your 30r setups.. Call me misguided









Again, you do not offer any sort of factual argument. You just make up stuff I didn't say because you don't have any idea what is going on. 

_Quote, originally posted by *[email protected]* »_
Well, he's not entirely wrong on the subject. For a few hundred rpm's, it'll inevitably cross somewhere. I just dont like the 'cfm doesnt matter' bit... experience does count for something. I was one of those guys fresh out of school, ready to conquer the world too... I mean, these guys on another thread were testing compressive loads at 45deg angles on rods when there's nothing but tensile load at that position. But, I guess they were proving a hypothetical point... Reality and actual applied effort humbles us all...

The point of my original statement was not that a k03 can make the same mass flow as a GT-4088 at a certain condition. The point of my original statement was to say that compressors should be viewed as... compressors, increasing the density of air in order to make power. 
Again, I stand by the statement that CFM by itself means nothing. You show me one turbo that flows X cfm and I'll show you another one that flows X cfm but does it at a completely different pressure and efficiency. CFM is x axis on a compressor map, we are specifying that value and then dictating the others to get an idea of performance because the ENGINE is specific the volumetric flowrate operating point.
This is entirely relevant. It makes people think about what is really making power. Slapping a CFM label on a turbo, or carefully considering the effects of charge cooling and increasing boost so that you can obtain the highest possible density in the manifold.

_Quote, originally posted by *The*Fall*Guy* »_ yes. I agree with that point myself. But it has no basis in reality.. And for the record. The whole cfm doesn't matter part is what drives me nutz.. I'm a builder by trade. And when I argue with this guy its like I'm arguing with an architect that I hired who just doesn't get it.. It doesn't matter if it works on paper. If it doesn't work, or is impossible to achieve in practice. Who cares? This whole argument is meaningless.. It reminds me of when Bill Clinton questioned the meaning of the word "is" during the Lewinski scandal.. Its all wordplay.. It means nothing in reality..









All of this stuff I have been talking about works on paper and in practice and I have done it, seen it, put thermocouples on it and tested it...dynoed it, tracked it, timed it, logged it. 
Again....since saying CFM doesn't matter drives you crazy....I said cfm BY ITSELF is useless, not that CFM has no meaning, or does not matter in any way.
The point is to increase manifold density, so that during cylinder filling you get more air molecules in the cylinder and you make more power, period. Looking at a turbo by means of CFM only is NOT the way to do this. You can keep doing it wrong, that is fine with me. I am not here to defend myself, I was just trying to correct the misinformation floating around on this forum. 

Anyways, this is my last post in this thread. Unless you guys decide to have a factual conversation about something, preferably another topic. If anyone wants to talk about this more, we can do it over PM or e-mail or whatever. People's ego's get in such a bunch when you discuss things in a public place. 
Alas, I will leave this thread sticking to my guns and waiting for someone to tell me why two equal volume flows of different density will create the same mass flow, please let me know when you figure it out.
Have fun everyone.


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## [email protected] (Oct 23, 2008)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
I never said that the physics and characterstics of every turbo is dictated by the engine. Please, please, please show me where I said that. I said that the VOLUME FLOW out of the compressor is dictated by the volumetric flow rate of the engine. 
The compressor exit cfm can not be higher than the engine's volumetric flowrate, period (* unless you are both feeding the engine and dumping air to somwhere else*). It is pumping INTO the engine. It is raising the pressure of the volumetric flowrate entering the engine, increasing the mass flow. 
I am not disagreeing that at the SUCTION side of the turbo, a large volumetric flow of atmospheric air is entering the compressor...but at the compressor outlet it can only pump into the space of the engine.

 
You see, what you're saying is contradictory. If it cannot go higher, why would it need to dump air anywhere? You said you understand surge and backflow.. I wonder if you really do... I understand that the reason it does this is that IT cant go anywhere else as its reached its volumetric capacity







(happy?) But the compressor can TRY and it does in certain conditions. What do you do in this case? Try to raise the VE of the motor or exhaust side (heh, sometimes its not even the engine) if there is a bottleneck... So, sometimes its dictated by the turbo...

_Quote, originally posted by *thom337* »_
The point of my original statement was not that a k03 can make the same mass flow as a GT-4088 at a certain condition. The point of my original statement was to say that compressors should be viewed as... compressors, increasing the density of air in order to make power. 
Again, I stand by the statement that CFM by itself means nothing. You show me one turbo that flows X cfm and I'll show you another one that flows X cfm but does it at a completely different pressure and efficiency. CFM is x axis on a compressor map, we are specifying that value and then dictating the others to get an idea of performance because the ENGINE is specific the volumetric flowrate operating point.


Compressors dont just increase, but maintains, surpasses and initiates as well. This is where the smaller wheel and larger wheel has disparities.
CFM by itself doesnt mean much, i agree. But volumetric efficiency is also a piece to the puzzle as well.


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## bigT1.8t (Mar 23, 2009)

AHAHAHAHA!!!!!! ouch, that stung LOL
ive read every post you've made since page 1 and i have yet to see anything that hasn't had holes shot through it so im going to ignore your posts for now on (unless you really insult me) so ill only be looking at those replies that have some degree of reality in them. ill give you credit though, the four year old comment was pretty good


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## killa (Nov 26, 2000)

*Re: (bigT1.8t)*


_Quote, originally posted by *bigT1.8t* »_so your saying volume cannot be increased by increasing the pressure. I tell a what, lets take a 12 gram c02 canister. normally it can fit x amount of air at ambient temperatureand pressure. but when you pressurize that air at 850psi inherently there is more air inside the canister. now take that canister, put a big balloon over it and release the air. The balloon will fill with a greater volume than what was in the canister because the pressure is reduced.


The volume would be the same but the amount of air (compressed) would be bigger because you just raised pressure roughly 58.5 times
Releasing the air from the balloon would bring the pressure down a whole lot and increase the volume of the balloon.
Pressure = Force / Area, if Force changes then the area must change as well to keep pressure constant.
Compressor cfm is important to hold volume needed to get a certain psi. I can use a 40R in a [email protected] to hold a constant, cool charge and have a nice sized turbine wheel to get rid of the backpressure. that a 2.8L motor at roughly 3 bar can produce. You can't do that with a k03 as the compressor can't keep up with the amount of air needed to keep a [email protected] psi efficiently and its turbine wouldn't be able to get rid of the backpressure, egt's would also go to a never seen number.

Hope this helps clearing things up http://****************.com/smile/emthup.gif


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## [email protected] (Oct 23, 2008)

*Re: (Agtronic)*


_Quote, originally posted by *Agtronic* »_But you guys don't understand. What he is saying is 100% true. And not once in this entire thread did he say a K03 would make the same power as a GT30. The bit about CFM not mattering is completely accurate. 
You guys are not listening to the main point of the discussion, which is that there are OTHER reasons why larger turbos make more power, and it IS NOT because the larger compressor "forces" more CFM down the engine's throat.
No one is saying that flow maps mean nothing.
No one is saying that flor ratings mean nothing.
No one is saying big turbos make the same power as little ones.
There is nothing here that works on paper, and does not work in the real world. Volume entering the motor does not change no matter WHAT compressor you are running.
killa just summed up everything thom337 said, to the T.

No one says that it FORCES more cfm down the engine's throats. But CFM's dictate efficiency at points in the compressor map which correlates w/ the VE of whatever engine.
Killa was here yesterday. He's a good buddy. He knows that what he said or quoted isnt entirely correct either..


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## killa (Nov 26, 2000)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
No one says that it FORCES more cfm down the engine's throats. But CFM's dictate efficiency at points in the compressor map which correlates w/ the VE of whatever engine.
Killa was here yesterday. He's a good buddy. He knows that what he said or quoted isnt entirely correct either..

I Quoted Tony1 and agreed to most of it. I've added my opinion right before you posted man lol.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (killa)*


_Quote, originally posted by *killa* »_
Compressor cfm is important to hold volume needed to get a certain psi. I can use a 40R in a [email protected] to hold a constant, cool charge and have a nice sized turbine wheel to get rid of the backpressure. that a 2.8L motor at roughly 3 bar can produce. You can't do that with a k03 as the compressor can't keep up with the amount of air needed to keep a [email protected] psi efficiently and its turbine wouldn't be able to get rid of the backpressure, egt's would also go to a never seen number.

Hope this helps clearing things up http://****************.com/smile/emthup.gif 
 this is the exact point that everyone, including Arnold was trying to get acrossed to thom337.. Well put


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## [email protected] (Oct 23, 2008)

*Re: (killa)*


_Quote, originally posted by *killa* »_
I Quoted Tony1 and agreed to most of it. I've added my opinion right before you posted man lol.


Did you say you had a laptop w/ a parallel port? I tested out my power pins and am getting a meek 3.3v output which is pissing me off. I need 5v output to control the cnc... dont want to use a PC and i cant use an express or PCMCIA converter to control my post processor on this damn fancy drill!!


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## killa (Nov 26, 2000)

I think we're all agreeing on the same points:
1)You can't shove more air inside of the same displacement motor without raising psi
2)A larger compressor will be more efficient, I've added that it's also because a larger compressor doesn't need to spin as hard as a small compressor to move the amount amount of air
3) I've also added that most people here overlooked the turbine side, you need a large turbine to keep up with the large compressor since a small turbine will add more shaft speed at lower rpm's causing the compressor to surge and the turbine to choke up.
What don't we agree on? Larger turbos can put more air inside of the same engine at the same rpm? That's simply not true but they however allow to keep up with the engine's needs while keeping the whole compressor/turbine combination efficient. Do we all agree on this?


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## killa (Nov 26, 2000)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
Did you say you had a laptop w/ a parallel port? I tested out my power pins and am getting a meek 3.3v output which is pissing me off. I need 5v output to control the cnc... dont want to use a PC and i cant use an express or PCMCIA converter to control my post processor on this damn fancy drill!!

And you want to rely on a laptop that was made when windows 98 were around????


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## [email protected] (Oct 23, 2008)

*Re: (killa)*


_Quote, originally posted by *killa* »_I think we're all agreeing on the same points:
1)You can't shove more air inside of the same displacement motor without raising psi
2)A larger compressor will be more efficient, I've added that it's also because a larger compressor doesn't need to spin as hard as a small compressor to move the amount amount of air
3) I've also added that most people here overlooked the turbine side, you need a large turbine to keep up with the large compressor since a small turbine will add more shaft speed at lower rpm's causing the compressor to surge and the turbine to choke up.
What don't we agree on? Larger turbos can put more air inside of the same engine at the same rpm? That's simply not true but they however allow to keep up with the engine's needs while keeping the whole compressor/turbine combination efficient. Do we all agree on this?

I'll agree w/ most of that. But surge is sometimes caused by engines/engine parts as well. Small ports/runners vs. more efficient exhaust. You free this up, surge gone (well, maybe you might get it lower now as in your example 3 on certain turbos). This is the kind of compressor surge you feel upstairs rather then lower in the rpm band.
But yeah, any compressor cant physically force the engine to go beyond its limits


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## [email protected] (Oct 23, 2008)

*Re: (killa)*


_Quote, originally posted by *killa* »_
And you want to rely on a laptop that was made when windows 98 were around????









I dont need the bells and whistles, but at least 2000 professional would be nice


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## The*Fall*Guy (Aug 10, 2009)

*Re: (thom337)*

You love to quote everyone so much... How do you like it?

_Quote, originally posted by *thom337* »_, 
Again, you do not offer any sort of factual argument. You just make up stuff I didn't say because you don't have any idea what is going on.

 again. its ok for you to insult myself and others as you see fit. You can dish it out but you cant take it

_Quote, originally posted by *thom337* »_, 
The point of my original statement was to say that compressors should be viewed as... compressors, increasing the density of air in order to make power. 
 we had you at hello.

_Quote, originally posted by *thom337* »_, I stand by the statement that CFM by itself means nothing. 

What is your point? Any of the many factors involved mean nothing by themselves. This is your favorite point isnt it?

_Quote, originally posted by *thom337* »_
All of this stuff I have been talking about works on paper and in practice and I have done it, seen it, put thermocouples on it and tested it...dynoed it, tracked it, timed it, logged it. 
 I doubt this highly. If a guy like you had said logs on file you wouldve posted them.

_Quote, originally posted by *thom337* »_
Again....since saying CFM doesn't matter drives you crazy....I said cfm BY ITSELF is useless, not that CFM has no meaning, or does not matter in any way.
Again... You are mincing words.. What are you? An attorney?

_Quote, originally posted by *thom337* »_
I am not here to defend myself, I was just trying to correct the misinformation floating around on this forum. 

There were quite a few people in this thread besides yourself who knew what they were talking about. You stepped on them too..

_Quote, originally posted by *thom337* »_
Anyways, this is my last post in this thread. Unless you guys decide to have a factual conversation about something, preferably another topic. If anyone wants to talk about this more, we can do it over PM or e-mail or whatever. People's ego's get in such a bunch when you discuss things in a public place.









The only person in here "getting there ego in a bunch" is you. We have 6 pages of your rants, insults, and know it all cocky attitude to prove it.


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## coreyj (Aug 18, 2006)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
Again for all the 4 year olds who didn't read the thread. I never said that. I said that a small turbo whose charge has been sufficiently cooled, when operating at the same pressure, temp, and RPM as a larger turbo, will be feeding the same air mass into the engine. 


so your saying a ko4 at Sub zero temperature can make the same power as a 30r at ambient temperature. at the same pressure, engine speed, fueling, etc..?? 
What about the inlet diameter of the turbos? the 30r is going to pull in a bigger area of air than the ko4. the ko4 would have to spin at a higher velocity to pull in the same area of air as the 30r would.

even if the ko4 intake was at sub zero temperature to make the same power as a 30r at 7000rpm the velocity of the air coming into the inlet of the ko4 would have to be well beyond supersonic and the back pressure on the turbine would be too great. not to mention that this would have to be around 50psi and im not even sure if c16 gas could support that, (even though its all irrelevant because the ko4 would rip itself apart, and would not be able to support tthe pressure because of the extreme backpressure) and this would all have to be the same timing curve, to keep in line with your theory. these small turbos are not capable of working in the manner you are describing. end of story












_Modified by coreyj at 11:45 AM 8-30-2009_


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## Agtronic (May 14, 2001)

These technical thread always end the same way. Everyone starts posting "that's what we've been trying to say the whole time" and everyone agrees that they all had the same point to make, but in different words. In the end, nothing that thom337 said has gotten "holes shot through it". I'm not trying to nutswing or anything like that, but it's important that people realize what he has been saying is still correct. I admit he may have gotten too technical about it, which confused everyone more, or made the main point hard to see.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (Agtronic)*


_Quote, originally posted by *Agtronic* »_These technical thread always end the same way. Everyone starts posting "that's what we've been trying to say the whole time" and everyone agrees that they all had the same point to make, but in different words. In the end, nothing that thom337 said has gotten "holes shot through it". I'm not trying to nutswing or anything like that, but it's important that people realize what he has been saying is still correct. I admit he may have gotten too technical about it, which confused everyone more, or made the main point hard to see.
I understood every word he said... he tryed separating everything and attempted to prove that nothing was related.. unless of course he said it. Then the correlation made all the sense in the world. Carefully re-read everything he said. he contradicted himself all over the place. He got hung up on the deffinition of a couple words, and used this as a reason to insult everyones intelligence...


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## [email protected] (Oct 23, 2008)

*Re: (Agtronic)*


_Quote, originally posted by *Agtronic* »_These technical thread always end the same way. Everyone starts posting "that's what we've been trying to say the whole time" and everyone agrees that they all had the same point to make, but in different words. In the end, nothing that thom337 said has gotten "holes shot through it". I'm not trying to nutswing or anything like that, but it's important that people realize what he has been saying is still correct. I admit he may have gotten too technical about it, which confused everyone more, or made the main point hard to see.

Nothing confusing about what he said. On the contrary, its overly simplified


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## mescaline (Jul 15, 2005)

*Re: (The*Fall*Guy)*

thom,
explain this situation to me:
We take a balloon, fill it up with 2 liters of air and measure mass of it, air temperature is say 50C, we can agree that mass of this air will be constant right? Even if we put it in the fridge and cool it down to 10C, balloon will just shrink but will have the same mass right?
(This is why my football ball once exploded because it was on the sun for too long







)
Using water/methanol I can get K03S pushing 15 psi of air inside the engine at 40C / 5000rpm and I can certainly get GT35 pushing 15 psi of air nside the engine at 40C / 5000rpm.
Why is GT35 making more (read double) power?


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## 04VDubGLI (May 20, 2005)

Off topic, this has to be one of the most popular/most posted threads on Vortex. http://****************.com/smile/emthup.gif We are all winners now








I still feel how I feel about the topic though. I did use very simplified examples on how to explain why certain situations would/wouldn't work. And I also tried to even go outside of the turbo realm to bring in even more simplified concepts.


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## BoostinBejan (Apr 13, 2009)

*Re: (mescaline)*


_Quote, originally posted by *mescaline* »_thom,
explain this situation to me:
We take a balloon, fill it up with 2 liters of air and measure mass of it, air temperature is say 50C, we can agree that mass of this air will be constant right? Even if we put it in the fridge and cool it down to 10C, balloon will just shrink but will have the same mass right?
(This is why my football ball once exploded because it was on the sun for too long







)
Using water/methanol I can get K03S pushing 15 psi of air inside the engine at 40C / 5000rpm and I can certainly get GT35 pushing 15 psi of air nside the engine at 40C / 5000rpm.
Why is GT35 making more (read double) power?

Have you not read the thread?
First of all, lets lower the boost because a k03 cannot make 15psi at 5000rpm. Lets say 10psi at 5000 rpm. Now assuming air temp is the same with a k03 at 10psi, and a 35r at 10psi. The k03 turbine housing is too small and will restrict the engine, that is one of the reasons why it will not make as much power. But if you think of it just as 10psi going in the engine at 40 degrees C, then it's not going to make a difference whether it's coming from a 35r or a k03...
"It pushes more air" is not an reason and that makes absolutely no sense.


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## iThread (Sep 27, 2005)

Careful folks, it's starting to get heated.


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## Agtronic (May 14, 2001)

*Re:*


_Quote, originally posted by *[email protected]* »_Nothing confusing about what he said. On the contrary, its overly simplified

It's not over simplified. He's trying to make people understand the simple point of this thread, which is that CFM is dictated by the motor. All the extra info in this thread has nothing to do with the point, and is just people trying to show off what they know about turbos, and beating around the bush. 

_Quote, originally posted by *[email protected]* »_Dont worry guys. I dont think the physics and characteristics in what each and every turbo offers isnt completely dictated by the engine. The turbos have something to contribute to this whole equation. You can see it in the boost curves, surge points, fluttering, bov and wastegate springs boost controller settings,etc etc, needed per application. Each turbo must be set up differently on the SAME engine. Some would say its due to the restriction of the engine, which plays a role until you see the disparity in the boost plots. What do you know? The turbo cfm which speeds up and increases density/time actually controls the boost/rpm plot! What a novel idea!

None of this has anything to do with what is trying to be made clear in this thread. This is overly complicating things, and would apply if we were discussing turbo systems as a whole, but we're not. We're trying to make people accept the very basic principle behind boost pressure and flow rate. Wastegate springs do not have anything to do with the discussion.
Not trying to bash anyone, but I think everyone is beating around the bush, and trying to show that they know a lot about turbo kits, instead of just accepting the basic laws of physics.

_Quote, originally posted by *The*Fall*Guy* »_I understood every word he said... he tryed separating everything and attempted to prove that nothing was related.. unless of course he said it. Then the correlation made all the sense in the world. Carefully re-read everything he said. he contradicted himself all over the place. He got hung up on the deffinition of a couple words, and used this as a reason to insult everyones intelligence... 

He hasn't contradicted himself in a single post in this entire thread. You guys are throwing out random analogies that do not apply to engines, changing words and theories around, and saying that he thinks a k03 makes the same power as a gt30. Which he never said.
You guys are not understanding the point of the discussion, and are stuck on trying to prove thom337 wrong, instead of trying to understand his point, which is still 100% correct.
If you measure 30 psi at the intake manifold, and an IAT of 68°F, on a given engine set to 5000 RPM, with the same turbine on the back of the engine, you will have the exact same air volume and air mass going into the engine, which would make the exact same amount of power, whether the compressor feeding this intake manifold was a K03 or a GT35R. This is what thom337 has been trying to get everyone to understand. This DOES NOT IMPLY that the both turbos are capable of the same power, because everyone agrees that the k03 compressor would NEVER been able to feed a clean, dense charge of air at these elevated flow rates. thom337 never said this would happen in the real world. 
The only thing we have been trying to clear, is that the larger turbo is NOT FLOWING MORE CFM into the motor, it is simply flowing a denser charge when the engine is at higher flow rates (RPM).


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## mescaline (Jul 15, 2005)

*Re: (BoostinBejan)*


_Quote, originally posted by *BoostinBejan* »_
Have you not read the thread?
First of all, lets lower the boost because a k03 cannot make 15psi at 5000rpm. Lets say 10psi at 5000 rpm. Now assuming air temp is the same with a k03 at 10psi, and a 35r at 10psi. The k03 turbine housing is too small and will restrict the engine, that is one of the reasons why it will not make as much power. But if you think of it just as 10psi going in the engine at 40 degrees C, then it's not going to make a difference whether it's coming from a 35r or a k03...
"It pushes more air" is not an reason and that makes absolutely no sense.

turbine housing is too small and will restrict the engine? You're trying to escape an explanation, WHY is 35r making double the power that k03s is making at same psi and same intake temperatures? Because turbine housing is too small? Wanna break this down for me please, start from a single combustion process and why is turbine hosuing such a restriction.
All I see here is yada yada, turbo efficiency, IATs, boost... but no one is actually saying anything.


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## mescaline (Jul 15, 2005)

*Re: Re: (Agtronic)*


_Quote, originally posted by *Agtronic* »_
If you measure 30 psi at the intake manifold, and an IAT of 68°F, on a given engine set to 5000 RPM, with the same turbine on the back of the engine, you will have the exact same air volume and air mass going into the engine, which would make the exact same amount of power, whether the compressor feeding this intake manifold was a K03 or a GT35R. This is what thom337 has been trying to get everyone to understand. This DOES NOT IMPLY that the both turbos are capable of the same power, because everyone agrees that the k03 compressor would NEVER been able to feed a clean, dense charge of air at these elevated flow rates. thom337 never said this would happen in the real world. 
The only thing we have been trying to clear, is that the larger turbo is NOT FLOWING MORE CFM into the motor, it is simply flowing a denser charge when the engine is at higher flow rates (RPM).

Air density is directly related to temperature and pressure, you can't say both turbos are flowing same air mass and same volume and then say but bigger turbo makes more power...WHY is it making more power then?


_Modified by mescaline at 10:46 AM 8-30-2009_


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## Agtronic (May 14, 2001)

_Quote, originally posted by *mescaline* »_turbine housing is too small and will restrict the engine? You're trying to escape an explanation, WHY is 35r making double the power that k03s is making at same psi and same intake temperatures? Because turbine housing is too small? Wanna break this down for me please, start from a single combustion process and why is turbine hosuing such a restriction.

If you were able to get the charge from the K03 down to the same temp as the charge from the GT35R, the only reason the 35R would make more power is because of the increase in volumetric efficiency caused by the less restrictive turbine.
Same reason a 50 trim will make more power with a tubular manifold than with a cast iron log manifold, at the exact same boost level.

_Quote, originally posted by *mescaline* »_
Air density is directly related to temperature and pressure, you can't say both turbos are flowing same air mass and same volume and then say but bigger turbo makes more power...WHY is it making more power then?

I never said the larger turbo would make more power at the same mass flow, I said :

_Quote, originally posted by *Agtronic* »_If you measure 30 psi at the intake manifold, and an IAT of 68°F, on a given engine set to 5000 RPM, with the same turbine on the back of the engine, you will have the exact same air volume and air mass going into the engine, which would make the exact same amount of power, whether the compressor feeding this intake manifold was a K03 or a GT35R.

NOW, in the real world, the ONLY 2 REASONS a larger turbo makes more power, and as I said on the first page of this thread, is because :
1) Larger turbos have larger compressors that are more efficient at higher flow rates. (They are capable of feeding cool, dense air at higher flow rates).
2) Larger turbos have larger turbines that help the engine breathe in more volume.
It's really that simple.


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## mescaline (Jul 15, 2005)

*Re: (Agtronic)*


_Quote, originally posted by *Agtronic* »_
If you were able to get the charge from the K03 down to the same temp as the charge from the GT35R, the only reason the 35R would make more power is because of the increase in volumetric efficiency caused by the less restrictive turbine.
Same reason a 50 trim will make more power with a tubular manifold than with a cast iron log manifold, at the exact same boost level.
I never said the larger turbo would make more power at the same mass flow, I said :
NOW, in the real world, the ONLY 2 REASONS a larger turbo makes more power, and as I said on the first page of this thread, is because :
1) Larger turbos have larger compressors that are more efficient at higher flow rates. (They are capable of feeding cool, dense air at higher flow rates).
2) Larger turbos have larger turbines that help the engine breathe in more volume.
It's really that simple.

Again you didn't answer my question, we have intercoolers to take care of air density, air at [email protected] psi have same density on matter what turbocharger is pushing it.
How is larger turbines helping breathe in more volume? You said that volume is constant with whatever turbo you slap on. You said this on first page, now you're contradicting yourself.
We have two situations as far as charging goes, we have K03S pushing 10 psi at 50C temperature air and we have 35R pushing 10 psi at 50C, air density is the same because intercooler is taking care of extra heat that K03S is making (even tho i think k03s at 10 psi is pretty efficient). 
Read my example about balloon and the fridge on previous page








I want to believe thom but his theory is not answering my questions, I want somebody that really KNOWS to break this down for me but it seems everyone is just throwing words like turbo efficiency and crap like that without REAL explanation.
Could it be that less restrictive turbine is allowing all of exhaust gases to escape chamber and allowing more air to enter into cylinders? If yes then this automatically makes you wrong because in that case more air volume will actually enter the cylinder because of more space, no burned gases present








pick your destiny


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## animaniac (May 26, 2005)

*Re: (Agtronic)*


_Quote, originally posted by *Agtronic* »_
If you were able to get the charge from the K03 down to the same temp as the charge from the GT35R, the only reason the 35R would make more power is because of the increase in volumetric efficiency caused by the less restrictive turbine.
Same reason a 50 trim will make more power with a tubular manifold than with a cast iron log manifold, at the exact same boost level.
I never said the larger turbo would make more power at the same mass flow, I said :
NOW, in the real world, the ONLY 2 REASONS a larger turbo makes more power, and as I said on the first page of this thread, is because :
1) Larger turbos have larger compressors that are more efficient at higher flow rates. (They are capable of feeding cool, dense air at higher flow rates).
2) Larger turbos have larger turbines that help the engine breathe in more volume.
It's really that simple.

Larger turbos have bigger turbine housings which makes it easier for the piston to expel in the exahust stroke, this means on a smaller turbo with a small turbine housing you get quick spool up time but because the housing is small the piston doesnt push out all of the combusted gasses, so when the intake valve opens the chamber still has some of the burned gasses in their.
On a bigger turbine housing the piston is able to expel possibly all of the combustion gasses and on the intake stroke is able to to fit more air in the chanber due to ve volumetric efficiency.
Hense why bigger turbos using same psi as small turbos make more bhp, but the downside is increased boost threshold and possibly lag due to the increase in turbine and compressor housings.
The only way around this is to run a variable turbine geometry turbo!


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## [email protected] (Oct 23, 2008)

*Re: Re: (Agtronic)*


_Quote, originally posted by *Agtronic* »_
It's not over simplified. He's trying to make people understand the simple point of this thread, which is that CFM is dictated by the motor. All the extra info in this thread has nothing to do with the point, and is just people trying to show off what they know about turbos, and beating around the bush. 
None of this has anything to do with what is trying to be made clear in this thread. This is overly complicating things, and would apply if we were discussing turbo systems as a whole, but we're not. We're trying to make people accept the very basic principle behind boost pressure and flow rate. Wastegate springs do not have anything to do with the discussion.
Not trying to bash anyone, but I think everyone is beating around the bush, and trying to show that they know a lot about turbo kits, instead of just accepting the basic laws of physics.
He hasn't contradicted himself in a single post in this entire thread. You guys are throwing out random analogies that do not apply to engines, changing words and theories around, and saying that he thinks a k03 makes the same power as a gt30. Which he never said.
You guys are not understanding the point of the discussion, and are stuck on trying to prove thom337 wrong, instead of trying to understand his point, which is still 100% correct.
If you measure 30 psi at the intake manifold, and an IAT of 68°F, on a given engine set to 5000 RPM, with the same turbine on the back of the engine, you will have the exact same air volume and air mass going into the engine, which would make the exact same amount of power, whether the compressor feeding this intake manifold was a K03 or a GT35R. This is what thom337 has been trying to get everyone to understand. This DOES NOT IMPLY that the both turbos are capable of the same power, because everyone agrees that the k03 compressor would NEVER been able to feed a clean, dense charge of air at these elevated flow rates. thom337 never said this would happen in the real world. 
The only thing we have been trying to clear, is that the larger turbo is NOT FLOWING MORE CFM into the motor, it is simply flowing a denser charge when the engine is at higher flow rates (RPM).

Well, I dont buy that. Its like saying a ball rolls down the hill. Without accounting for hill angle, headwind, bumps in the road, etc.
Do you see me talking about power? Mincing words? I'm bringing on other aspects of turbocharging theory that may offset alot of the things that are being said.
BTW, i thought the point of this topic is turbo theory and not engine VE's.. I suggest you go to the NA forums..
You base statement about tubulars over logs is indicative of your oversimplification. I can show you areas where the tubular will not make as much as the cast log.
Again, we are all (maybe i'm generalizing here) aware of what is being said. And I'm not refuting that. But your larger turbo not flowing more air at a certain condition is just not a very useful piece of information. There is no application for it. Its just a math equation under a certain condition. Who cares??



_Modified by [email protected] at 2:40 PM 8-30-2009_


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## The*Fall*Guy (Aug 10, 2009)

*Re: Re: ([email protected])*

My point exactly... Thanx for summing it up Arnold...


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## animaniac (May 26, 2005)

*Re: Re: (The*Fall*Guy)*

Overall the turbo charger is an amasing device, without them we'd never have super fast cars which dont have big engines and dont have high petrol consumption, and we'd never be able to break the power to weight ratio barrier.
Although the Japanese have tried tuning 2.0l engines to gain high bhp figures with some sucess, but there is no alternative to a smallish engine with a big turbo on it.
After driving a turbo charged vehicle it would be hard for me not to have a turbo charged car and not be able to have that sudden increase in acceleration which can save your life in overtaking and pulling off situations, not unless i was in some supercar of course.
But if i was buying a super car it would probably be turbocharged because when crusing off boost why the hell should it use slightly less petrol than when full throttling!
If it wasnt for alfred buchi this topic wouldnt exist and neither would any of the T forums, we'd be stuck with the supercharger which acts as an engine parasite together with it's high rebuilding costs in which case it's cheaper to buy a new car!


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## killa (Nov 26, 2000)

bah, why are we still on this?
1) large compressor = less compressor speed to achieve the same psi = cooler charge
2) Larger compressor needs a larger turbine to keep it from surging and and to keep up with the exhaust gases thus keeping VE up
3) Here's one that i meant to throw on here, larger turbos in general running the same psi *should* make the same amount of *torque* but *more HP* since you're making the same torque at a later rpm all things being equal.
but you still can't fit more air in the motor at the same psi


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## killa (Nov 26, 2000)

*Re: (Agtronic)*


_Quote, originally posted by *Agtronic* »_
NOW, in the real world, the ONLY 2 REASONS a larger turbo makes more power, and as I said on the first page of this thread, is because :
1) Larger turbos have larger compressors that are more efficient at higher flow rates. (They are capable of feeding cool, dense air at higher flow rates).
2) Larger turbos have larger turbines that help the engine breathe in more volume.
It's really that simple.

I'd throw in there that the power (torque) comes later in the rpm band which translates into more hp and i'd say we have it all covered







http://****************.com/smile/emthup.gif


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## joedubs (Feb 2, 2004)

*Re: (killa)*

i only read up to page 5 or so... but I was looking through the maestro thread and i just can't bite my tongue anymore.
People need to realize the difference between volume and mass.
It seems like everybody is stuck on the "a large turbo flows more volume than small turbo therefore it makes more power" argument, while he opposite side is "an engine only accepts volume x therefore both turbo's flow the same volume".
By saying "a ko3s can flow x volume" and "a gt35r can flow 2x volume" means absolutely nothing.... this essentially just tells you that the gt30 COULD flow double the volume. the engine will still only ACCEPT the same volume of air at any given time.
THE DIFFERENCE IN THE VOLUME means that that turbo could potentially produce that much more *pressure*.... pressure is caused when you take a LAGER "volume" of air and COMPRESS it to take up a smaller space.
I don't know the equations and mathematics to explain it... but a k03s will not flow the volume of air to create 2bar of positive pressure in our engines at 5krpm. people just need to face it.... the power increase from turbo A to B is due to the cooler/more dense air.
mass is a measurement of *how much*.
volume is a measurement of *how much space*.
i'm sorry if its been addressed... i just needed to get it out.


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## [email protected] (Oct 23, 2008)

*Re: (joedubs)*

http://www.5min.com/Video/Volu...07432
A foray into some info pretty much supports some of the things that I've been saying albeit, unscientifically. I was never really sold on capping turbocharged apps at only 100% VE. There are ways to surpass this. VE's are needed to calculate mass flow. There are real world obstructions to obtaining higher levels of efficiency (manifold runner designs, valving, etc.) that are overcome somewhat by more efficient compressors. This is why theory is not very accurate at times, but just a base to work with.
I guess you can calculate mass flow w/o VE's (map sensor, maf signal w/ temp monitoring) to measure cylinder mass, but its really not very practical.


_Modified by [email protected] at 8:34 PM 8-31-2009_


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## dubchuck117 (Feb 6, 2009)

heres an example my buddy has a mustang with a 60mm holset turbo, intercooler, and what not at 9psi. if he put a k03 on and didnt change a thing i have a hard time believing hed be making 411hp and 460tq to the wheels still


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## BoostinBejan (Apr 13, 2009)

*Re: (dubchuck117)*


_Quote, originally posted by *dubchuck117* »_heres an example my buddy has a mustang with a 60mm holset turbo, intercooler, and what not at 9psi. if he put a k03 on and didnt change a thing i have a hard time believing hed be making 411hp and 460tq to the wheels still

oh yeah that's a great example, you have a hard time believe it, so it might be false...


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## DK_GTI_racer (Oct 4, 2007)

*Re: (BoostinBejan)*

yahoo according to the info in this thread, all i need to do is make my w/m spray directly in to the turbo inlet and then their is no problem making up to 500hp or more on my GT28rs, great


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## BoostinBejan (Apr 13, 2009)

*Re: (DK_GTI_racer)*


_Quote, originally posted by *DK_GTI_racer* »_yahoo according to the info in this thread, all i need to do is make my w/m spray directly in to the turbo inlet and then their is no problem making up to 500hp or more on my GT28rs, great









No, that is clearly not what is being said here. If you are too ignorant to ignore the thread and randomly post, please do not post at all becuase it's not contributing. 
If your GT28rs could flow up top where the engine itself is effecient at lets say 7000rpm, sure it'd make good power. but it can't, because of the size.


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## killa (Nov 26, 2000)

*Re: (dubchuck117)*


_Quote, originally posted by *dubchuck117* »_heres an example my buddy has a mustang with a 60mm holset turbo, intercooler, and what not at 9psi. if he put a k03 on and didnt change a thing i have a hard time believing hed be making 411hp and 460tq to the wheels still

No because the turbine will choke, VE will decrease due to backpressure from the k03 turbine wheel and the compressor simple can't flow enough to fill the mustang's engine at 9 psi. You wouldn't even be able to plot the mustang motor in a k03 map as it would fall way to the right of the compressor map ( X axis in the map) and it wouldnt have enough flow for the pressure to reach 9 ( Y axis).


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## dubchuck117 (Feb 6, 2009)

*Re: (killa)*


_Quote, originally posted by *killa* »_
No because the turbine will choke, VE will decrease due to backpressure from the k03 turbine wheel and the compressor simple can't flow enough to fill the mustang's engine at 9 psi. You wouldn't even be able to plot the mustang motor in a k03 map as it would fall way to the right of the compressor map ( X axis in the map) and it wouldnt have enough flow for the pressure to reach 9 ( Y axis).

so in laymans terms, no because it wouldnt flow enough air?


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## killa (Nov 26, 2000)

*Re: (dubchuck117)*


_Quote, originally posted by *dubchuck117* »_
so in laymans terms, no because it wouldnt flow enough air?

for that specific application? yes, but that was never the origial questions as the OP stated the same motor and same rpm. But yes, the k03 can't flow enough for that specific motor and this case is both about CFM and PSI which would represent the X and Y axis on the compressor map.
Again, this is not what the OP was arguing so i have to agree with Thom


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## dubchuck117 (Feb 6, 2009)

*Re: (killa)*


_Quote, originally posted by *killa* »_
for that specific application? yes, but that was never the origial questions as the OP stated the same motor and same rpm. But yes, the k03 can't flow enough for that specific motor and this case is both about CFM and PSI which would represent the X and Y axis on the compressor map.
Again, this is not what the OP was arguing so i have to agree with Thom 

thom337 clearly stated that cfm had no impact on turbo performance on *multiple* occasions and this is undeniable evidence hes just wrong. i understand where hes coming from but theory and practice are two completly different things. when people start to overanalyze things facts get twisted (sometimes beyound reason)


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## BoostinBejan (Apr 13, 2009)

*Re: (dubchuck117)*


_Quote, originally posted by *dubchuck117* »_
thom337 clearly stated that cfm had no impact on turbo performance on *multiple* occasions and this is undeniable evidence hes just wrong. i understand where hes coming from but theory and practice are two completly different things. when people start to overanalyze things facts get twisted (sometimes beyound reason)

You really need to read or understand what he was talking about and not just take parts from it. This is how stupid arguments start.
When one says "oh this turbo flows this many CFM, and this one only flows this many" is when it starts to get stupid. At a certain rpm, temp, boost, etc it doesn't matter what turbo you have, the same amount of air will get into the engine no matter what the turbo can produce as far as CFM's (assuming it's at a low enough rpm that both turbos can produce the same boost)


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## The*Fall*Guy (Aug 10, 2009)

*Re: (BoostinBejan)*

CFM does matter.. Using the hypothetical Ford 302 vs 1.8T as an example. It takes a lot more CFM to overcome what a 302 ingests in naturally aspirated form to achieve that hypothetical 9 psi of boost pressure than it does in a 1.8T. Same can be said with a modified 1.8T equipped with an AEB head, larger intake mani, increased displacement, cat cams, etc. It will most certainly require more CFM's to achieve the desired boost level on the better flowing setup. Because the intake tract and cylinders have been "opened up" requiring more CFM to bring said setup to the desired boost level..


_Modified by The*Fall*Guy at 4:23 PM 9-1-2009_


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## killa (Nov 26, 2000)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_CFM does matter.. Using the hypothetical Ford 302 vs 1.8T as an example. It takes a lot more CFM to overcome what a 302 ingests in naturally aspirated form to achieve that hypothetical 9 psi of boost pressure than it does in a 1.8T. Same can be said with a modified 1.8T equipped with an AEB head, larger intake mani, increased displacement, cat cams, etc. It will most certainly require more CFM's to achieve the desired boost level on the better flowing setup. Because the intake tract and cylinders have been "opened up" requiring more CFM to bring said setup to the desired boost level..

_Modified by The*Fall*Guy at 4:23 PM 9-1-2009_

But that wasn't his argument, we can drag this on and on and even throw more variables into it. The motor has to be kept constant so either a Ford 302 or a vw 109 not one vs the other. So we have the same motor, same pressure and rsame rpm, the bigger turbo will make more power due to higher compressor efficiency because of less shaft speed and larger turbine that gets rid of more exhaust flow thus keeping VE up. A good example would be that of a T3 Super 60 needs roughly 115,000 rpm to generate 1 bar whereas a T61 needs roughly 74,000 rpm.
And last but not least the Torque generated by the larger turbo will be at a later rpm which equals more hp at the same torque level so a T3 making 300wtq and a 35R making the same amount of torque will have different hp readings since the 35R will make it at a higher rpm. http://****************.com/smile/emthup.gif


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## The*Fall*Guy (Aug 10, 2009)

*Re: (killa)*

I used the 302 as my first example. My second example was a "massaged" 1.8T. 
It was a simple example of how CFM matters. And yes it is totally relevant to the discussion. thom337 and agtronic have made a point of attempting to own this thread with their main argument being that CFM doesn't matter. It does matter in so many ways its not even funny. A turbo capable of flowing more CFM at a given rpm is also more efficient by default. It will supply a given boost pressure at a lower temperature due to its inheritant ability to flow more CFM. It will remain in its efficiency range longer and provide higher boost with less heat soak by remaining efficient longer than a turbo that flows less CFM.


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## ncsumecheng (Nov 1, 2005)

*Re: (The*Fall*Guy)*

Ok, let me apply a fluid pump perspective:
-Head * density * g = Pressure (the Y axis)
-Flow (the X axis)
The pump curve:








Notice that different pumps generate different curves on the graph. Note that if you pick an identical pressure of two pumps, you get different flow rates. 
This CLEARLY demonstrates that if a K03s is the lower curve on the graph, and the 35R is the higher, if you draw a line at a constant pressure, the larger pump flows more.
Here is a "pump" curve of a 30R:








Turbocharger "maps" display multiple "pump" "RPM's", if speaking in terms of fluids. 
Now, the why about displacement in a motor vs boost pressure.
Here:








As displacement in the denominator increases, MAPreq decreases.
For heaven's sake, people talk about this stuff that have never taken a test on it they had to pass to be able to put food on the table at home.


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## NOLA_VDubber (May 24, 2007)

*Re: (The*Fall*Guy)*

edit: got beat by ncsumecheng!!!

_Quote, originally posted by *The*Fall*Guy* »_I used the 302 as my first example. My second example was a "massaged" 1.8T. 
It was a simple example of how CFM matters. And yes it is totally relevant to the discussion. thom337 and agtronic have made a point of attempting to own this thread with their main argument being that CFM doesn't matter. It does matter in so many ways its not even funny. A turbo capable of flowing more CFM at a given rpm is also more efficient by default. It will supply a given boost pressure at a lower temperature due to its inheritant ability to flow more CFM. It will remain in its efficiency range longer and provide higher boost with less heat soak by remaining efficient longer than a turbo that flows less CFM.

You are using incompressible pipe flow theory to defend your position; this is totally inapplicable since the volumetric flow rate through the engine is determined by the engine and not the turbo connected to it.
In pipe flow, say a pump pushing water through a pipe for example, the volumetric flow rate is defined by the pump for some given pressure. A big pump operating such that there's a 20psi jump across it will flow much more volume than a small pump seeing the same pressure differential. While great for exhaust sizing, these principles do not apply to this discussion because
a) we are dealing with compressible flow now
b) more importantly, the volumetric flow of the system is* FIXED* by displacement and rpm
Lets take a 1 cylinder, 2 cycle engine with a displacement of 1 cubic foot. Since it ingests its volume once every revolution, at 1000rpm this engine ingests 1000cfm. No mater how big of a turbo you use to blow more air into the engine, there will still only be 1000cf of VOLUME flowing through the intake mani at 1000rpm. Note, however, that the turbo'd engine will be flowing more MASS through, and that at the inlet of the turbo there will be much more than 1000cfm entering.
This is where the problems are arising. You guys need to take a minute to learn the difference between volumetric flow rate and mass flow rate. Forget about power, forget about, VE's, forget about the turbine altogether. Thom's argument is simply that the VOLUMETRIC flow rate through an engine (boosted or not, big turbo or little turbo) is determined by the engine size and speed only. No matter what snail you stick on there, they are all going to "flow" the same. 
*The only difference (the only one that matters for this discussion) between compressors is that some can produce this prescribed flow rate at higher pressures than others.*
I was going to take the time to put together a nice set of drawings and equations explaining the concepts, but i just don't feel like it. Instead, may i recommend you guys read the following section taken from here:

_Quote, originally posted by *http://www.automotivearticles.com/Turbo_Selection.shtml* »_









If you look at the equations above, you'll see that no where in the equation for engine volumetric flow rate (EVF) does the compressor size come in to play. Second, notice that in the equation for engine mass flow rate, the compressor size has nothing to do with it.
This is it. This is all thom was trying to say. nothing more. of course the turbine plays a role in how much power you will make at some pressure. of course compressor size effects where you will see this power and how much torque you can see. However, these things were never in question. The only thing this man has been saying all along is that turbo size has nothing to do with the VOLUMETRIC flow rate of an engine and everything to do with the MASS flow rate!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
/rant

























_Modified by NOLA_VDubber at 9:21 PM 9-1-2009_


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## [email protected] (Oct 23, 2008)

*Re: (NOLA_VDubber)*

That excerpt is obviously AFTER understanding Comp Flow charts. Come on man... One doesnt go without the other... No one is trying to diffuse the importance of mass flow...
Anyways, the fact that you think a compressor cannot surpass an engine's volumetric efficiency is bunk. If VE is raised to 120%, a 100cc cylinder will emit 120cc's in volume... believe it..
Four years ago i plotted several charts that represents how things would look APPROXIMATELY if used on a 1.8t engine
























All this data is correct, but I wouldnt hang my hat on just data and assume that what i did on paper would happen on the field..


_Modified by [email protected] at 7:39 PM 9-1-2009_


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## HSTuning (Jul 1, 2009)

*FV-QR*


_Quote, originally posted by *[email protected]* »_
Anyways, the fact that you think a compressor cannot surpass an engine's volumetric efficiency is bunk. If VE is raised to 120%, a 100cc cylinder will emit 120cc's in volume... believe it..


In what state and at what pressure? Sure if you've compressed a MASS of air into a 100cc cylinder at 30psi and it comes out of said cylinder at 15psi it will expand and fill up a larger volume.
One of the things I'm not sure if it was covered is, these "flow" rates of said turbos are based on rate, not on volume/mass alone. Sure a ko3s can flow 52lb of air, but how long does it take it to do that? If a 35R flows 52lb/min, in 60sec it is capable of flowing 52lb of air. Now, at atmospheric pressure 52lb is going to be a pretty large volume. At 30psi, maybe just maybe you are able to fit every bit of that 52lb into your 1.8T, charge piping, intercooler, etc. I know there are conversions for cfm to lb/min but 1 cubic foot is 1 cubic foot. It doesn't matter if it's 1psi or 30psi. There's still just one cubic foot of air there (volumetrically speaking). Now at 30psi that 1 cfm will definitely weigh more, and thus have more mass. Everyone's (generally) assuming the density of the air stays the same...which is a measure of mass over volume.
So you have your same engine, and forgetting the turbo's compressor cover, the rest of your system remains identical. Your volume is the same, period. The ko3s you just removed is going to fill up the volume just fine, so is a 35R. But then at x rpm you get to the point where the ko3's max lb/min "flow" rate is exceeded by a 35R's max lb/min "flow" rate. The 35R is still filling up the same volume but b/c of the identical restriction of the motor that the ko3s had, it's cramming the air up into the same place. Note NOLA's explanation of compressible flow vs. imcompressible flow.
So yes and no I guess. Yea, 35R can flow more volume of air than a ko3s. Will it on the same motor? No. Under pressure the volume stays the same, the mass rate increases, thus the need for more fuel.


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## The*Fall*Guy (Aug 10, 2009)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_I used the 302 as my first example. My second example was a "massaged" 1.8T. 
It was a simple example of how CFM matters. And yes it is totally relevant to the discussion. thom337 and agtronic have made a point of attempting to own this thread with their main argument being that CFM doesn't matter. It does matter in so many ways its not even funny. A turbo capable of flowing more CFM at a given rpm is also more efficient by default. It will supply a given boost pressure at a lower temperature due to its inheritant ability to flow more CFM. It will remain in its efficiency range longer and provide higher boost with less heat soak by remaining efficient longer than a turbo that flows less CFM.
 Re -read it.... There is not one thing that I stated above that is false.. CFM matters.. Period.. I'm not arguing against any of the points made except for the one that thom337 hammered home about fifty times. That CFM doesn't matter.. It does.. I understand that it was more of a play on words. But he never admitted this..
I understand what Mass Flow is.. It is the collective density, and CFM that is being flowed by the compressor.. Determined by the charge temp, cfm, relative humidity, etc., of the air being flowed by the compressor housing of the turbo.. There are also many other factors that determine the Mass flow, right on down to the exact chemical makeup of the air being moved by the compressor housing... What's my point?? More than half of "mass flow" is determined by the cfm that the compressor can move efficiently. The rest is determined by temperature, etc. Of course this "temperature" of the air being flowed is directly related to how efficiently the compressor can move whatever volume or CFM.. To say that CFM isn't important is simply ignoring how all of these factors are related...


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## HSTuning (Jul 1, 2009)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_To say that CFM isn't important is simply ignoring how all of these factors are related... 


Except that CFM is a measure of what a turbo is capable of flowing in an open environment. In one minute a 35R will suck in and spit out more air than a ko3s will in one minute. But in a restricted system, the CFM remains absolutely positively identical. If you filled your ic piping, motor, core, everything that air goes through with water, drained it and measured it, and converted to cubic feet, that is exactly how much volume of air is moving through the system at any given point no matter if it's a 35R or ko3s. since we can't compress water (in this application) that doesn't tell you the mass inside this controlled volume.


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## NOLA_VDubber (May 24, 2007)

*Re: ([email protected])*

I was under the impression these guys were purely arguing compressor performance, all other things remaining constant. You must forgive me if the argument has changed...the thread is 7 pages long now








Anyway, its clear to see how VE effects mass and volumetric flow rate by reading the first line of that last paragraph:

_Quote, originally posted by »_Finally, multiply N by the volumetric efficiency of your engine (VE)

If changing to a larger compressor means you must step up to a larger turbine and change the VE of the engine, then it is seen that the volumetric flow will increase for some given charge pressure at some given rpm.


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## thom337 (Oct 13, 2007)

*Re: (NOLA_VDubber)*

Glad that this has become a "technical" discussion again, even if everyone doesn't agree. http://****************.com/smile/emthup.gif


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## NOLA_VDubber (May 24, 2007)

*Re: (The*Fall*Guy)*


_Quote, originally posted by *The*Fall*Guy* »_ To say that CFM isn't important is simply ignoring how all of these factors are related... 


EDIT: thom's here now so i'll let him speak for himself










_Modified by NOLA_VDubber at 10:30 PM 9-1-2009_


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## [email protected] (Oct 23, 2008)

*Re: FV-QR ([email protected])*


_Quote, originally posted by *[email protected]* »_
In what state and at what pressure? Sure if you've compressed a MASS of air into a 100cc cylinder at 30psi and it comes out of said cylinder at 15psi it will expand and fill up a larger volume.


Yes and arent we talking about COMPRESSing air here? If its going in charged, its coming out charged. Arbitrary number that isnt too far off w/ a medium sized turbo...
150% [email protected] 2.0L engine at sea level

_Quote »_
One of the things I'm not sure if it was covered is, these "flow" rates of said turbos are based on rate, not on volume/mass alone. Sure a ko3s can flow 52lb of air, but how long does it take it to do that? If a 35R flows 52lb/min, in 60sec it is capable of flowing 52lb of air. Now, at atmospheric pressure 52lb is going to be a pretty large volume. At 30psi, maybe just maybe you are able to fit every bit of that 52lb into your 1.8T, charge piping, intercooler, etc. I know there are conversions for cfm to lb/min but 1 cubic foot is 1 cubic foot. It doesn't matter if it's 1psi or 30psi. There's still just one cubic foot of air there (volumetrically speaking). Now at 30psi that 1 cfm will definitely weigh more, and thus have more mass. Everyone's (generally) assuming the density of the air stays the same...which is a measure of mass over volume.
So you have your same engine, and forgetting the turbo's compressor cover, the rest of your system remains identical. Your volume is the same, period. The ko3s you just removed is going to fill up the volume just fine, so is a 35R. But then at x rpm you get to the point where the ko3's max lb/min "flow" rate is exceeded by a 35R's max lb/min "flow" rate. The 35R is still filling up the same volume but b/c of the identical restriction of the motor that the ko3s had, it's cramming the air up into the same place. Note NOLA's explanation of compressible flow vs. imcompressible flow.
So yes and no I guess. Yea, 35R can flow more volume of air than a ko3s. Will it on the same motor? No. Under pressure the volume stays the same, the mass rate increases, thus the need for more fuel


No argument there... BTW, you guys have much to much time on your hands. With all this number crunching (me included but not publicly), you would think there would be some pretty mean cars out of these guys...


_Modified by [email protected] at 8:43 PM 9-1-2009_


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## HSTuning (Jul 1, 2009)

*Re: FV-QR ([email protected])*


_Quote, originally posted by *[email protected]* »_
Yes and arent we talking about COMPRESSing air here? If its going in charged, its coming out charged. Arbitrary number that isnt too far off w/ a medium sized turbo...
150% [email protected] 2.0L engine at sea level

We are, some people may not be, but the way you said it, filling a 100cc cylinder with 120cc of air isn't going to make it 120cc of air inside a 100cc cylinder. It's 100cc of air at a higher pressure/density than if 100cc of air entered. Atleast that's how I read what you said...


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## [email protected] (Oct 23, 2008)

*Re: FV-QR ([email protected])*


_Quote, originally posted by *[email protected]* »_
We are, some people may not be, but the way you said it, filling a 100cc cylinder with 120cc of air isn't going to make it 120cc of air inside a 100cc cylinder. It's 100cc of air at a higher pressure/density than if 100cc of air entered. Atleast that's how I read what you said...

That would just be talking about the area in the container rather then what flows into and out of it... if that were the case in its absolution, how does the piston travel to tdc from its btdc state? It compresses it! Whoa! But it comes in already compressed as well, unlike an NA motor


_Modified by [email protected] at 9:01 PM 9-1-2009_


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## NOLA_VDubber (May 24, 2007)

*Re: FV-QR ([email protected])*


_Quote, originally posted by *[email protected]* »_
No argument there... BTW, you guys have much to much time on your hands. With all this number crunching (me included but not publicly), you would think there would be some pretty mean cars out of these guys...


if you only knew how much work i don't get done because of this forum...damn you vortex!!!!
one more post to make 8 pages of turbo fury


_Modified by NOLA_VDubber at 10:53 PM 9-1-2009_


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## HSTuning (Jul 1, 2009)

*Re: FV-QR ([email protected])*


_Quote, originally posted by *[email protected]* »_
That would just be talking about the area in the container rather then what flows into and out of it... if that were the case in its absolution, how does the piston travel to tdc from its btdc state?

Skip the "out of" portion for a sec. Without getting into engine dynamics, when the exhaust valves close and the intake valves open, the piston drops and the acceptable volume of air becomes what is inbetween the comp wheel and the top of the piston. At the point the intake valve closes the discussion ends. You have 100cc of air contained within the cylinder(before the piston rises), but how many lbs of air is it? It all depends on what the compressor wheel was able to push into the cylinder in the time the piston dropped. Once we get our air/fuel in there (the air part is what i thought this discussion was about), it becomes a new discussion which I don't think anyone is arguing. Right?


_Modified by [email protected] at 11:54 PM 9-1-2009_


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## NOLA_VDubber (May 24, 2007)

*Re: FV-QR ([email protected])*

^you must not forget about air left over in the chamber due to high exhaust back pressure, and you must not forget about the added benefits of pressure pulse waves resonating in the manifold/runner area. These things, and many more i'm sure, all effect how much air the engine is actually ingesting with respect to is total volume


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## HSTuning (Jul 1, 2009)

*Re: FV-QR (NOLA_VDubber)*

True, and this is just "engineering" talk where we choose to neglect these minor details. Real world it's not gonna be 100cc but just for argument sake, I think the 35R vs. ko3s "is it volume" debate is covered...


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## [email protected] (Oct 23, 2008)

*Re: FV-QR ([email protected])*


_Quote, originally posted by *[email protected]* »_
Skip the "out of" portion for a sec. Without getting into engine dynamics, when the exhaust valves close and the intake valves open, the piston drops and the acceptable volume of air becomes what is inbetween the comp wheel and the top of the piston. At the point the intake valve closes the discussion ends. You have 100cc of air contained within the cylinder(before the piston rises), but how many lbs of air is it? It all depends on what the compressor wheel was able to push into the cylinder in the time the piston dropped. Once we get our air/fuel in there (the air part is what i thought this discussion was about), it becomes a new discussion which I don't think anyone is arguing. Right?

_Modified by [email protected] at 11:54 PM 9-1-2009_

You're touching on why comp volume/flow matters now


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## thom337 (Oct 13, 2007)

*Re: (NOLA_VDubber)*

Just a brief blurb on VE, as it has become a topic of discussion.
The filling of a cylinder with VE is basically saying "how much of the displacement volume (V_d) is filled with air in comparison to the volume of air which is equal to the displacement volume". So, if the total volume is filled, you are at 100%. This is not a description of the number air molecules in the cylinder, it is a description of the state of a 3 dimensional space. So, how do we increase mass air in the cylinder if it is going to be fully filled by either a small turbo or a large turbo? Increase in cylinder DENSITY.
Now, it can get slightly more complicated. On a turbo car, the pressure in the exhaust manifold is almost always higher than the pressure in the intake manifold, often by more than a 2:1 margin. Fluids move from a balance in net pressure. So, during valve overlap events, there can be a considerable amount of exhaust being pushed back into the cylinder. This can result in the VOLUME of air in the cylinder being a part of a total volume, part of which is composed of exhaust gasses. This causes a DROP in volumetric efficiency. Can you still have more MASS air in this condition where air is only part of total volume than would be in the displacement volume at atmospheric conditions? Absolutely. If part of the cylinder is occupied by exhaust, can you have 100% VE? No. (a slight exception is below, but I think this is beyond the scope of this discussion) The key: again, density. 

Slightly more complicated, don't read this if you are already confused. (getting into turbine/ exhaust effects, not the original intent of my post) If there is no exhaust pressure pushing backflow into the engine / the intake pressure is sufficiently higher than the exhaust pressure, you can fill both the displacement volume (V_d), AND the clearance space in the combustion chamber (V_c). This is the only case in which I think it is appropriate to refer to volumetric efficiencies in excess of 100%. A better way to express this this would be to add another term to the volumetric flow equation posted earlier in the thread.
Again, because of the high ratio of exhaust pressure to intake pressure, you are basically guaranteed that you will never fill the full volume of both V_d and V_c. For a 1.8L engine with a 9.5:1 CR (just an example), you could theoretically achieve 112% VE. However, unless you have no exhaust presence in the cylinder, you will not achieve this value. The only exception to the CFM rule I was talking about earlier where two turbos at the same RPM must operate at the same cfm, is where a free-er flowing turbine or a compressor at a higher pressure which is better able to fill the cylinder due to a higher operating pressure has less pressure/backflow in the cylinder and allows the cylinder to have a greater volume ratio of air. But we are generally talking about a change in VE from 95%-105%, which certainly does not account for all of the power gains from a larger compressor. Its still very much about density AT a cfm. Again, this is getting into the exhaust side....the point of my original post was regarding compressors and the idea that CFM is engine controlled, and we must make the most of that by using pressure and temperature to increase density.
All this being said, the cfm of the turbo is still limited by the volumetric flow of the engine, which is determined by speed, displacement, and VE as stated in my first post. The main performance factor is still mass flow, and the way to achieve this is to increase density at the volume flow the engine is operating at.


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## HSTuning (Jul 1, 2009)

*Re: FV-QR ([email protected])*

I know that if I have a turbo that has twice the cfm rating as another I'm going to get more air in the same system, not necessarily more volume tho. More mass yes b/c with the increased cfm rating comes a higher lb/min rating as well.


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## [email protected] (Oct 23, 2008)

*Re: FV-QR ([email protected])*

NO, volumetric efficiencies going over 100% are mostly from increased intake manifold pressures. Superchargers w/ header systems routinely achieve well over 150% VE's... BTW, not much overlap events on turbocharger cams... sorry


_Modified by [email protected] at 9:26 PM 9-1-2009_


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## thom337 (Oct 13, 2007)

*Re: FV-QR ([email protected])*


_Quote, originally posted by *[email protected]* »_NO, volumetric efficiencies going over 100% are mostly from increased intake manifold pressures. Superchargers w/ header systems routinely achieve well over 150% VE's... BTW, not much overlap events on turbocharger cams... sorry

_Modified by [email protected] at 9:24 PM 9-1-2009_


Again, you physically cannot fill more space than there is to fill. Like I said, it would make more sense to just add a new term to the equation for V_c, so that you aren't going above 100%. Volume is nothing more than a 3 dimensional space, if you have air in 100% of it, you have 100% VE. It has nothing to do with mass.

The upper extent of VE is most certainly to fill the total physicaly space, beyond that there is no more VOLUME filling. If you have filled the V_d and the V_c, there is no more space. If you want to get more MASS air in the cylinder, you increase the density. VE is comparing volume filled to total volume. If you have filled the total volume (and perhaps the V_c), how can you go above this? 
More manifold pressure is a means of increasing mass in the cylinder by increasing density.


_Modified by thom337 at 12:34 AM 9-2-2009_


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## [email protected] (Oct 23, 2008)

*Re: FV-QR (thom337)*

in this case its the measure of what comes in/out. If you are also talking 100% cylinder filling, you do realize at the upstroke on a 100% filled cylinder it reduced to like 5% of the area that it took up? So why dont you think charged gases that are obviously compressable be injected into an area essentially overfilling/filling it? Excuse the clumsy terminology, but I'm shot (lots of work today..)


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## thom337 (Oct 13, 2007)

*Re: FV-QR ([email protected])*


_Quote, originally posted by *[email protected]* »_in this case its the measure of what comes in/out. If you are also talking 100% cylinder filling, you do realize at the upstroke on a 100% filled cylinder it reduced to like 5% of the area that it took up? So why dont you think charged gases that are obviously compressable be injected into an area essentially overfilling/filling it? Excuse the clumsy terminology, but I'm shot (lots of work today..)

They are definitely filling it, but they are filling it at a greater density than atmosphere. Logically, the maximum VOLUME of air that can be put in any volume container is the maximum volume of the container itself (V_d or volume at BDC). 
I think to some degree our issue here is that we are defining VE differently. I think in some of the cases that have been talked about, VE is being defined as including the density term. ie comparing the mass of the total displacement volume of air at atmosphere to the mass of air in the cylinder. In this case I have no problem with it being far greater than 100%.


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## DK_GTI_racer (Oct 4, 2007)

*Re: (BoostinBejan)*


_Quote, originally posted by *BoostinBejan* »_
No, that is clearly not what is being said here. If you are too ignorant to ignore the thread and randomly post, please do not post at all becuase it's not contributing. 
If your GT28rs could flow up top where the engine itself is effecient at lets say 7000rpm, sure it'd make good power. but it can't, because of the size.

You, Thom and a few others are stating that each turbo flow the same, but its the air density that rocks the planet - well then spraying w/m directly in to the compressor inlet (cooling turbo and affecting the air density wastly) then according to you guys it should not be a problem making that kind of insane powers on that "small" turbo or a k03 for that matter, because the CFM of air a turbo flows is not important its the same....
Well here is the thing, a turbo flows compressed air, which means you affect the density of air and you can easy overfill an engine more then 100%(mass) since its compressed air, and thats why bigger turbos flow more compressed air and make more power, end of debate. clearly the basics of how compressed air acts is misunderstood....so instead of just riding the wrong train others ride jump on the right one.


_Modified by DK_GTI_racer at 1:42 AM 9-2-2009_


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## HSTuning (Jul 1, 2009)

*Re: (DK_GTI_racer)*

So oddly enough I wake up this morning and first thing that's on my mind is this turbo thread and I had a new idea/way of explaining this. Sticking with mostly what I said last night but speaking more on volume now.
Despite the "controlled" volume of a motor setup, a bigger turbo DOES flow more VOLUME of air than a smaller one. The why is obviously related to the size of the wheel. When you calculate roughly what a pump is capable of flowing impeller size and # of blades is used to determine the flow rate...which is precisely why an HTA turbo flows more than a standard GT turbo. There is more surface area on the comp wheel, so with each revolution it throws more air.
Now onto the how, since I don't feel like using MS Paint right now, picture below that from your turbo to the cylinders a straight line of space. Deducing all your pipe bends, intercooler channels, and runners in the intake manifold to one straight line, the ko3s system would look like this:
|__|__|__|__|__|__|__|__|__|__|__|
Where each " | " represents a square area of air. Remember the volume shown is controlled, and the ko3s packs each | into this volume. Now with a 35R, this would look more like this:
|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|
Same controlled volume after the turbo, but more of | these. Well if you have more single square areas in the same volume, how'd they get there? Well if you measured airflow right out of the turbo you'd see then that the VOLUME of air it moves is greater on the 35R than the ko3s. By compressing it into the same space, the MASS increases, so more fuel needed.
Therefore, the age old analogy of "sink vs bathtub faucets" holds true. Water pressure in the house remains constant, the ko3s is the sink, the 35r is the bathtub. However only thing that's different is you can't compress the amount of water flowed in one minute by the bathtub into the same volume that the sink flowed in one minute.
Make sense?










_Modified by [email protected] at 7:04 AM 9-2-2009_


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## ncsumecheng (Nov 1, 2005)

*Re:*

Thom dude........if you decrease IAT's by 50 degrees F, you're only gaining about 10% chp. 
Density of air at 20 psi and 200F is .142 lb/ft3 and at 20 psi and 70F is .177 lb/ft3. Or that would be a 25% gain in power. A very drastic drop in intake charge temps.
I ran my K03s at about 140 deg F IAT's. My 3076 runs at almost the identical IAT's at the same boost pressure. 
So Thom, where is this magical gain from temperature difference? 
http://www.engineeringtoolbox.....html
This discussion is over.........
Buy this, I got an A in this class:








That book specifically addresses turbo and supercharging and their effects on the OTTO/Diesel cycles. It explicitly explains that when calculating these cycles for a turbo/supercharged engine, that VE is allowed to be calculated at greater than 100%. The amount that VE exceeds 100% is determined by the flow capacity of the turbo/supercharger as dictated by their pump curves.
Buy this:








This is a more practical application skipping the theory and uses laymans terms.
And lastly these two:
















If you want to speak on the same level I suggest those.


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## thom337 (Oct 13, 2007)

*Re: Re: (ncsumecheng)*


_Quote, originally posted by *ncsumecheng* »_Thom dude........if you decrease IAT's by 50 degrees F, you're only gaining about 10% chp. 
Density of air at 20 psi and 200F is .142 lb/ft3 and at 20 psi and 70F is .177 lb/ft3. Or that would be a 25% gain in power. A very drastic drop in intake charge temps.
I ran my K03s at about 140 deg F IAT's. My 3076 runs at almost the identical IAT's at the same boost pressure. 
So Thom, where is this magical gain from temperature difference? 
This discussion is over.........

That book specifically addresses turbo and supercharging and their effects on the OTTO/Diesel cycles. It explicitly explains that when calculating these cycles for a turbo/supercharged engine, that VE is allowed to be calculated at greater than 100%. The amount that VE exceeds 100% is determined by the flow capacity of the turbo/supercharger as dictated by their pump curves.
This is a more practical application skipping the theory and uses laymans terms.
If you want to speak on the same level I suggest those.


You aren't doing your calculations in absolute temperatures .







This is why you aren't seeing the proportionality of density and temperature correctly. Doing the calculation for density requires this, don't forget in metric units you have a nice 273 degree buffer in there making small temperature changes not seem as large percentage wise. 
Honestly man, this is just a technical discussion, not where you come and tell me what level I am on. For what its worth, I have Incropera sitting on my desk, and as far as the rest of them, same thing, different publisher. To come in here and post twice, both overlooking major parts of the theory behind this, and to tell me that I can't engineer because I didn't "take tests to put food on the table", or I don't have them same size stack of books of you, is ridiculous. Congrats on getting an A in IC Engines class, I did too.
Again, temperatures must be on absolute scale for a 10% decrease in temp to result in a 10% power increase, but its still true. Heres some graphs I made really quick of a 1.8L engine @ 4,500 rpm and 20psi, plotted with different intake temperatures, notice how the graph of mass flow and density has the exact same shape. Again, this goes back to the equations I posted on I think the 2nd page.










_Modified by thom337 at 10:51 AM 9-2-2009_


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## thom337 (Oct 13, 2007)

And before anyone decides to say it, yes the turbo must be capable of achieving shaft speeds necessary to generate and maintain the 20psi in the graphs after the charge has been cooled.


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## thom337 (Oct 13, 2007)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
Despite the "controlled" volume of a motor setup, a bigger turbo DOES flow more VOLUME of air than a smaller one. The why is obviously related to the size of the wheel. When you calculate roughly what a pump is capable of flowing impeller size and # of blades is used to determine the flow rate...which is precisely why an HTA turbo flows more than a standard GT turbo. There is more surface area on the comp wheel, so with each revolution it throws more air.
_Modified by [email protected] at 7:04 AM 9-2-2009_

It is sucking in more volume of atmospheric air, but when it throws it out, it reaches a restriction (either the engine or the air in front of it) and slows down. Diffusing the high velocity air coming off of the compressor blades causes stagnation and leads to a static pressure rise. So, the exit cfm is capped by the volumetric flow of the engine, so the cfm entering the compressor must stagnate on exit and this gives us "boost".


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## HSTuning (Jul 1, 2009)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
It is sucking in more volume of atmospheric air, but when it throws it out, it reaches a restriction (either the engine or the air in front of it) and slows down. Diffusing the high velocity air coming off of the compressor blades causes stagnation and leads to a static pressure rise. So, the exit cfm is capped by the volumetric flow of the engine, so the cfm entering the compressor must stagnate on exit and this gives us "boost".

Exactly, so the confusion I think lies in what do you wanna call the increased volume of air that entered the turbo, and now exits the turbo. If you cram 2000cfm of incoming air into a 1000cfm space it's still 1000cfm, just at a higher density. If a ko3s can pull in 1000cfm it'll still fill the 1000cfm space but it won't be as dense a charge.


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## [email protected] (Oct 23, 2008)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
Exactly, so the confusion I think lies in what do you wanna call the increased volume of air that entered the turbo, and now exits the turbo. If you cram 2000cfm of incoming air into a 1000cfm space it's still 1000cfm, just at a higher density. If a ko3s can pull in 1000cfm it'll still fill the 1000cfm space but it won't be as dense a charge.

Think about engine velocities... If the engine is expelling only cylinder volume in an escalating scale, how would it have the energy to drive the comp to keep up and make power?


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## thom337 (Oct 13, 2007)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
Think about engine velocities... If the engine is expelling only cylinder volume in an escalating scale, how would it have the energy to drive the comp to keep up and make power?

Just because it is expelling the cylinder volume doesn't mean it isn't a very high mass of gasses (now we have our air mass + our fuel mass), at a very high temperature. Once the volumetric constraint of the closed cylinder is removed, they can of course expand to the new volume they are in. They will now flow towards the area of less pressure (accross the turbine or through the wastegate or perhaps a mixture of the two...maybe out your exhaust mani leaks too







). The volumetric flow OUT of the cylinder is more free, and is basically controlled by the volume flow accross the turbine at the turbine pressure ratio you are operating at / any restrictions present in the system. Just because you are emptying a volume, doesn't mean there are any constraints on what is contained in that volume, in this case a very dense and very hot mixture, which is being forced out of the cylinder by the piston / by its own pressure balance.


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## HSTuning (Jul 1, 2009)

*Re: (thom337)*

^right. The volume in the cylinder changes entirely from an air + fuel mix at 30 psi to a burnt mix, exponentially hotter and more pressurized than when it entered, and when the exhaust valve opens it's obviously going to exit with greater force than when it was crammed into the cylinder, thus the increasing speed of the shaft.


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## [email protected] (Oct 23, 2008)

*Re: (thom337)*


_Quote, originally posted by *thom337* »_
Just because it is expelling the cylinder volume doesn't mean it isn't a very high mass of gasses (now we have our air mass + our fuel mass), at a very high temperature. Once the volumetric constraint of the closed cylinder is removed, they can of course expand to the new volume they are in. They will now flow towards the area of less pressure (accross the turbine or through the wastegate or perhaps a mixture of the two...maybe out your exhaust mani leaks too







). The volumetric flow OUT of the cylinder is more free, and is basically controlled by the volume flow accross the turbine at the turbine pressure ratio you are operating at / any restrictions present in the system. Just because you are emptying a volume, doesn't mean there are any constraints on what is contained in that volume, in this case a very dense and very hot mixture, which is being forced out of the cylinder by the piston / by its own pressure balance. 

Never said it wasnt. On the contrary, I did say it on a couple of occasions. It will be charged. It has to be (last time I checked, there's not much disparity between density of air and CO). But the point is, lets give up on the idea of an engine as static volume in regards to the relation of compressor and engine /end



_Modified by [email protected] at 12:40 PM 9-2-2009_


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## turbeau3 (Jul 17, 2006)

*Re: ([email protected]com)*

mentally exhausting.....


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## thom337 (Oct 13, 2007)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
Never said it wasnt. On the contrary, I did say it on a couple of occasions. It will be charged. It has to be (last time I checked, there's not much disparity between density of air and CO). But the point is, lets give up on the idea of an engine as static volume in regards to the relation of compressor and engine /end
_Modified by [email protected] at 12:40 PM 9-2-2009_

I still think it is a good way to model the effects on the intake side of the engine. You can hook up mass flow sensors or perhaps pitot tubes on the suction side and take some steady state data (or do transients and use really high sample rate/ response temperature and pressure measuring devices), and real life performance really does closely match the modeling procedures I've been talking about. It is very much accepted as the method for modeling mass flow into the engine, and there are numerous books that use that model. Using this model also drives people away from the whole "my turbo flows X cfm" methods of talking about performance, and drives people to consider the effects of changing compressor efficiency and pressure ratios on their setup to achieve the best performance. These are good ideas, and they work on paper and in practice.


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## Hudy_cz (Jan 3, 2009)

*Inlet*

Hello. What is the difference, between the inlets?








and this








Why are they different?


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## 20aeman (Jun 8, 2006)

the second one is an anti-surge housing.
Kills a little compressor efficiency but keeps the turbo from surging if it's susceptible to it on your setup.


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## RickHdz36 (Sep 3, 2009)

*Re: (thom337)*

i just put my stage 2 turbo kit its running off the stock dv so im only pushing 8psi until i upgrade, but when i hit about 4.5 and higher and release the gas the turbo flutters. is this because the stock dv cant hold all that pressure or what?? any help please??


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## andy'sgti03 (Nov 16, 2008)

*Re: (04VDubGLI)*

What are you asking for the APR FMIC?


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## dubinsincuwereindiapers (Jan 16, 2008)

*Re: (RickHdz36)*


_Quote, originally posted by *RickHdz36* »_i just put my stage 2 turbo kit its running off the stock dv so im only pushing 8psi until i upgrade, but when i hit about 4.5 and higher and release the gas the turbo flutters. is this because the stock dv cant hold all that pressure or what?? any help please??
wrong thread dork http://****************.com/smile/emthdown.gif


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## paxter (Dec 20, 2005)

*Re: (dubinsincuwereindiapers)*

I really love this thread, bump for more info


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## McVee (Nov 20, 2009)

so was there actually an agreed upon conclusion?

the arguement (and what i want to know) was basically will you get more mass air flow (therfore power) with a GT30R running at 5psi @2000rpm, than you would with a K03 running also at 5psi @2000rpm, if the intake temps are the same, and you ignore effieciencies and the different restrictions on the exhaust flow etc etc.???

From what i've read of this thread, some people are saying that no, pyshics says you will not get any more mass air flow because the volume of the engine is fixed. 

well it may be correct i don't know, but it sounds like a complete over simplification (in terms of the explanation). 

It's arguing a dynamic result with a single static fact.

Volume might be fixed at one point in time, but you do not get any power at one point in time, as power is dependant on time. And over time, your engine is accelerating, and if one engine is accelerating quicker than another engine, and the boost/pressure of the air is the same, well the engine that is accelerating quicker will have a higher mass flow rate.

So that is why i can see the logic in it being possible to have more power at the same boost pressure if you have a bigger turbo.

Anyone help me out here?


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## thom337 (Oct 13, 2007)

McVee said:


> so was there actually an agreed upon conclusion?
> 
> the arguement (and what i want to know) was basically will you get more mass air flow (therfore power) with a GT30R running at 5psi @2000rpm, than you would with a K03 running also at 5psi @2000rpm, if the intake temps are the same, and you ignore effieciencies and the different restrictions on the exhaust flow etc etc.???


From a compressor standpoint ,if a K03 and a GT30R are flowing at the same pressure and temperature (and same volume, ie RPM...turbine effects aside) they are by definition flowing the same mass flow.The point of the thread was that mass flow is a direct function of temperature and pressure (ie if you drop your absolute temperature by 10% with everything else held constant, mass flow will go up 10%)...and also that a compressor should not simply be rated as "xxx cfm" without stating any information regarding density (temp and pres) at that flow. As we all know, in reality a GT30R can flow more mass air than a K03 because it is more efficient...it also benefits from a less restrictive turbine, so under cam overlap at the same mass flow the GT30 will have much less residual burned gas in the cylinder.




McVee said:


> Volume might be fixed at one point in time, but you do not get any power at one point in time, as power is dependant on time. And over time, your engine is accelerating, and if one engine is accelerating quicker than another engine, and the boost/pressure of the air is the same, well the engine that is accelerating quicker will have a higher mass flow rate.
> 
> So that is why i can see the logic in it being possible to have more power at the same boost pressure if you have a bigger turbo.
> 
> Anyone help me out here?


Not sure where to start here... the most basic way to determine power at one point is to take instantaneous torque and speed and calculate it, so yes there is a power at individual points in time. In an IC engine, the power is usually calculated using a filtered engine speed (it is constantly undergoing accelerations and decelerations) and an averaged torque. 

In terms of the acceleration stuff...I'm not sure what you're getting at. The rate at which the engine speed is changing determines the rate at which the volumetric flow changes, there by the rate at which mass flow is changing. Can you expound more on what you're saying in relation to that?


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## McVee (Nov 20, 2009)

thom337 said:


> Not sure where to start here... the most basic way to determine power at one point is to take instantaneous torque and speed and calculate it, so yes there is a power at individual points in time. In an IC engine, the power is usually calculated using a filtered engine speed (it is constantly undergoing accelerations and decelerations) and an averaged torque.


well yes that's one way to calculate power (notice it uses speed which is a function of time), but i think i was just saying (and i was really just thinking out loud), was that power only exists over a period of time. torque can exist statically, but power requires the engine revolutions as the formula shows. a watt is a joule being produced over the period of one second. in an instantaneous moment, there is zero joules being created. that's all i was saying. probably has nothing to do with this arguement though 



thom337 said:


> In terms of the acceleration stuff...I'm not sure what you're getting at. The rate at which the engine speed is changing determines the rate at which the volumetric flow changes, there by the rate at which mass flow is changing. Can you expound more on what you're saying in relation to that?


i was just giving an explanation as to why i thought the reason others were giving about the power being the same due to the fixed volume, was wrong or misleading. it seems people are oversimplifying the analogy by stating a static fact (volume, pressure, temperature), to determine the dynamic result (mass flow rate). The volume is not fixed, it is increasing with time, and hence i do not think you can make a direct corelation (at least without more explanation)


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## thom337 (Oct 13, 2007)

McVee said:


> i was just giving an explanation as to why i thought the reason others were giving about the power being the same due to the fixed volume, was wrong or misleading. it seems people are oversimplifying the analogy by stating a static fact (volume, pressure, temperature), to determine the dynamic result (mass flow rate). The volume is not fixed, it is increasing with time, and hence i do not think you can make a direct corelation (at least without more explanation)


 Volume flow is what it is...volume of air moving per a time period. It is of course averaged typically as the flow into/out of the cylinder is accelerating/decelerating at various points throughout the valve event. The speed-density method is a completely valid calculation and is used everywhere in industry to calculate normalized mass flow in an engine. As I said in a previous post, I have done plenty of dyno testing where hot mass sensors are used and correlate very accurately to calculations performed using speed density. If you want to get into the nitty gritty you can bust out some Navier-Stokes flow field equations, but you will quickly find without a computer it is very painful...and even with that you end up getting essentially the same thing as you would with speed density and an accurate VE map.


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## 04VDubGLI (May 20, 2005)

http://www.kennebell.net/techinfo/general-info/SC_efficiency.pdf

That's all I need to add to this at this point. I recall fighting in the past about how CFM determines the power output of a supercharger/turbo and that not being taken - though it's correct still.


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## thom337 (Oct 13, 2007)

04VDubGLI said:


> http://www.kennebell.net/techinfo/general-info/SC_efficiency.pdf
> 
> That's all I need to add to this at this point. I recall fighting in the past about how CFM determines the power output of a supercharger/turbo and that not being taken - though it's correct still.


Mass flow determines power output...period. Not volume flow. You can have two jars of air side by side, one at one temperature and pressure and the other at another temperature and pressure and they can have completely different masses. The article basically says exactly what I'm saying. Volume flow into and out of a turbo is not the same, MASS flow is the same. Fitting the same mass into a smaller volume means there must be a temperature and pressure rise.

You can rate a turbo's suction side volumetric flowrate and get a fairly good idea of the mass its flowing, so long as atmospheric density stays relatively constant...if it doesn't (ie at altitude vs sea level) you can have some fairly different mass flows. Where people really get into trouble is looking at two compressor maps where there are lines existing above the volume flow axis, and even if the efficiencies are completely different people call them both "xxx CFM" turbos. This is a terrible way to describe the output of a turbo, as this volume flow corresponds to the volumetric consumption of the engine, and without giving regard to efficiency it tells you very little. Garrett offers compressor maps in lb/min, and uses some basic standard assumptions to be able to do that....this I can live with as it puts the emphasis back on mass and not volume.


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## Bierce IV (Apr 5, 2010)

MY car just hit 80k miles, was wondering if it was worth getting chip for k03s or just swap out k04 then tune,
Current Mods:
42 DD 3" DP(Street)
42 DD 2.5" Cat (Street)
Custom SAI
ECS stage 1 clutch coming
forge 007 DV

And also should i grab a FMIC?


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