# 2.5'' or 3'' piping??



## swapthis (Nov 21, 2006)

alright here a quick question i currently have a st1 kinetic turbo kit. t3/t4 60 trim 2.5 downpipe etc. im currently down south in school. my dad going to put a FMIC, so hes going to make custom piping for it so my question is should i tell him to do a 2.5'' piping or 3''?? oh.. yea its for my 12v vr6


_Modified by swapthis at 4:44 PM 4-17-2008_


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## 01VRSIXER (Mar 31, 2004)

*Re: 2.5'' or 3'' piping?? (swapthis)*

2.5" is fine, you could even go smaller if you don't plan on running alot of boost.


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## elitist (Apr 18, 2006)

*Re: 2.5'' or 3'' piping?? (01VRSIXER)*

2.25 is ok too
less boost pressure loss


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## bjtgtr (Dec 13, 2006)

*Re: 2.5'' or 3'' piping?? (swapthis)*

2.25" on the hot side and 2.5" on the cold side. You should get your dad to make you a new dp too. Use 3" for that http://****************.com/smile/emthup.gif


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## leebro61 (Nov 7, 2001)

*Re: 2.5'' or 3'' piping?? (elitist)*


_Quote, originally posted by *elitist* »_2.25 is ok too
less boost pressure loss

Explain please.


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## swapthis (Nov 21, 2006)

*Re: 2.5'' or 3'' piping?? (leebro61)*

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


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## DarkSideGTI (Aug 11, 2001)

*Re: 2.5'' or 3'' piping?? (leebro61)*


_Quote, originally posted by *leebro61* »_
Explain please.









3" piping has more volume to fill than 2.25".
2.25 or 2.5" should be fine. 3" is too big(for your setup) imo.


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## DaKRUSH (Jan 9, 2007)

*Re: 2.5'' or 3'' piping?? (bjtgtr)*


_Quote, originally posted by *bjtgtr* »_2.25" on the hot side and 2.5" on the cold side. You should get your dad to make you a new dp too. Use 3" for that http://****************.com/smile/emthup.gif 

wouldn't it make more sense to do it the other way around... having a slightly bigger pipe off the turbo would help to "suck" the air out and also as the air gets cooled the molecules becoming tighter needing less room. maybe not, im just using simple physics but maybe its different


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## dreadlocks (May 24, 2006)

*Re: 2.5'' or 3'' piping?? (DaKRUSH)*


_Quote, originally posted by *DaKRUSH* »_
wouldn't it make more sense to do it the other way around... having a slightly bigger pipe off the turbo would help to "suck" the air out and also as the air gets cooled the molecules becoming tighter needing less room. maybe not, im just using simple physics but maybe its different 

your not sucking air off a turbo.. smaller diameter before intercooler keeps velocity high when it hits IC and having a larger exit allows the air to evacuate the intercooler quicker.. idea is to reduce the time it takes to charge your pipes/intercooler up.
to the OP, I would suggest 2.25 or 2.25(pre-ic) & 2.5(post-ic) for your setup, either will work fine.. also a full 3" exhaust is going to net you some excellent gains, do it if you can.


_Modified by dreadlocks at 3:27 PM 4-18-2008_


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## rodney_dubs (Mar 2, 2008)

*Re: 2.5'' or 3'' piping?? (DarkSideGTI)*


_Quote, originally posted by *DarkSideGTI* »_
3" piping has more volume to fill than 2.25".
2.25 or 2.5" should be fine. 3" is too big(for your setup) imo.

He meant to explain why there is "pressure loss"... Once the system has gone ~static the pressure loss will be least with the larger piping. It will take longer to get there though due to the volume as mentioned. The difference in volume is pretty minute compared to the mass flow rates of some of these larger turbochargers though.


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## AlbertoB1 (Dec 29, 2007)

Just remember the venturi effect and laws of physics. "The faster air moves, the lower the compression. The slower air moves the more compression" In other words, if you want to keep turbo boost up, use larger pipes on cold side. 2.5" to muffler, 2.75 or 3" muffler inlet, then 2.5" tip to help push air out of exhaust











_Modified by AlbertoB1 at 4:36 PM 4-18-2008_


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## leebro61 (Nov 7, 2001)

*Re: 2.5'' or 3'' piping?? (rodney_dubs)*


_Quote, originally posted by *rodney_dubs* »_
He meant to explain why there is "pressure loss"... Once the system has gone ~static the pressure loss will be least with the larger piping. It will take longer to get there though due to the volume as mentioned. The difference in volume is pretty minute compared to the mass flow rates of some of these larger turbochargers though. 

My point was that most people don't really have any concept of fluid mechanics. The higher the flow velocity, the larger the pressure gradient observed in the flow, meaning the smaller the piping diameter (hence, cross sectional area), the higher the pressure drop. I was just curious how he would explain it. You can't just say "more volume -> less pressure" like you would using the ideal gas law in a closed system. This wasn't meant toward you guys (rodney_dubs or alberto81) as you both seem to know whats up


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## swapthis (Nov 21, 2006)

*Re: 2.5'' or 3'' piping?? (leebro61)*

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


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## bdcoombs (Jul 28, 2002)

*Re: 2.5'' or 3'' piping?? (swapthis)*

let me say first of all ur dad is the shiit. http://****************.com/smile/emthup.gif 
2.5 is fine for all ic pipe. if he is doing that talk him into 3" dp and exhaust while he's at it


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## Issam Abed (Feb 12, 2004)

*Re: 2.5'' or 3'' piping?? (swapthis)*


_Quote, originally posted by *swapthis* »_alright here a quick question i currently have a st1 kinetic turbo kit. t3/t4 60 trim 2.5 downpipe etc. im currently down south in school. my dad going to put a FMIC, so hes going to make custom piping for it so my question is should i tell him to do a 2.5'' piping or 3''?? oh.. yea its for my 12v vr6

I hope this helps.These are some calculations I did:

_Quote, originally posted by *Wizard-of-OD* »_
*Pick your power goal*.For me I am @ 800hp which I will use a conservative value of 1.5 to get the approximate cfm.You can use whatever other values you can find out there.Some use 1.2,others use 1.7
*800hp ~= 1200cfm*
Now you want to keep the velocity of the air travelling through the intercooler piping below *0.4 Mach* = 0.4 (1128 ft/s) = 451.2 ft/s.So what good is this information without any formula's?Well lets calculate the Velocity of air inside of 2" pipe,2.5" pipe & 3" pipe.
*Velocity = (cfm value/ Area of piping)*
*@ 2" we have:*
Velocity = (1200'^3/min x 1 min/60s) */* pi(((2" x 1ft/12")/2)^2)
Velocity = 916.7 ft/s > 0.4 Mach








*@ 2.5" we have :*
Velocity = (1200'^3/min x 1 min/60s) */* pi(((2.5" x 1ft/12")/2)^2)
Velocity = 586.7 ft/s ...close but still > 0.4 Mach
*@ 2.75" we have:*
Velocity = (1200'^3/min x 1 min/60s) */* pi(((2.5" x 1ft/12")/2)^2)
Velocity = 484.8 ft/s ~= 0.4 Mach
*@ 3" we have :*
Velocity = (1200'^3/min x 1 min/60s) */* pi(((3" x 1ft/12")/2)^2)
Velocity = 407.4 ft/s < 0.4 Mach http://****************.com/smile/emthup.gif


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## Weiss (Jun 21, 2004)

*Re: 2.5'' or 3'' piping?? (Wizard-of-OD)*


_Quote, originally posted by *Wizard-of-OD* »_I hope this helps.These are some calculations I did:
Pick your power goal.For me I am @ 800hp which I will use a conservative value of 1.5 to get the approximate cfm.You can use whatever other values you can find out there.Some use 1.2,others use 1.7
800hp ~= 1200cfm
Now you want to keep the velocity of the air travelling through the intercooler piping below 0.4 Mach = 0.4 (1128 ft/s) = 451.2 ft/s.So what good is this information without any formula's?Well lets calculate the Velocity of air inside of 2" pipe,2.5" pipe & 3" pipe.
Velocity = (cfm value/ Area of piping)
@ 2" we have:
Velocity = (1200'^3/min x 1 min/60s) / pi(((2" x 1ft/12")/2)^2)
Velocity = 916.7 ft/s > 0.4 Mach
@ 2.5" we have :
Velocity = (1200'^3/min x 1 min/60s) / pi(((2.5" x 1ft/12")/2)^2)
Velocity = 586.7 ft/s ...close but still > 0.4 Mach
@ 2.75" we have:
Velocity = (1200'^3/min x 1 min/60s) / pi(((2.5" x 1ft/12")/2)^2)
Velocity = 484.8 ft/s ~= 0.4 Mach
@ 3" we have :
Velocity = (1200'^3/min x 1 min/60s) / pi(((3" x 1ft/12")/2)^2)
Velocity = 407.4 ft/s < 0.4 Mach 

So does this mean you want to be as close to .4 Mach as possible for optimum efficiency and the quickest spool??


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## Weiss (Jun 21, 2004)

*Re: (AlbertoB1)*


_Quote, originally posted by *AlbertoB1* »_Just remember the venturi effect and laws of physics. "The faster air moves, the lower the compression. The slower air moves the more compression" In other words, if you want to keep turbo boost up, use larger pipes on cold side. 2.5" to muffler, 2.75 or 3" muffler inlet, then 2.5" tip to help push air out of exhaust








_Modified by AlbertoB1 at 4:36 PM 4-18-2008_

The problem with bottlenecking the exhaust in an effort to increase velocity in a turbocharged application is that people don't take into account the pressure built up within it that is restricting the turbine housing's ability to evacuate the exhaust gas. It sounds good on paper, but as pressure exponentionally increases the restriction used in order to increase velocity now turns against us and becomes just a restriction and will not move the exhaust gas out as fast as without the increased pressure.


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## Issam Abed (Feb 12, 2004)

*Re: 2.5'' or 3'' piping?? (Weiss)*


_Quote, originally posted by *Weiss* »_
So does this mean you want to be as close to .4 Mach as possible for optimum efficiency and the quickest spool??


You have to look @ what your compressor for the turbocharger is rated @.You do not want the air going through the intercooler piping to go supersonic.


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## [email protected] (Apr 25, 2007)

*Re: 2.5'' or 3'' piping?? (Wizard-of-OD)*


_Quote, originally posted by *Wizard-of-OD* »_
You have to look @ what your compressor for the turbocharger is rated @.You do not want the air going through the intercooler piping to go supersonic.

About 300 ft/sec through the throttle is something to avoid as well, I'll confirm that number later.


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## Issam Abed (Feb 12, 2004)

*Re: 2.5'' or 3'' piping?? ([email protected])*


_Quote, originally posted by *[email protected]* »_
About 300 ft/sec through the throttle is something to avoid as well, I'll confirm that number later. 

Since when did you become a Mech.Eng?


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## [email protected] (Apr 25, 2007)

*Re: 2.5'' or 3'' piping?? (Wizard-of-OD)*


_Quote, originally posted by *Wizard-of-OD* »_
Since when did you become a Mech.Eng?

Since when did Civil Eng's know anything about M.E.?







A throttle is a simple velocity control device. And all these values are from Maximum Boost.


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## Issam Abed (Feb 12, 2004)

*Re: 2.5'' or 3'' piping?? ([email protected])*


_Quote, originally posted by *[email protected]* »_
Since when did Civil Eng's know anything about M.E.?







A throttle is a simple velocity control device. And all these values are from Maximum Boost. 

Since I took M.E. for 2 years and realised why learn what you allready know and those values are straight out of my Fluids II notes.








hurry up and scan the throttle body article. http://****************.com/smile/emgift.gif


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## [email protected] (Apr 25, 2007)

*Re: 2.5'' or 3'' piping?? (Wizard-of-OD)*


_Quote, originally posted by *Wizard-of-OD* »_
Since I took M.E. for 2 years and realised why learn what you allready know and those values are straight out of my Fluids II notes.








hurry up and scan the throttle body article. http://****************.com/smile/emgift.gif 

You already knew system dynamics, kinematics, material science, heat transfer, and thermodynamics BEFORE your first two years of M.E. undergrad as well as fluid dynamics? I find that hard to believe. And I can see why you switched to Civil, it has so much to do with your chosen profession and interests.







I'll get the throttle info later, like I said, it's in Maximum Boost.


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## Issam Abed (Feb 12, 2004)

*Re: 2.5'' or 3'' piping?? (Ad[email protected])*


_Quote, originally posted by *[email protected]* »_
You already knew system dynamics, kinematics, material science, heat transfer, and thermodynamics BEFORE your first two years of M.E. undergrad as well as fluid dynamics? I find that hard to believe.

What you have just listed are all courses taken in 1st & 2nd year of Mechanical Engineering.Only Thermodynamics II is taken in 3rd year...
MechanicsI - Statics
Mechanics II - Dynamics
Thermo I - involves heat transfer btw
Thermo II - can be taken as an engineering elective
Fluids I - 
Fluids II
The only course that Civil Engineers take that is different is "Materials Science" which we just call "materials" where we anaylyse stress points of Steel (sounds familiar?) ,concrete aggregate,wood,etc
Its a pretty intense course unlike the laughable materials you guys learn.
And before you run off and say that ME is better....stop in your tracks.I did both and Civil is better....

_Quote, originally posted by *[email protected]* »_I'll get the throttle info later.

Thanks.


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## [email protected] (Apr 25, 2007)

*Re: 2.5'' or 3'' piping?? (Wizard-of-OD)*


_Quote, originally posted by *Wizard-of-OD* »_
What you have just listed are all courses taken in 1st & 2nd year of Mechanical Engineering.Only Thermodynamics II is taken in 3rd year...
MechanicsI - Statics
Mechanics II - Dynamics
Thermo I - involves heat transfer btw
Thermo II - can be taken as an engineering elective
Fluids I - 
Fluids II
The only course that Civil Engineers take that is different is "Materials Science" which we just call "materials" where we anaylyse stress points of Steel (sounds familiar?) ,concrete aggregate,wood,etc
Its a pretty intense course unlike the laughable materials you guys learn.
And before you run off and say that ME is better....stop in your tracks.I did both and Civil is better....

Thanks.


No, you didn't do both, you admitted you quit ME after 2 years. Apparently your school teaches 3000 level classes first then goes back to core classes for junior and senior year.







Statics and dynamics and kinematics and Thermo 1 are 2000 level classes, Thermo 2 and heat transfer are 3000 level, fluids is 3000, mechanics of materials is 3000. Better would be personal opinion, and our material is hardly laughable. The fact that you would describe my curriculum as laughable shows that you have an inflated ego about your own accomplishments. But you think rotaries are reliable.







Again, if you're so into cars, why would you go into Civil if your business is automobiles. Last I checked, civil engineers don't design cars, and mechanical engineers don't design bridges and roads. I seem to remember you IM'ing me a few weeks ago with a thumbsup about being an M.E. Regardless, this isn't a contest like it somehow always is for you. I don't discredit your work, which wouldn't be hard to do, and you don't know the quality of mine, so leave the personal issues aside. 
And I looked it up, you don't want to exceed 300 ft/sec through the throttle to maintain acceptable flow losses.


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## leebro61 (Nov 7, 2001)

*Re: 2.5'' or 3'' piping?? ([email protected])*

Issam, are your classes not calculus based?
In our curriculum, you need Calc 1/2/3/4 to begin taking energy type classes (fluids/heat transfer/thermo). How could you be taking those classes in the first and second semesters? What school did/do you go to? I'm sure you could find the ME course outline online and post it here.
Also, what is the significance of M = 0.4. I have in my head a guess, but I'd like to hear your answer first.


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## Devin @ Kinetic (Apr 16, 2007)

*Re: 2.5'' or 3'' piping?? (dreadlocks)*


_Quote, originally posted by *dreadlocks* »_
your not sucking air off a turbo.. smaller diameter before intercooler keeps velocity high when it hits IC and having a larger exit allows the air to evacuate the intercooler quicker.. idea is to reduce the time it takes to charge your pipes/intercooler up.
to the OP, I would suggest 2.25 or 2.25(pre-ic) & 2.5(post-ic) for your setup, either will work fine.. also a full 3" exhaust is going to net you some excellent gains, do it if you can.

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


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## jda487 (Apr 10, 2008)

*Re: 2.5'' or 3'' piping?? ([email protected])*

moar science less argue please.
Good thread, I like to see actual numbers and scientific reasoning for choices.


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## [email protected] (Apr 25, 2007)

*Re: 2.5'' or 3'' piping?? (leebro61)*


_Quote, originally posted by *leebro61* »_
Also, what is the significance of M = 0.4. I have in my head a guess, but I'd like to hear your answer first.









Rapidly increasing drag with velocities higher than that is the reason to avoid it. The drag not only slows the velocity but adds heat to the fluid in question.


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## leebro61 (Nov 7, 2001)

*Re: 2.5'' or 3'' piping?? ([email protected])*

Adds heat? Static Temperature is going to decrease with increasing mach number (assuming the flow is ~adiabatic). Also, the mach numbers calculated are average mach numbers (as based off of average velocities). Does the theory say to keep the maximum below 0.4 or the average below 0.4?


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## [email protected] (Apr 25, 2007)

*Re: 2.5'' or 3'' piping?? (leebro61)*

And why would you assume adiabatic? lol The calculated numbers would be max, since obviously the airflow rate isn't constant at the volume/mass needed to make peak power at all rpms.


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## CDJetta (May 11, 2004)

*Re: 2.5'' or 3'' piping?? ([email protected])*

You guys make me want to switch from computer science to ME.


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## leebro61 (Nov 7, 2001)

*Re: 2.5'' or 3'' piping?? ([email protected])*

I would assume adiabatic because the temperature inside the pipe is probably very similar to the temperature in the engine bay (we aren't talking about the intercooler here). Without a significant temperature difference, there won't be much heat transfer, hence adiabatic. I don't mean max per RPM, I mean max per the velocity profile.


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## Issam Abed (Feb 12, 2004)

*Re: 2.5'' or 3'' piping?? (swapthis)*


_Quote, originally posted by *[email protected]* »_
Apparently your school teaches 3000 level classes first then goes back to core classes for junior and senior year.







Statics and dynamics and kinematics and Thermo 1 are 2000 level classes, Thermo 2 and heat transfer are 3000 level, fluids is 3000, mechanics of materials is 3000.
 







Now your going to tell me about my curriculum?Get a clue Adam....

_Quote, originally posted by *leebro61* »_Issam, are your classes not calculus based?

Hey Lee,yes they are.
We need Cal IV (4th semester) to take Thermo II.Thermo I/Fluids I you only need CalII as a pre-req.

_Quote, originally posted by *leebro61* »_I would assume adiabatic because the temperature inside the pipe is probably very similar to the temperature in the engine bay (we aren't talking about the intercooler here). Without a significant temperature difference, there won't be much heat transfer, hence adiabatic. I don't mean max per RPM, I mean max per the velocity profile.

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


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## [email protected] (Apr 25, 2007)

*Re: 2.5'' or 3'' piping?? (Wizard-of-OD)*


_Quote, originally posted by *Wizard-of-OD* »_ 







Now your going to tell me about my curriculum?Get a clue Adam....

Hey Lee,yes they are.
We need Cal IV (4th semester) to take Thermo II.Thermo I/Fluids I you only need CalII as a pre-req.
http://****************.com/smile/emthup.gif 

No, I'm telling you about the curriculum of my program that I'm in now, not classes you didn't take. What about Lin Diff Eq, Lin Algebra, Controls, I guess you take those at the end of whatever ME program you were in too.








The air/fluid isn't adiabatic, when the car is underway, there's plenty of fresh air moving through the engine bay, not to mention the thermal absorption of the piping, giving different temps along the inside of the wall as compared to flow in the middle. As soon as you put more heat into the charge air, the heat transfer starts.


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## leebro61 (Nov 7, 2001)

*Re: 2.5'' or 3'' piping?? ([email protected])*

They model turbines (gas/steam) in the industry as adiabatic, for our purposes, any heat loss is negligible at best. Either way it doesn't matter, so long as the total temperature doesn't increase, the static temperature isn't going to increase from friction. Are you familiar with Fanno and/or Rayleigh flow?


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## Issam Abed (Feb 12, 2004)

*Re: 2.5'' or 3'' piping?? ([email protected])*


_Quote, originally posted by *[email protected]* »_
No, I'm telling you about the curriculum of my program that *I'm in now*, not classes you didn't take. What about Lin Diff Eq, Lin Algebra, Controls, I guess you take those at the end of whatever ME program you were in too.









Key phrase...as in taking not took.I allready have my B.Eng.I know what courses I took and what courses I did not take.Linear Algebra I took when I was 16 @ A-levels bud.

_Quote, originally posted by *leebro61* »_They model turbines (gas/steam) in the industry as adiabatic, for our purposes, any heat loss is negligible at best. Either way it doesn't matter, so long as the total temperature doesn't increase, the static temperature isn't going to increase from friction. Are you familiar with Fanno and/or Rayleigh flow?

Lee your wasting your breath...


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## [email protected] (Apr 25, 2007)

*Re: 2.5'' or 3'' piping?? (Wizard-of-OD)*


_Quote, originally posted by *leebro61* »_They model turbines (gas/steam) in the industry as adiabatic, for our purposes, any heat loss is negligible at best. Either way it doesn't matter, so long as the total temperature doesn't increase, the static temperature isn't going to increase from friction. Are you familiar with Fanno and/or Rayleigh flow?

Key word: model. That's like saying there's no heat given off by a turbine ever in the real word. Yes the heat caused by drag in the pipe is minimal, but it exists as well as the slowing of velocity along the pipe wall. 


_Quote, originally posted by *Wizard-of-OD* »_
Key phrase...as in taking not took.I allready have my B.Eng.I know what courses I took and what courses I did not take.Linear Algebra I took when I was 16 @ A-levels bud.


No, I already took every class I named.







You do have your BSE, but it's in Civil, not Mechanical. I took plain Algebra in jr high too, not LINEAR algebra. We're having a discussion Issam, if you can't contribute without your typical attempts at belittling, then just hit the back button.


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## Issam Abed (Feb 12, 2004)

*Re: 2.5'' or 3'' piping?? ([email protected])*


_Quote, originally posted by *[email protected]* »_if you can't contribute without your typical attempts at belittling, then just hit the back button

Attempts @ belittling?Your the same person 4 posts ago that stated you have the ability to discredit my work....so from now on I urge you to do so.

_Quote, originally posted by *[email protected]* »_You do have your BSE, but it's in Civil, not Mechanical.

Ok?Still get paid to do "mechanical" work and "civil" work http://****************.com/smile/emthup.gif 
Back to the topic @ hand....


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## leebro61 (Nov 7, 2001)

*Re: 2.5'' or 3'' piping?? ([email protected])*


_Quote, originally posted by *[email protected]* »_
Key word: model. 

Second key word: negligible.
Are you saying the air in the pipe is heated up by heat transfer or it looses heat to the surroundings? In other words, what is the directionality of the transfer.


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## [email protected] (Apr 25, 2007)

*Re: 2.5'' or 3'' piping?? (leebro61)*


_Quote, originally posted by *leebro61* »_
Second key word: negligible.
Are you saying the air in the pipe is heated up by heat transfer or it looses heat to the surroundings? In other words, what is the directionality of the transfer.

I'm saying it can go either way, that's the point, it isn't adiabatic. This has nothing to do with selecting size of piping though.


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## Mike0105 (Dec 31, 1999)

*Re: 2.5'' or 3'' piping?? ([email protected])*

You both took bigger and fancier classes then me but I know we're wayyyy off topic here so let's not compare college notes and get to the topic at hand








Mike


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## carbide01 (Jul 12, 2003)

Real-world bottom line: 2.5in will work fine for your setup.


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## killa (Nov 26, 2000)

What size is your TB? Both the 2.5 and 3" will work fine, if T04S compressor then run a 2.5" to the Intercooler, otherwise you'll need a reducer causing a bottleneck.


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## CDJetta (May 11, 2004)

*Re: (carbide01)*

I'm going for 600-650whp.... I should use 3" right?


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## [email protected] (Apr 25, 2007)

*Re: (CDJetta)*


_Quote, originally posted by *CDJetta* »_I'm going for 600-650whp.... I should use 3" right?

Correct.


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## carbide01 (Jul 12, 2003)

*Re: (CDJetta)*


_Quote, originally posted by *CDJetta* »_I'm going for 600-650whp.... I should use 3" right?

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


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## carbide01 (Jul 12, 2003)

*Re: 2.5'' or 3'' piping?? (Wizard-of-OD)*


_Quote, originally posted by *Wizard-of-OD* »_
Key phrase...as in taking not took.I allready have my B.Eng.I know what courses I took and what courses I did not take.Linear Algebra I took when I was 16 @ A-levels bud.

Lee your wasting your breath...

By the way, its "you're", not "your".


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## Issam Abed (Feb 12, 2004)

*Re: (CDJetta)*


_Quote, originally posted by *CDJetta* »_I'm going for 600-650whp.... I should use 3" right?

2.5" to the intercooler and 2.5" to 3" to the throttle body.As Paul said what compressor are you using?It depends on the housing...
The ID of the T04S compressor is 2" so you will need to weld on a transition from 2" ID to 2.5"/3" ID.


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## CDJetta (May 11, 2004)

*Re: (Wizard-of-OD)*

Yeah. I'm still using the T04S Compressor cover. Would I need to cut back the compressor cover pipe extension and put on a bigger one or just make the transition right off of the comp cover? That's what I was going to do with a 2.5" to 3" silicone.


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## killa (Nov 26, 2000)

*Re: (CDJetta)*


_Quote, originally posted by *CDJetta* »_Yeah. I'm still using the T04S Compressor cover. Would I need to cut back the compressor cover pipe extension and put on a bigger one or just make the transition right off of the comp cover? That's what I was going to do with a 2.5" to 3" silicone.

2.5" from the turbo outlet to the Intercooler, make sure that you dont have a cheap one and either 2.5" or 3" to the TB, preferably 3".
http://****************.com/smile/emthup.gif


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## Issam Abed (Feb 12, 2004)

*Re: (CDJetta)*


_Quote, originally posted by *CDJetta* »_Yeah. I'm still using the T04S Compressor cover. Would I need to cut back the compressor cover pipe extension and put on a bigger one or just make the transition right off of the comp cover? That's what I was going to do with a 2.5" to 3" silicone.

Make a smoothe transition.I suggest sourcing an aluminum transition from burns stainless that goes from 2" to 2.5" ID.Weld it onto the compressor cover outlet and just port it for smoothness.
From the transition piece use whatever silicone connectors you want.


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