# Runner length under boost question



## PeOpLeG60T (Jul 5, 2004)

hi !
i dont remind seeing any discussion about this but as i was reading some other thread about SRI's pros and cons i was wondering something...
do the harmonics of the engine' RPM versus runner length stay untouched under boost ?
or the properties of air waves do change under pressurised flow ?
thanks for clearing that up for me


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## TBT-Syncro (Apr 28, 2001)

*Re: Runner length under boost question (PeOpLeG60T)*

Well considering a NA motor is under 14.7 PSI of pressure, a motor with boost added, isnt in any sort of different situation.
so the answer is that runner length, harmonics, gas, flow, etc, is the exact same for a NA car, as a FI car.


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## GTijoejoe (Oct 6, 2001)

*Re: Runner length under boost question (TBT-Syncro)*


_Quote, originally posted by *TBT-Syncro* »_Well considering a NA motor is under 14.7 PSI of pressure, a motor with boost added, isnt in any sort of different situation.
so the answer is that runner length, harmonics, gas, flow, etc, is the exact same for a NA car, as a FI car.

I don't think I agree......
Perhaps I didn't fully understand the question.


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## leebro61 (Nov 7, 2001)

*Re: Runner length under boost question (TBT-Syncro)*

The speed of sound in a "perfect" gas is a function of temperature only. The pressure is basically irrelevant and because of the sonic velocity relationship, small changes in intake air temperature (eg: NA -> intercooled turbo) have negligible impact on harmonic tuning.








When you get into sonic velocity in liquids, the bulk modulus of the material is the main driver and that's a different story...


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## PeOpLeG60T (Jul 5, 2004)

*Re: Runner length under boost question (TBT-Syncro)*

lets say at a 15 psi turbo added , would be twice as N/A air pressure.
is the air in any way having different properties ? such as density and viscosity , way of transfering a wave while under diffrent pressures ?
twice the pressure , about twice the stuff in the same container , would a wave behave diffrently in those 2 diffrent containers ?
i know good amount of physics but im wondering if there culd be diffrence. 
i dont know if you figure out what point im trying to dig tell me if i need to rephrase or something
thanks


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## PeOpLeG60T (Jul 5, 2004)

oh you posted while i was writing , thanks for the info leebro !
i guess it closes the thread heh


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## leebro61 (Nov 7, 2001)

*Re: (PeOpLeG60T)*


_Quote, originally posted by *PeOpLeG60T* »_oh you posted while i was writing , thanks for the info leebro !
i guess it closes the thread heh 

No problem. If you're handy with physics/thermo/calculus, there is a pretty straightforward derivation of the speed of sound... or you can just take my word for it


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## PeOpLeG60T (Jul 5, 2004)

as for harmonics , btw , if you are familiar with runner tuning , is the theory only good if there is a perpendicular wall to reflect the wave back at the valve in order to work correctly?


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## TBT-Syncro (Apr 28, 2001)

*Re: (PeOpLeG60T)*


_Quote, originally posted by *PeOpLeG60T* »_as for harmonics , btw , if you are familiar with runner tuning , is the theory only good if there is a perpendicular wall to reflect the wave back at the valve in order to work correctly?

it still applies regardless of the angle (valve back is rarely perpendicular)


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## GTijoejoe (Oct 6, 2001)

*Re: Runner length under boost question (leebro61)*


_Quote, originally posted by *leebro61* »_The speed of sound in a "perfect" gas is a function of temperature only. The pressure is basically irrelevant and because of the sonic velocity relationship, small changes in intake air temperature (eg: NA -> intercooled turbo) have negligible impact on harmonic tuning.








When you get into sonic velocity in liquids, the bulk modulus of the material is the main driver and that's a different story...


Yep, I'm on top off all that, ....specifically static temp ...Sq rt of (Gamma*R*Ts)







... you know (top of class in compressible aero)....
In my mind I take the OP's question assuming (as he is asking) if the harmonics etc were the same NA vs FI then the manifold design could be the same.... and I don't believe that would be true. 
I imagen the actual waves that form would not be similar amplitudes, although they may travel the same way via the spd of sound, and I think this because how the valves are going to shut colliding with the incoming air which is now pressurized.....
This is just my gears turning, I really don't know the answer....I'm using that stuff you get at your college book store...'engineering intuition'








Discuss/educate/inform I'm thinking about his question correctly


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## leebro61 (Nov 7, 2001)

*Re: Runner length under boost question (GTijoejoe)*

Conceptually it's a difficult thing to visualize (at least for me). Most of my compressible fluids work experience is in external flow (wind blade aero, specifically) and while I did some acoustics, I didn't dive deep into waves. I do recall from some CFD discretization scheme basics that the first order wave equation (dp/dx+a*dp/dt = 0) is dominated by the wave speed (a). I couldn't tell you where amplitude comes in, or if it's even important.
In my opinion, the characteristic changes between a NA and a boosted intake manifold probably aren't drastic enough to require different designs. If the boosted engine is going to make significantly more power, then you would want to size runner diameter and such accordingly, but that's driven by the fluid behavior, not the wave behavior. My thought is that if you see a company marketing a "turbo intake manifold", they are only doing so because people are more likely to buy parts if they think they are better for their application... not because they have some superior understanding of the physics that eludes the rest of us...


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## PeOpLeG60T (Jul 5, 2004)

Marketing !!!
thanks for putting some efforts trying to figureout my interrogations guys.
was wondering this for future manifold design. wondering if optimal runner length would be diffrent for N/A and FI applications. does runner width plays a role into the harmonics of a same length runner ?
would taper runners behave diffrently?
and what would be the values to aim at ? how do we choose to tune to "X" value rpm and not another ? are we aiming at the peak of a hp or torque curve seen on a dyno ? is there a known sweet spot ?
with my understanding , we tune a runner lenght to use the harmonics who appears at the tuned RPM of the engine rigth ? so its really tuned at a specific rpm value so out of tune before and after this value .... am i rigth ?
so on a 16v engine you would like to tune it around 5.5krpm ? not too high to benefit from it


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## GTijoejoe (Oct 6, 2001)

*Re: Runner length under boost question (leebro61)*


_Quote, originally posted by *leebro61* »_
My thought is that if you see a company marketing a "turbo intake manifold", they are only doing so because people are more likely to buy parts if they think they are better for their application... not because they have some superior understanding of the physics that eludes the rest of us...









hahaah








Yes I'm sure that is true in most cases... I would think superior understanding would come from experience and alot of money, like the racing industry.
I guess honestly to answer most of these questions you would probably have to do some of this stuff or something very similar for a living. Without the experience you most likely do not truely know the answer. Of course with the more general questions there are many ppl that would know the answers.
I would agree that in general a manifold design can be used for both FI and NA applications and have a positive effect, but I woudn't doubt you could tweak both differently to gain a little more power/efficiency just a little bit more for both.
The nature of my work place there is just about every type of automotive engineer, I have a buddy that designs intakes and intake manifolds (coincidence enough). By no means is he an 'expert' but he has made many designs which made it to mass production so he does have some experience, I'll be curious to know what his 'opinion' is on the subject. I would think he would know a decent amount about harnomics and waves since those intakes have to be quiet and muffle all that sound while providing good flow, and those mani's have flapper valves.


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## PeOpLeG60T (Jul 5, 2004)

if i see a clearance sale about TURBO flapper valves i'd buy it
but yeah , it could be a good idea to hear from your friend ! you now , sir , have a mission !!


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## slc92 (Feb 9, 2005)

*Re: Runner length under boost question (leebro61)*


_Quote, originally posted by *leebro61* »_ My thought is that if you see a company marketing a "turbo intake manifold", they are only doing so because people are more likely to buy parts if they think they are better for their application... not because they have some superior understanding of the physics that eludes the rest of us...









Very good point. I'm no engineer so what I'll often do is look at what the engineers designed for the cars I work on everyday(Volvos) especially since there are plenty of FI and NA engine variations.
The newer V8 and 3.2L V6 engines are both NA and both use flapper style manifolds. The main purpose as explained in the training manuals is to increase runner length for more torque in the mid range and or to move peak torque down in the rpm band. Even the non-flapper mani's always have longer runners for the NA cars w/ more of a log style for the turbos.
The turbo doesn't need the longer runners, but I always wondered what effect the turbo mani has in and of itself. The other thing I keep in mind was that those motors were designed as a whole either FI or NA. Many FI'd cars on here simply added a turbo to their engine. I would think there is a difference.


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## PeOpLeG60T (Jul 5, 2004)

i heard Porsche is working on a nice variable geometry system for their intakes . shaped like coaxial runners in circular shape , like wrapping around a cynlinder , and constantly modulating the runner lenght by pulling in and out in a circular motion . shaped a bit like a turbo's compressor housing . i like those kinda engineers . this system ensures space saving since the runners arent taking more space in the bay as they lengthens.


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## PeOpLeG60T (Jul 5, 2004)

i also have a vision
been thinking about the benefits of grooving some circular path into the runner's lenght . like into the barrel of a gun . to give a spin to the air before it hits the valve to give a better air-fuel mix into the cylinder.
all of this being hypothetical and fruit of my imagination

could be good in a single intake valve tho... since the spin would hit the seperation between the 2 intake valves onf a 16v .. maybe notch individual intake ports into the head .
just a vision i had and had to write it down here if anyone would be interested in the idea and see if it could have any benefits


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## leebro61 (Nov 7, 2001)

*Re: (PeOpLeG60T)*

I did something similar with a turbo air intake. By putting orthogonal bends in a pipe, you can cause the flow to rotate in the direction the wheel is turning. The pre-swirl trick is something people used to use on centrifugal compressors, probably for oil & gas pumping applications. Will it make a tangible difference... probably not, but it helped with fitment also. In theory you might be able to extend the high rpm pressure capabilities of a compressor slightly further by pre-swirling the inlet


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## EL DRIFTO (Jul 11, 2004)

*Re: (leebro61)*

i'm having visions too so its time to post for swirl & thumb over the end of the garden hose effect
http://www.mototuneusa.com/think_fast.htm
imo: since i'm not an engineer, the VE of factory turbos combined with the VE of the engine results in a torque monster so they make the motor VE higher rpm, in the mani
the width of the runner has no effect on the speed of sound through the air or the target rpm
my math peaks seem to be wrong in the other thread, although i'm using vizard's method, it does show 2 peaks though
unfortunately the engineers i know dont know the diff between a narrow & wideband o2, maybe they just post the wrong info to get to me








i think you'd have to ride the knock sensors & datalog on the dyno to realize the full overall eff. from temp, etc, of a diff mani design
i wonder if you could arrange the inlet pipe of the turbo, in too far into the rubber boot, to get same effect


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## PeOpLeG60T (Jul 5, 2004)

i seen something on Discovery where they were researching on "super tubes" inducing a circular motion in the liquids and it was flowing more than a static fluid


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## GTijoejoe (Oct 6, 2001)

*Re: (PeOpLeG60T)*


_Quote, originally posted by *PeOpLeG60T* »_ it could be a good idea to hear from your friend ! you now , sir , have a mission !!

...I spoke with my buddy today and this is his opinion on the subject, N/a vs FI manifold design.
"The freq. of the waves should be very similar between the two, the amplitudes may be higher with FI, but the focus with dealing with waves is the freq. either way. 
Answering the question more directly, the manifold designs wouldn't/shouldn't be the same. N/A applications can only rely on long runners to build torque, where an FI application will use power adder as an advantage, and then tune the manifold a little differently because of it. Ideal N/A manifold is individual T-bodies open to atmosphere, and that's just not possible with FI applications. 
Plenum size would be the next difference, FI applications should have much larger volumes in some cases"
...at least that is what I remember from our conversation. Take this info as you wish http://****************.com/smile/emthup.gif


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## PeOpLeG60T (Jul 5, 2004)

*Re: (GTijoejoe)*

hah thanks , i kinda forgot about this thread thansk to bring it back up
as for runner lenght , the shorter the runner , the resonance wave rise up and the benefits goes down.
wave 1 have a bigger pulse than the 5th .
how about a good sized plenum and long but really really free flowing runners ? , could benefit from a bigger pulse but with enough width from the runner could perform just like a shorter runner ? because primarily we cut down on runner lenght for a matter of flow in a specific diameter of pipe and also fab and design ease. 
am i rigth ?


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## CDJetta (May 11, 2004)

*Re: (PeOpLeG60T)*

From that calculator you need insanely long runners for 7500rpm resonance tuning. does the shape of the port matter?


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## [email protected] (Jul 2, 2006)

*Re: (CDJetta)*


_Quote, originally posted by *CDJetta* »_From that calculator you need insanely long runners for 7500rpm resonance tuning. does the shape of the port matter?

Port area , cam duration,lift etc need to be taken into the formula also exept for the standard basic engine info
Most standard software require atleast 30 specific data point to make it "accurate"


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## S3.2 (Sep 19, 2009)

*Re: ([email protected])*

Regarding the swirl-spiral effects for intake air: I read somewhere that engineers actually try to avoid this because the fuel doesn't mix well with air. That's why the newer designs have square intake runners. Square runners stop the spiral movement or the air and resist in fuel "padding".
Regarding this effect pre-turbo: It reminds me of some cheap "tornado" ebay propellers which do just that. Only problem is that everyone who tried them only lost Hp.
Regarding long turbo runners: Isn't it strange that every OEM or after market turbo intake is short and every NA long? I mean if the same theory for pulses worked for both NA and FI wouldn't OEM use it?
Sorry for being so negative but IMO it's the hard truth.
Tough s**t iron horse.


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## slc92 (Feb 9, 2005)

*Re: (S3.2)*

What are you being negative about?
I don't think anyone here is trying to prove a point one way or another. Just some good information sharing going on. http://****************.com/smile/emthup.gif 
I'm pretty sure OE manufacturers don't use manifolds w/ long runners on turbo cars b/c they don't need to add daily driving torque. The turbo does that.
My question is always with a car that was originally NA and converted to turbo. Manifold, head, cams, etc. were all designed as a unit on an NA motor. What benefit does the SRI serve besides losing torque if you keep the NA rev. limit. ~6500 (7k chipped)? 
In other words chip tuned 10psi ~300whp or 20psi 400whp setup. Are you going to make more hp at the same boost w/ the SRI under 7krpm? Less power? No change?


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## S3.2 (Sep 19, 2009)

*Re: (slc92)*


_Quote, originally posted by *slc92* »_What are you being negative about?
I don't think anyone here is trying to prove a point one way or another. Just some good information sharing going on. http://****************.com/smile/emthup.gif 
I'm pretty sure OE manufacturers don't use manifolds w/ long runners on turbo cars b/c they don't need to add daily driving torque. The turbo does that.


I thought that the idea was that the intake mani should have runners some 50cm long in order to be "tuned" to the pulses @ 5-7K rpms and that applies also to FI.
If that's the case then I'm sure VAG would have used this in an engine so expensive that puts a SC and a turbo to work together. I don't believe it's a cost issue nor that VAG doesn't know about this.
Then I thought that all people in this thread are very fond of this theory and that with my reply I was being negative.
If this theory is right then when you convert a NA motor to FI then you better leave the intake mani as is, or you will loose Hp if you put a SRI.


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## CDJetta (May 11, 2004)

*Re: (S3.2)*

It depends on a lot of variables. Cam duration/lift, runner length, plenum design, displacement, etc.
The way it all works, as stated above, is that the air works as a sound wave. When the valves close the air can't go through and if we look at air as a sound wave it sends a sound wave back towards the plenum. The plenum works as a "spring" per say and it absorbs the wave but it also pushes it back into the runner. This takes a certain amount of time, the speed of sound. The sound wave will bounce back and forth, gradually getting weaker at each bounce. From what I have read or been told OE manifolds are tuned for the 3rd wave. The reason for this is because if you used the 1st or 2nd wave you'd need REALLY long runner and there are of course size constraints in the engine bay.
The plenum design comes into affect with how much it "springs" back and the back wall of the plenum that is perpendicular to the runners to get a secondary reflection that has a small affect but an affect none the less. You want to make the plenum a certain size depending on NA and FI. NA uses a smaller plenum and FI uses a bigger plenum just going on what I have read. I don't know the math behind that and I'm working on that but the sound wave that comes out of the runners not only gets sprung back because of the plenum "spring" but it also gets reflected off the back side of the plenum which has to be a certain distance away in order to try and get it's affect.
I'm sure S3.2 is mainly going off of dyno graphs where people take a stock lower manifold and slap a box onto it and call it a SRI. These aren't tuned at all. They are just the cheapest and easiest ways of making manifold that is easier to access and is easier to pipe. A long time ago some American companies started making tuned intake manifolds and it's been done on OE cars for a long long time. I'm pretty sure OE manifolds aren't made for top end/race power though. They are probably made for better day to day driving near the middle of the power band. There was a cool site I read the other day that showed a demonstration of how it all worked on a NA car and how you can actually get the wave to hit the valve right at the right moment so that it actually forces are into the combustion chamber instead of it being "sucked" in. This of course would net more power.


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## S3.2 (Sep 19, 2009)

*Re: (CDJetta)*

You drive a TDI: why do diesels have SRIs? Wouldn't they benefit from long runners working with so low rpms? and what about trucks: they have lots of engine bay space and an rpm limiter of some 2.5K...and a SRI!


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## CDJetta (May 11, 2004)

*Re: (S3.2)*

Me driving a TDI has nothing to do with this. The TDI is my daily, it's not what race around with and me driving a TDI doesn't make the calculations wrong...
I never said long = better low range RPM. That's what you said. The length of the runner all depends on what which reflective wave you want to use. If you want to use the 1st or 2nd then you're gunna have one hella long set of runners.
As for diesel engines.... do you know how a diesel engine works? They aren't made for high RPM. All their internals are a ton beefier, the turbos on them are not made to flow high rpm, and the injection pump is usually the main limiting factor because it's all mechanical spinning a mechanical pump to 5+k rpm spells disaster. As you got up in engine sizes the pumps get bigger and once again, spinning a bigger pump at a higher rpm is a no no.
You also have to take into account a lot of diesels don't have throttle bodies. Some do but it's not really needed. Because there's no throttle body then the whole intake system pretty much becomes the plenum. I'm thinking this throws the whole runner length out the door because the chance for the wave to bounce isn't really there so, why make an expensive long runner system that's not really going to do something when you can save money and just make a small manifold.


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## [email protected] (Jul 2, 2006)

*Re: (S3.2)*


_Quote, originally posted by *S3.2* »_You drive a TDI: why do diesels have SRIs? Wouldn't they benefit from long runners working with so low rpms? and what about trucks: they have lots of engine bay space and an rpm limiter of some 2.5K...and a SRI!

If you wanna have the pulse effect
do it right and add correct lenght if you dont have fitment issues.
All OEM turbo these days even run vario intakes with runner lenght or port area vario function.

1.8T have correct runner lenght for its HUGE port size.
FSI 2.0T have vario function on some intake versions.
Basicly all N/A use vario intakes with pulse tune.
and as fot the short runners.
show me one turbo petrol car with short runners from factory.
Even Supra got long runners and got some huge ports.
Working with engine R&D








Our latest 700Hp+ factory V8-T dont have correct runner lenght.
Why?
We couldent fit it and factory HP goal was already reached.



_Modified by [email protected] at 1:37 PM 3-15-2010_


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## S3.2 (Sep 19, 2009)

*Re: ([email protected])*

For the diesels: The longer the runners are the lower rpms they are tuned for. So that's why diesels should have very long runners. And when you are @ WOT it's like having no throttle at all (just like diesels) In that manner diesels do not differ than ottos.
I understand how that there are space constraints especially with V8s and that's why I asked about the trucks. All factory turbo cars have runners 30cm the longest. That's what I call short, compared to NA where they are more than 50cm and fold on top of the cylinder head like the R32. I haven't seen any turbo engines with intakes so long that fold on top of the cylinder heads.
I don't know how to calculate the runner length and take into account so many factors like port size, but I find it difficult to understand how the 1.8T you say has tuned intake being so short compared to the R32.


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## [email protected] (Jul 2, 2006)

*Re: (S3.2)*


_Quote, originally posted by *S3.2* »_For the diesels: The longer the runners are the lower rpms they are tuned for. So that's why diesels should have very long runners. And when you are @ WOT it's like having no throttle at all (just like diesels) In that manner diesels do not differ than ottos.
I understand how that there are space constraints especially with V8s and that's why I asked about the trucks. All factory turbo cars have runners 30cm the longest. That's what I call short, compared to NA where they are more than 50cm and fold on top of the cylinder head like the R32. I haven't seen any turbo engines with intakes so long that fold on top of the cylinder heads.
I don't know how to calculate the runner length and take into account so many factors like port size, but I find it difficult to understand how the 1.8T you say has tuned intake being so short compared to the R32.

R32 have vario intake. dual chamber
Low RPM = long runners
4500rpm+ = short runner 

So at high rpm its just as short as 1.8T


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## swagger rob (Aug 13, 2009)

*Re: Runner length under boost question (leebro61)*

There's too many big words in this thread and I take that as disrespect


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## GTijoejoe (Oct 6, 2001)

*Re: (S3.2)*


_Quote, originally posted by *S3.2* »_Regarding long turbo runners: Isn't it strange that every OEM or after market turbo intake is short and every NA long? I mean if the same theory for pulses worked for both NA and FI wouldn't OEM use it?
Sorry for being so negative but IMO it's the hard truth.
Tough s**t iron horse.


I don't think this is negative, perhaps constructive. 
As previously stated twice or so... the design of FI vs NA would change because of the benefits of FI, so runner length could be decreased because of the added torque of the FI application. I think the same applies to SI engines too, diesels produce more torque by nature similar to FI applications otto engines but the design would be different because of it. 
I think a good comparison would be looking for two similar motor's from the same OE and compare the mani's (that would be interesting)
In general with design, there is always some goal, and than how to achieve that goal with as little $ and investment possible. This being key, because long runners cost $$$ in comparison, not only for material but also processing and die costs. So in general, if you tune your system to achieve your goals with less, than you will do that...
Where as, car ppl like us are always looking for the "most" and "best", which is not always the point in OE design, in addition too, manifold design also can produced increase levels of noise and such, which is something else that would change a manifold design.


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## kevhayward (Mar 13, 2007)

*Re: ([email protected])*


_Quote, originally posted by *[email protected]* »_
show me one turbo petrol car with short runners from factory.


You didn't say how short short is, but these all look short to me.

Audi UR Quattro








Ford Sierra/Sapphire/Escort Cosworth turbo








Renault 5 GT Turbo








My own Polo 1.8T engine








Ford Escort RS Turbo 








Ford 3.0 V6 Normally Aspirated








Ford 2.0 16V normally aspirated








Renault Clio 2.0 16V normally aspirated








Once again, a lot of hot air and maths being thrown about but zero hard proof that a Manifold X is better than Manifold Y.


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## slc92 (Feb 9, 2005)

*Re: (kevhayward)*

Here are some hard #'s that I like.
a) Stock VR manifold tuned for that engine= FREE
b) SRI VR manifold not tuned = $500-$1300.


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## EL DRIFTO (Jul 11, 2004)

*Re: (kevhayward)*


_Quote, originally posted by *kevhayward* »_









from the pics i can see, they look to be tuned to the third & the cozi is probably spinning fast


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## kevhayward (Mar 13, 2007)

*Re: (slc92)*


_Quote, originally posted by *slc92* »_Here are some hard #'s that I like.
a) Stock VR manifold tuned for that engine= FREE
b) SRI VR manifold not tuned = $500-$1300.










How many more times? The VR6 has such long runners because it makes f'ck all torque in normally aspirated form. 
If you add a turbo, you don't need long runners any more. Isn't that obvious by the fact all the major OE turbo makers user short runners on their engines? Or are you saying the OEs are clueless in these matters and should hook you up for the engineering excellence they are clearly lacking?


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## kevhayward (Mar 13, 2007)

*Re: (EL DRIFTO)*


_Quote, originally posted by *EL DRIFTO* »_
from the pics i can see, they look to be tuned to the third & the cozi is probably spinning fast


The Clio's is tuned for sure, but notice the runners don't fold right over the motor like the VR6's does. It's a revvy motor and still makes good torque for a 4 pot 2 litre.
The road spec Cossie was not a fast spinning motor. 
220 Bhp @ 6250 rpm (227 Bhp @5750 after 1994) 
290 N/m @ 3500rpm (@2500rpm after 1994)


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## slc92 (Feb 9, 2005)

*Re: (kevhayward)*


_Quote, originally posted by *kevhayward* »_
How many more times? The VR6 has such long runners because it makes f'ck all torque in normally aspirated form. 
If you add a turbo, you don't need long runners any more. Isn't that obvious by the fact all the major OE turbo makers user short runners on their engines? Or are you saying the OEs are clueless in these matters and should hook you up for the engineering excellence they are clearly lacking?



I'm saying that I think the OE mani is superior to an SRI on a 4k-~6500rpm powerband setup turbo car b/c it was tuned for it and runner compensation is built in vs. a tank welded onto a lower mani that isn't pulse tuned and doesn't compensate for the runner length differences in the head. 
OE clueless? Quite the opposite. They built a manifold for that motor and gave it to you for free w/ the car http://****************.com/smile/emthup.gif


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## S3.2 (Sep 19, 2009)

*Re: (slc92)*


_Quote, originally posted by *slc92* »_
I'm saying that I think the OE mani is superior to an SRI on a 4k-~6500rpm powerband setup turbo car b/c it was tuned for it and runner compensation is built in vs. a tank welded onto a lower mani that isn't pulse tuned and doesn't compensate for the runner length differences in the head. 

Then why do you think one should buy a SRI?

_Quote, originally posted by *slc92* »_
OE clueless? Quite the opposite. They built a manifold for that motor and gave it to you for free w/ the car http://****************.com/smile/emthup.gif 








???
The Renault 5 on the picture has a turbo converted engine transplant from a Clio (NA from the factory). The Clio actually does NOT have SRI (being NA) and the mani might not fold on top of the engine like the R32 but it folds around the plenum, its runners are about 50cm. The OEM Renault 5 turbo engine on the other hand has SRI.
Maybe other factors come to play like transient response (takes longer to fill the long runners from full vacuum to full boost), so factories use SRIs.



_Modified by S3.2 at 2:41 AM 3-18-2010_


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## slc92 (Feb 9, 2005)

*Re: (S3.2)*


_Quote, originally posted by *S3.2* »_
Then why do you think one should buy a SRI?

_Modified by S3.2 at 2:41 AM 3-18-2010_

When the turbo wont fit w/ the stock mani and/or you are shifting the powerband above OE typically seen w/ standalone (higher rev. limit) setups w/ the supporting components to make power at those high rpm levels.
Just my opinion. I'm not an engineer so take it for what it's worth


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## GTijoejoe (Oct 6, 2001)

*Re: (slc92)*


_Quote, originally posted by *slc92* »_
When the turbo wont fit w/ the stock mani and/or you are shifting the powerband above OE typically seen w/ standalone (higher rev. limit) setups w/ the supporting components to make power at those high rpm levels.


This would be true. Higher rpm benefits from the short runners.


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## TBT-Syncro (Apr 28, 2001)

*Re: (slc92)*


_Quote, originally posted by *slc92* »_
I'm saying that I think the OE mani is superior to an SRI on a 4k-~6500rpm powerband setup turbo car b/c it was tuned for it and runner compensation is built in 

i'm skeptical as to how much tuning their is in the stock manifold (although there are lots of poorly designed SRI). There is nothing in the stock manifolds design or construction that leads me to believe that it's anything other than 'the size that fits'.


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## slc92 (Feb 9, 2005)

*Re: (TBT-Syncro)*


_Quote, originally posted by *TBT-Syncro* »_
i'm skeptical as to how much tuning their is in the stock manifold (although there are lots of poorly designed SRI). There is nothing in the stock manifolds design or construction that leads me to believe that it's anything other than 'the size that fits'.

Runner compensation and 3rd pulse tuned. No?


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## EL DRIFTO (Jul 11, 2004)

*Re: (slc92)*


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