Do ITB's really make more power

[///schwartzman]

Yes correction, but either way it would need tuning... For a given rpm range based on area/length of each runner and flow.

http://www.youtube.com/watch?v=SIjBU9tI-Go

I love this topic because it introduces the technology that is still developing now. Variable length runners, variable vane turbos, there is no exact way but you get close and deal with the variance especially true for n/a motors which is why they force-fed motors in the first place.

[jute91]

Here is my thoughts.. If there is ITB's vs. STB (Single Throttle Body) with the same runner lenght and size (comparing when itb setup doesnt contain "collector chamber", let's think it without it first) The main difference is getting more equal air flow to each cylinder. There is always problem if using STB manifold that you should make the manifold that way that every cylinder would have same amount of air. M20 has great intake manifold design for its age. I always think air flow : "Air has will to flow straight" if understand my opinion.


Cylinder 1 and 6 are ones which have The longest distance from TB. and the cylinder 3 and 4 have the shortest. I haven't measured the M20 intake manifold but I think they have little bit different size and lenght runners when comparing the middle ones with the ones on the corner.. But The order in chamber after TB makes also its part of flow. It is much easier way to flow into runners 1 and 6 at the back of the chamber than the runners at right after TB ( 3 and 4) thats because softer turn in air flow. However I have seen some Flow test that have been run to m20 manifold and it says there is no much difference between cylinders.

Second thought when comparin ITB and STB is the manifold design.. ITB has straight tunnel, which makes lower flow resistance than manifold that has bended runners like in stock manifold. But the bended runners may have other properties. They might make the right kind of turbulence which improves air flow at lower RPM. Also Chamber between runners and STB collects all in one and makes vacuum that improves air flow from low rpm to middle rpm.

ITB design to stock m20 885 head is pretty hard because the inlet ports. Everything should be smooth as possible. Check my ITB project that I'm running now...

[Eric]

On the same note, an S38 with a carbon air box and Alpha N would be pretty awesome.

Will

indeed.

[reelizmpro]

Shorter runners aid top end HP and longer runners aid low end torque generally speaking. ITB's have the throttles really close to the intake port and it's a straight shot more or less. There's an air plenum that supplies the trumpets (which aid laminar airflow) with all the air they need. With a manifold, the air must be distributed between the cylinders around bends and corners over a greater distance. I think manifolds are cheaper to make and offer a compromise between low end torque and high power. Whereas ITB's are all about high end HP. It's like stock exhaust manifolds vs headers. If the intake tract cannot keep up with the demands of the engine, then HP will be left on the table so to speak. It's like running an ETA intake manifold on a modified 2.7 i engine. Let's look at an ETA manifold and 325i manifold. If you analyze them both, you'll notice that the ETA manifold has longer-narrow runners while the 325i manifold has shorter-larger runners. Most notice the port size right away but runner length is different as well. The 325i manifold supports a good amount of HP before it starts becoming restrictive since the M20 is still 2 valve per cylinder. With more valves and more RPM, demand for airflow goes up. The S14 came with 46mm ITB's and 48mm ITB's on the 215+HP engines as this engine is all about high end HP, which is why it seems sluggish with typical street driving. Today damn near all engines are multivalve and you see more manufactures use large port manifolds or variable length runner manifolds that offer the best of both worlds. As far as max HP goes, they could be equal if the single throttle body was large enough and the intake manifold short enough. Even then, ITB's would still have better response, they'd just be more complex and expensive.

Eric...that must sound glorious.

[Eric]

Eric...that must sound glorious.

Barry, it sounded nice, but to be honest the S14 sounds better with a carbon airbox. You could hear the difference too at the nurburgring, especially standing outside the corner Brunchen. Because there are more pulses in a 6cyl vs. a 4cyl, the noise is smoother and less boomy. The M3csl sounded cool, but a carbon airbox'd E30 M3 was always the coolest sounding car climbing up the hill.

[Nick_S]

I was under the assumption that longer intake trumpets increase torque and shorter ones increase high-end horsepower. My only good evidence off the top of my head is the intakes for the can-am chaparral race cars were lengthened to increase and flatten torque.

I believe you are correct. Speaking from personal experience here...my old SVT Focus came with a dual stage intake manifold that would switch from long runner, to a short runner intake to aid in low end torque and high end horsepower. When mine broke and was stuck on the short runners, it was quite noticeably more sluggish on the bottom end.

[ForcedFirebird]

Here is my thoughts.. If there is ITB's vs. STB (Single Throttle Body) with the same runner lenght and size (comparing when itb setup doesnt contain "collector chamber", let's think it without it first) The main difference is getting more equal air flow to each cylinder. There is always problem if using STB manifold that you should make the manifold that way that every cylinder would have same amount of air. M20 has great intake manifold design for its age. I always think air flow : "Air has will to flow straight" if understand my opinion.

Cylinder 1 and 6 are ones which have The longest distance from TB. and the cylinder 3 and 4 have the shortest. I haven't measured the M20 intake manifold but I think they have little bit different size and lenght runners when comparing the middle ones with the ones on the corner.. But The order in chamber after TB makes also its part of flow. It is much easier way to flow into runners 1 and 6 at the back of the chamber than the runners at right after TB ( 3 and 4) thats because softer turn in air flow. However I have seen some Flow test that have been run to m20 manifold and it says there is no much difference between cylinders.

Second thought when comparin ITB and STB is the manifold design.. ITB has straight tunnel, which makes lower flow resistance than manifold that has bended runners like in stock manifold. But the bended runners may have other properties. They might make the right kind of turbulence which improves air flow at lower RPM. Also Chamber between runners and STB collects all in one and makes vacuum that improves air flow from low rpm to middle rpm.

ITB design to stock m20 885 head is pretty hard because the inlet ports. Everything should be smooth as possible. Check my ITB project that I'm running now...

Flow tested the stock m20 manifold/head before and they are nearly equal, throttle attached and plate locked open. BMW did a pretty good job.

[ForcedFirebird]

^

Yeh that is what I would of thought as well shorly someone has tested this though

Two people linked you to Rama's thread where he dynoed a bone stock m20 with mileage on it, then attached properly designed ITB's and it made more power. So, yes it WAS tested.

If ITB's didn't make more power, why would so many racing engines and the real Motorsport engines come with them? The problem lies in design. Most companies make a design that fit easy, or looks cool and don't really do any real research/testing.

[Massimo]

Two people linked you to Rama's thread where he dynoed a bone stock m20 with mileage on it, then attached properly designed ITB's and it made more power. So, yes it WAS tested.

If ITB's didn't make more power, why would so many racing engines and the real Motorsport engines come with them? The problem lies in design. Most companies make a design that fit easy, or looks cool and don't really do any real research/testing.

I don't think you are quite understanding what I am getting at here.
Yes ITB's generally will always make better power then a stock intake system.

I Want to know if you had an engine and two intake systems with exactly the same runner design and length and exactly the same plenum design and the only difference between the two systems is that one has a butterfly before the plenum and the other has a butterflys in each runner would there be any difference in peak power at full throttle?

As for race engines the reason for having them is the quicker response time not more power as I understand.

[ForcedFirebird]

AH! Totally misunderstood.

Here's a good article regarding runner length pre throttle plate...

http://www.emeraldm3d.com/articles/emr-adj-length-intake/

If the throttles were at the port entrance on a stock m20 manifold, based on this real world test, it believe it would be the "tractor" scenario.

[jute91]

Barry, it sounded nice, but to be honest the S14 sounds better with a carbon airbox. You could hear the difference too at the nurburgring, especially standing outside the corner Brunchen. Because there are more pulses in a 6cyl vs. a 4cyl, the noise is smoother and less boomy. The M3csl sounded cool, but a carbon airbox'd E30 M3 was always the coolest sounding car climbing up the hill.

My opinion? 6-cylinder might sound smoother with more pulses, but I think the main difference is compression ratio.. I have been following Finnish rallycross where there is lot of m/s54 engined e46's and couple m20 engined e30's. When you take the compression ratio up, there comes problems with engine knocking. But there is a way to prevent knocking by the shape of the compression chamber.. smoothen every edges so there wont be any heat peak in any edge. We use 12,5:1 compression ratio on our Ford pinto engines with pump gas. thin comp chamber with wide area to make mixture exploding in the chamber, not in cylinder.. that's how you prevent knocking..

But yeah you can make 6-cylinder engine sound as mad as 4-cylinder with high compression ratio and high rpm..

http://www.youtube.com/watch?v=7pd3v09Omkw

High rpm is easier with 4-valve head and you know why :)

[LJ851]

But yeah you can make 6-cylinder engine sound as mad as 4-cylinder with high compression ratio, a racy camshaft and high rpm..

Fixed

[jute91]

Fixed

Well done.

[digger]

the actual throttles in an ITB setup really can only help power by slightly more turbulence near the injector which sometimes helps fuel preparation which aids combustion efficiency.

otherwise its the straighter shot runners (better flow coefficient), hopefully correct length and diameter that provide the gains all of which can be done with a custom single throttle body intake and usually the case on a properly designed turbo intake manifold.

take a S54 with CSL CF airbox stick a whopping big single throttle at the start and get rid of the little ones and you will make pretty much same hp might be slight difference due to the shaft of the ITB providing a slightly higher resistance to flow.

if you use a smaller plenum than typically used on a I6 airbox (which is nothing more than a cold airbox on most) you can tune it to increase VE in small rpm band but outside of this you lose VE since it only works in a narrow band. with an inline 6 engine the volume is usually so small that it becomes difficult to get even distribution and equal length runners and fit under the hood. often OEM use a split plenum for this so that there are only 3 runners feeding each plenum as it maximises the effect

ITB help with tuning though with radical cams it helps alot and you can get a good tune with Alpha N

ITB and tunability and drive ability is markedly better you dont get so much cross talking between each runner as you do in a common plenum setup

[Massimo]

the actual throttles in an ITB setup really can only help power by slightly more turbulence near the injector which sometimes helps fuel preparation which aids combustion efficiency.

otherwise its the straighter shot runners (better flow coefficient), hopefully correct length and diameter that provide the gains all of which can be done with a custom single throttle body intake and usually the case on a properly designed turbo intake manifold.

take a S54 with CSL CF airbox stick a whopping big single throttle at the start and get rid of the little ones and you will make pretty much same hp might be slight difference due to the shaft of the ITB providing a slightly higher resistance to flow.

if you use a smaller plenum than typically used on a I6 airbox (which is nothing more than a cold airbox on most) you can tune it to increase VE in small rpm band but outside of this you lose VE since it only works in a narrow band. with an inline 6 engine the volume is usually so small that it becomes difficult to get even distribution and equal length runners and fit under the hood. often OEM use a split plenum for this so that there are only 3 runners feeding each plenum as it maximises the effect

ITB help with tuning though with radical cams it helps alot and you can get a good tune with Alpha N

ITB and tunability and drive ability is markedly better you dont get so much cross talking between each runner as you do in a common plenum setup

Thank you that was the kinda of answer I was looking for and with the detail I wanted.