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Old 02-16-2006, 11:57 AM   #1
happasaiyan
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Default effects of varying intake pipe diameter? (pre and post turbo)

yesterday, i went to the chicago auto show, and had a chance to peek under the hood of the 2006 STI rally car. hoping to see if they had any tricks to squeezing out so much torque whilst using restrictor plates, i saw some interesting things.

its kind of hard to tell all the details from the picture, but there is a large black intake box, but then steps down to a smaller ID pipe which goes into the turbo. then, there is a pipe coming out of the turbo (charge pipe) that is roughly the same ID as an APS FMIC charge pipe. then, the piping coming out of the intercooler is what struck me- right after the intercooler (and the smallish piping), it immediately steps up to about a 4" ID pipe....when then steps back down right before entering the TB/intake manifold.

im definately not an enginner or anything of the sorts, but to me, it would seem this setup would actually create lag...since the air has already been cooled, and takes up less space, so putting it into a larger pipe would seem backwards to me.

im just wondering what you guys think, and if anyone has any ideas as to why they do this, and the theory behind it.



...maybe we can learn something from it.
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Old 02-16-2006, 12:10 PM   #2
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Quote:
Originally Posted by happasaiyan
yesterday, i went to the chicago auto show, and had a chance to peek under the hood of the 2006 STI rally car. hoping to see if they had any tricks to squeezing out so much torque whilst using restrictor plates, i saw some interesting things.

its kind of hard to tell all the details from the picture, but there is a large black intake box, but then steps down to a smaller ID pipe which goes into the turbo. then, there is a pipe coming out of the turbo (charge pipe) that is roughly the same ID as an APS FMIC charge pipe. then, the piping coming out of the intercooler is what struck me- right after the intercooler (and the smallish piping), it immediately steps up to about a 4" ID pipe....when then steps back down right before entering the TB/intake manifold.

im definately not an enginner or anything of the sorts, but to me, it would seem this setup would actually create lag...since the air has already been cooled, and takes up less space, so putting it into a larger pipe would seem backwards to me.

im just wondering what you guys think, and if anyone has any ideas as to why they do this, and the theory behind it.



...maybe we can learn something from it.

Someone like Hotrod or sponaugle would be better suited for this Q, but I'll take a redneck-stab at it:

Much like restrictor plates in NASCAR, they've found a way to "play with" the pressure and velocity of the pre/post-compressed air to help alleviate the effects of the restrictor. I.E. GP bikes. I imagine that the inside of the intake manifold and cylinder heads would be much more telling.

No answer, but I'd bet a wad no one's going to divulge that.

S.
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Old 02-16-2006, 12:13 PM   #3
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I'm wondering if the pipe inside that huge 4" section isn't actually the same diameter. Maybe that's just a large pipe with an airspace to insulate the cool air out of the intercooler so it doesn't get heated by the engine bay heat.

Maybe it is just the picture, but the pipe from the turbo to the intercooler looks TINY. Like 1.75" or something.
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Old 02-16-2006, 12:15 PM   #4
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hmm, maybe a custom setup could duplicate that intercooler position.... it's just as spiffy as a v-mount
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Old 02-16-2006, 12:15 PM   #5
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Default

Quote:
Originally Posted by n2xlr8n
Someone like Hotrod or sponaugle would be better suited for this Q, but I'll take a redneck-stab at it:

Much like restrictor plates in NASCAR, they've found a way to "play with" the pressure and velocity of the pre/post-compressed air to help alleviate the effects of the restrictor. I.E. GP bikes. I imagine that the inside of the intake manifold and cylinder heads would be much more telling.

No answer, but I'd bet a wad no one's going to divulge that.

S.
yeah, i bet no one involved will divulge the findings...

...but we have a few intelligent people on these boards that may know the theory behind it...

...darn, steve, i thought you wouldve been one of them
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Old 02-16-2006, 12:17 PM   #6
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Default

Quote:
Originally Posted by Freon
I'm wondering if the pipe inside that huge 4" section isn't actually the same diameter. Maybe that's just a large pipe with an airspace to insulate the cool air out of the intercooler so it doesn't get heated by the engine bay heat.

Maybe it is just the picture, but the pipe from the turbo to the intercooler looks TINY. Like 1.75" or something.
thats actually a separate pipe. the charge pipe runs underneath the intake piping. the piping you are talking about goes somewhere else...i couldnt get close enough to take a picture that would show it.
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Old 02-16-2006, 12:23 PM   #7
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Quote:
I'm wondering if the pipe inside that huge 4" section isn't actually the same diameter. Maybe that's just a large pipe with an airspace to insulate the cool air out of the intercooler so it doesn't get heated by the engine bay heat.
ding ding ding... I would be willing to bet the same thing. Its gotta either be airspace that is insulated to lessen heat OR its a water cooled jacket and there are lines going in/out that we can't see as well.
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Old 02-16-2006, 12:27 PM   #8
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Quote:
Originally Posted by happasaiyan


...maybe we can learn something from it.
Seeing that pic, makes the new front end make sense.
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Old 02-16-2006, 12:29 PM   #9
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Quote:
Originally Posted by happasaiyan
yeah, i bet no one involved will divulge the findings...

...but we have a few intelligent people on these boards that may know the theory behind it...

...darn, steve, i thought you wouldve been one of them

Sorry to disappoint, but I know my place. No doubt there are several that could make good guesses, but I'm not one of them

Seriously. Not to go off-topic, but taking a look at some of the radical exhausts on the new GP bikes....it gets one thinking: New Science?

S.
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Old 02-16-2006, 12:42 PM   #10
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I will comment that if it is intended to insulate, it makes no sense for it to be welded to the main inner pipe on both sides, nor to be made from aluminum. It looks like aluminum to me, and it is welded right as it goes from ~2.5" to 4".

Another theory is there are directional baffles or louvers inside to keep the air from reverting on shifts, and keep air in the system rather than dump it. On off throttle, air would try to travel back out through the pipe, but the louvers would direct it to the larger 4" diameter section.

Where is the BOV located?

Edit: I would definitely rule out that it is a big empty 4" pipe, with instant perpendicular transition from 2.5" to 4". No way...
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Old 02-16-2006, 12:49 PM   #11
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Default

Quote:
Originally Posted by Freon
I will comment that if it is intended to insulate, it makes no sense for it to be welded to the main inner pipe on both sides, nor to be made from aluminum. It looks like aluminum to me, and it is welded right as it goes from ~2.5" to 4".

Another theory is there are directional baffles or louvers inside to keep the air from reverting on shifts, and keep air in the system rather than dump it. On off throttle, air would try to travel back out through the pipe, but the louvers would direct it to the larger 4" diameter section.

Where is the BOV located?

Edit: I would definitely rule out that it is a big empty 4" pipe, with instant perpendicular transition from 2.5" to 4". No way...
i dont know where the BOV is located (i am just guessing, but that small pipe pre-intercooler might be it).

...here is a very high quality pic if anyone is interested

http://www.jasonyokoyama.com/pics/20...q/IMG_1505.jpg
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Old 02-16-2006, 12:51 PM   #12
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Default

Quote:
Originally Posted by n2xlr8n
Sorry to disappoint, but I know my place. No doubt there are several that could make good guesses, but I'm not one of them

Seriously. Not to go off-topic, but taking a look at some of the radical exhausts on the new GP bikes....it gets one thinking: New Science?

S.
any direct links to the GP stuff?
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Old 02-16-2006, 12:54 PM   #13
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Quote:
Originally Posted by n2xlr8n
Sorry to disappoint, but I know my place. No doubt there are several that could make good guesses, but I'm not one of them

Seriously. Not to go off-topic, but taking a look at some of the radical exhausts on the new GP bikes....it gets one thinking: New Science?

S.
those types of exhausts only work on 2 stroke motors (at least that is my guess) because i never see them on anything else.

edit more data on expansion chambers:
http://en.wikipedia.org/wiki/Expansion_chamber


I'd say it's safe to say we can exclude the expansion chamber theory.

Last edited by AaronWRX; 02-16-2006 at 01:03 PM.
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Old 02-16-2006, 01:13 PM   #14
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I would bet the intercooler outlet pipe utilizes a liquid to air design which makes sense considering the intercooler is laying relatively flat for aerodynamic purposes but has drawbacks in regards to cooling efficiency.

TR
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Old 02-16-2006, 01:24 PM   #15
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Quote:
Originally Posted by AaronWRX
those types of exhausts only work on 2 stroke motors (at least that is my guess) because i never see them on anything else.

edit more data on expansion chambers:
http://en.wikipedia.org/wiki/Expansion_chamber


I'd say it's safe to say we can exclude the expansion chamber theory.

That seems to be the general consensus, as it's what I believed, too.

Recently, I've read otherwise. I'll see if I can find it.

S.
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Old 02-16-2006, 01:29 PM   #16
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Quote:
Originally Posted by Thomas Ruble
I would bet the intercooler outlet pipe utilizes a liquid to air design which makes sense considering the intercooler is laying relatively flat for aerodynamic purposes but has drawbacks in regards to cooling efficiency.

TR
the lower air dam pushes the air up through the intercooler and out through the hood.
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Old 02-16-2006, 01:42 PM   #17
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Quote:
Originally Posted by happasaiyan
the lower air dam pushes the air up through the intercooler and out through the hood.
Yes I understand that but it is still not as efficient as air hitting the IC at a more vertical angle in front of the motor, not to mention the increase of heat soak potential.
I have NO idea what the WRC rule book says about the addition of liquid to air heat extraction but as I said earlier their are definite trade offs with positioning the intercooler as it sits now despite the attempts at redirecting air towards the intercooler. The engine compartmant sees alot of uncontrollable air tubulence.

TR
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Old 02-16-2006, 02:45 PM   #18
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Quote:
Originally Posted by Thomas Ruble
Yes I understand that but it is still not as efficient as air hitting the IC at a more vertical angle in front of the motor, not to mention the increase of heat soak potential.
I think that it is important to consider more that just the IC efficiency for a racecar. Those cars don't sit around for very long, so heat soak is likely not much of a concern for them, not nearly as much as aerodynamic drag is. It's also important that these guys are going to calculate just how much airflow they need to get certain intake temps and will design their airflow to match that. More airflow through the IC may not give them enough benefit to offset the increased drag.

Additionally, that positioning is possibly more tolerant to impacts with snow embankments as well as resistant to stone impacts. Having an IC out front ready to get hit by a large stone probably isn't the best idea from a reliability standpoint.
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Old 02-16-2006, 03:42 PM   #19
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Quote:
Originally Posted by todd_fuller
I think that it is important to consider more that just the IC efficiency for a racecar. Those cars don't sit around for very long, so heat soak is likely not much of a concern for them, not nearly as much as aerodynamic drag is. It's also important that these guys are going to calculate just how much airflow they need to get certain intake temps and will design their airflow to match that. More airflow through the IC may not give them enough benefit to offset the increased drag.

Additionally, that positioning is possibly more tolerant to impacts with snow embankments as well as resistant to stone impacts. Having an IC out front ready to get hit by a large stone probably isn't the best idea from a reliability standpoint.
I am familiar with race cars and the effects of heat soak, having a track car background. Heat soak from retained heat under the hood still occurs to some degree despite the car being in motion, it's just that the amount of heat absorbtion will be less when moving which is why a race engine ( a well built motor anyways ) will often times use ceramic coatings on various underhood components to both retain and or reduce heat absorbtion. Ceramic coating not only helps with EGV but also overall engine temps and potential power.

I don't really want to debate the effects of heat soak, my main point was intercooler efficiency with an air to air intercooler which depends on air flow to help dissapate heat away from the intake charge. Having an intercooler positioned nearly horizontal must have it's drawbacks in regards to overall efficiency hence the assumption, albeit maybe the wrong assumption that they are using a liquid to air pipe to compensate.



TR

Last edited by Thomas Ruble; 02-16-2006 at 04:52 PM.
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Old 02-16-2006, 04:02 PM   #20
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I don't understand that smaller pipe coming off the charge pipe right before the IC.

BTW, it appears the IC is tube and fin... <hijack time>
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Old 02-16-2006, 11:23 PM   #21
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Quote:
Originally Posted by Freon
I will comment that if it is intended to insulate, it makes no sense for it to be welded to the main inner pipe on both sides, nor to be made from aluminum. It looks like aluminum to me, and it is welded right as it goes from ~2.5" to 4".

Another theory is there are directional baffles or louvers inside to keep the air from reverting on shifts, and keep air in the system rather than dump it. On off throttle, air would try to travel back out through the pipe, but the louvers would direct it to the larger 4" diameter section.

Where is the BOV located?

Edit: I would definitely rule out that it is a big empty 4" pipe, with instant perpendicular transition from 2.5" to 4". No way...
As for it being water cooled around the pipe... I don't see any water lines, but then again they could always be underneath and out of view...

I think there is a good chance this is a directional baffle like you say. Something to help decrease lag after shifts occur. As the air shoots back toward the IC, it slams into (for the most part) the much, much wider piping and wall where there is transition from 3" pipe all the sudden to about 6-7" pipe. Louvers could be used to make the air flow fine on the way in, but get all broken up/slowed down on the way back... Only to be available to quickly get sucked back toward the intake mani after the shift is over...

EDIT: Or maybe I'm way the hell off...

Last edited by SilverSurfer04STi; 02-16-2006 at 11:29 PM.
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Old 02-17-2006, 01:58 AM   #22
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Quote:
Originally Posted by happasaiyan
i dont know where the BOV is located (i am just guessing, but that small pipe pre-intercooler might be it).

...here is a very high quality pic if anyone is interested

http://www.jasonyokoyama.com/pics/20...q/IMG_1505.jpg

I wouldnt think that the WRC cars would run a BOV, as its not really needed for their application. They also change turbos after every race thus having no BOV wont be a player in the fatigue of engine parts
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Old 02-17-2006, 03:18 AM   #23
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my theory:
looks to me like the very small pipe you see is joining onto the pre intercooler piping at right angles.... (check carefully the high res picture)
maybe this is pipe is used for anti-lag or something (feed oxygen rich air to the turbine and inject raw fuel which is ignited, when you close throttle airflow ceases to the hot side... but providing burning air/fuel keeps turbo at full power)
This would also mean they do not need a BOV.... because it works just like one just in a different way to our stret driven vehicle
It would make more sense to use the hot compressor air as they need heat to drive the turbine they would not require more dense (oxygen rich) air by using it from the cold side...

the very large pipe on the intercooler cold side is interesting
As for heat insulation I think there would be far easier and lighter ways to prevent heat soak into the pipe...
common sense would tell me that the entering pipe continues inside at the same dimension unimpeeded (the square edge on either end would be totally detrimental to air flow if it was an open cavity

maybe there is insulation inside and a perforated wall (somewhat like a flow through tube muffler)
this could have the effect of reducing unwanted intake pulsing (pressure waves).... that external aluminium pipe looks like it is built to take pressure and someone has gone to a lot of trouble to manufacture it ,not to mention the added weight of the welded aluminium piping...
whatever its purpose it must be well worth it you can bet on it
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Old 02-17-2006, 05:16 AM   #24
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the piping post intercooler is for odd resonant tuning for throttle response and torque.

lol iono thats something AEM would say for there CAI
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Old 02-17-2006, 05:28 AM   #25
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Not being able to crawl over and around it I can't totally dismiss the idea of a cooled jacket but I doubt it pretty strongly.

I'm pretty certain that there is a high likelyhood that there is some insulation function there, but one other possibility comes to mind. It could be functioning as a plenum, with a check valve at the inlet to hold a large reserve of pressurized air available to the manifold, and or eliminate or reduce the amount of mixture blown off by BOV on throttle closure. It along with antilag would hold a near constant supply of high boost pressure air immediately available on throttle tip in.

At least that is my guess.

Larry
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