Subaru "boost tube"

From a theoretical view I expect that the extra volume would help when at relitively low turbo shaft RPM's going from closed throttle to open throttle. However the volume would also hurt when turbo rpm is incressing as it would take longer to build pressure, so they must figure the turbo spools up faster then the tank drops pressure. When we consider that turbos are producing something like 400 CFM or ~7 Cubic Feet per Second we can see even a very large tank would have very little time to be effective. It may also act to lessen the shock of closing the throttle quickly. As I see the tank basically dampins spikes in pressure, both positive and negative changes.

Air temp would be unchanged as we are not seeing a pressure drop in the tank, in fact having the tank lessens the pressure drop vs. a standard tube and thus lessens the temp drop: PV=NRT thus the more V the less T on the other side is going to go down. P=Pressure, V=Volume, N=Number of molecules, R=Universal Gas Constant, T= Temp. One of the more edumecated folks can follow up and correct all the errors that have accumulated in my head since I finished up college a few decades ago if I am wrong.

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In the long run reality always wins.

derek Wrote:
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> From a theoretical view I expect that the extra
> volume would help when at relitively low turbo
> shaft RPM's going from closed throttle to open
> throttle. However the volume would also hurt when
> turbo rpm is incressing as it would take longer to
> build pressure, so they must figure the turbo
> spools up faster then the tank drops pressure.
> When we consider that turbos are producing
> something like 400 CFM or ~7 Cubic Feet per Second
> we can see even a very large tank would have very
> little time to be effective. It may also act to
> lessen the shock of closing the throttle quickly.
> As I see the tank basically dampins spikes in
> pressure, both positive and negative changes.

From a practical point of view, I don't see that the increased volume is going to make enough of a difference with respect to response when the turbo isn't spinning. (For the most part, turbo speed mostly defines boost, not flow.) Adding four liters of volume is eight engine revolutions or so, at 1000rpm this is something like a half-second's worth of air and it's not like the volume needs to be fully discharged to allow pressurized air in, the air that's already in there will be pressurized so it matters even less. Plus, there's no appreciable difference in response when going from a top mounted intercooler to a front mount with 8-10 feet of additional ducting.

What I DO see however is a gread reduction of VELOCITY in front of the throttle body. How that is important, is the air in the tube will not have to accelerate as much when going from shut throttle to open throttle, or decelerate as much when you shut that throttle in the first place.

Neat setup...

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Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.

i heard it was an anti-reversion chamber, or that was the theory anyways....

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-Mark
www.nocoastmotorsports.net

They could be cleverly packaging a helmholtz resonator in an effort to boost some part of the powerband, but I suspect its actually what Pete suggested. Benefit should be a fraction of a second less lag after each upshift. Nice stuff.

-Dave

...i guess we'll soon find out...

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Chris

translated a Dutch site,
http://translate.google.com/translate?js=y&prev=_t&hl=en&ie=UTF-8&layout=1&eotf=1&u=http://www.extreme-machines.nl/forum/viewtopic.php%3Ft%3D42653%26sid%3D31ff6f8900aa7868d3e453d8baa173e9&sl=nl&tl=en

- there is a pressure reservoir that uses excess boost, and inserts it at low RPMs behind the throttle to increase/maintain boost.
or basically pre-pressurize the huge intercooler, and keep the turbine spinning.

another explanation from NASIOC -though the "rocket" turbine shit is ridiculous. clearly just a reservoir for compressed gas - no combustion there.
the large valve on the flex pipe of the exhaust manifold of the subuaru is pre-turbine, and there is clearly an external waste gate post turbine
so i'm guessing that it's where fuel is injected and ignited to spin up the turbo for the anti lag.

http://translate.googleusercontent.com/translate_c?hl=en&ie=UTF-8&sl=nl&tl=en&u=http://forums.nasioc.com/forums/showthread.php%3Ft%3D1650384&prev=_t&rurl=translate.google.com&twu=1&usg=ALkJrhhHr_DlSrm-DRvZKpt0KDldSgTaUA

watch this video and note the sound and RPM of the subarus




also clearly remember the mitsubishi WRC in car from 2007 having a click woosh sound.



at 15 seconds when the rpms drop and often afterwards. gardemeister driving.

Here is a Skoda WRC, look at the antilag blaster above the exhaust manifold, and how it gets the intake air from the pressure side of the intake.
http://forums.vwvortex.com/zerothread?id=4620769&postid=61613935

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"I put the hurt on dirt" - adam crane
http://CraneRallyCrew.com
corolla gt-s "Patches"
Op: S.S.



Edited 1 time(s). Last edit at 12/17/2009 11:32PM by acrane.

Silly people!

It's where the dilithium crystals are stored!

Duh!

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Nick Taylor.
Knobhead.
Los Angeles, CA.

so my friend just emailed me back:

"Re: technical question for you

"Yes it stores boost that's about all I can say." "



there you have it folks



I posted this same question over on dirtyimpreza.com and this is the best answer (that makes the most sense to me at least) I heard as well....

Quote

But the thing is, the volume DOES change. When the throttle plate closes, it severs the volume of the intake manifold from the intercooler and piping, creating two volumes. With the plate closed, the intake manifold goes to vacuum almost instantly. However, the turbo is still spinning. There are no brakes on the impeller, so it still has inertia to keep it spinning and making boost. Your boost gauge is reading the pressure of the intake manifold volume, not the piping before the throttle body.

So the intercooler and piping stays charged because the turbo is still spinning. Now, when you step back on the throttle, the high pressure air rushes in to fill the vacuum in the intake manifold. The pressure difference will equalize. The "lag" you see when going on and off throttle quickly is actually the turbo trying to repressurize, not spin up.

However, because volume and pressure are related in this situation, having less pressurized volume waiting to enter the intake means a lower average once equalized. Increasing the volume of the intake piping means a higher mean pressure once the two volumes are connected and equalized.

Now, this does increase the overall volume of the entire intake tract, which means it takes longer to pressurize. So this boost tube is really only for quick on/off/on throttle situations. But since there's no BOV/BPV, once pressurized, the intake piping before the throttlebody will tend to stay under pressure. The anti-lag system is beneficial because it will keep the turbo spinning and hence keep that piping pressurized, and to help initially charge the piping in the first place.

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Jon Burke - KI6LSW
Blog: http://psgrallywrx.blogspot.com/



Edited 1 time(s). Last edit at 12/20/2009 06:30PM by Jon Burke.

I guess another question, what's the pipe running from pre-intercooler to the turbo area? From Dave Colemans article on the X-Games Fiestas I would guess this is probably attached to the exhaust pre-turbo for the anti-lag system?

Its part of a very expensive anti-lag/pre-spool system. The tube dumps air into the exhaust (there's a valve controlling it somewhere down there), and the big cylinder sitting in front of the intake manifold is some kind of combustion chamber that feeds in fire. That's the word on the street, at least. Still trying to figure out how an aluminum tube has the structural wherewithal to be a combustion chamber, and I still don't see how its connected to the system, so probably that's all BS...

-Dave

The antilag system we ran for a short time in the hill climb Audi used a HKS bypass valve, dumped air directly into the exhaust manifold. Then super retard the timing so the spark hits when exhaust valves are fully open and BANG! Loudest and most violent antilag I've ever heard. The benefit was retaining engine braking as the spark was literally that late. Never really ran with it as it was seriously that violent. Like worried about breaking out the windows in the shop and it made it scary to go near it. If we had a turbo sponsor, maybe would have left it and went with it...

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Grant Hughes

NoCoast Wrote:
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> The antilag system we ran for a short time in the
> hill climb Audi used a HKS bypass valve, dumped
> air directly into the exhaust manifold. Then
> super retard the timing so the spark hits when
> exhaust valves are fully open and BANG! Loudest
> and most violent antilag I've ever heard.

http://www.bufkinengineering.com/Umluft.htm

I don't think we're looking at the same piece on the Subaru setup, though. There IS a device to dump charge air into the exhaust stream but the technical question (I thought) is, what's up with the huge diameter piping between the intercooler and throttle body?

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Pete Remner
Cleveland, Ohio

1984 RX-7 (rallycross thing)
1978
Silence is golden, but duct tape is silver.

Looking at the picture, that aluminum "combustion" chamber has a rubber hose (unless it's a stainless covered in rubber?) going to it from the turbo area. I've got a bunch of WRC Subaru engine bay pics that can give different angles. Let me get them uploaded... Pics are 2007, 2007, 2003-2005, 2006.

That reservoir looks like it's coming from the power steering on other generations of the engine bay.

http://forums.nasioc.com/forums/showthread.php?t=1650384&highlight=wrc+rocket

^^^ That other thing - not the boost tube.



Edited 1 time(s). Last edit at 12/23/2009 10:18AM by Daniel Buehler.

If that's the article Dave mentioned. I don't think there is combustion in that chamber, it just holds pressurized air in it? It's just a clever way of doing ALS with not so much BANG BANG.

Bit off topic, but new WRC cars more go "chirp chirp" but is that just due to the lack of a blow off valve and the noise is compressor surge?