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Old 11-30-2008, 03:40 PM   #1
Bonjo2
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Default RallyAmerica Turbo Inlet and other Bits

Spent some time looking at the RallyAmerica and Subaru USA team site.. Wow, the usa thing is taking off--literally.

Can someone explain the mammouth sized turbo plumbing, esp the section prior from the I/C to the TB. Are most of the bits on the open cars now one-offs? The exhaust and intercooler setup something I think norms like us could benefit from--maybe in ST classes? Maybe some beefy susp arms now that everyone is trying to jump their subarus over mountains..

Happy Day. Thanks in advance.
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Old 12-01-2008, 02:26 PM   #2
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http://rally.subaru.com/event_2008_lspr_gallery1.html

The photo in question is about 1/2 way down. One reply mentioned it being either a water cooler like some supercharged cars run, another theory is it is in some way part of the antilag. Anyone know for sure?
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Old 12-01-2008, 02:57 PM   #3
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Looks like insulation to me.

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Old 12-01-2008, 03:21 PM   #4
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I''ve seen this on mulitple WRC cars over the past 3 years. I never really asked or looked into it. They all seem to have that sized piping coming off the IC to TB.

Here's a shot of the '07 engine bay with the intake where the stock IC goes.



more of the '06 setup



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Old 12-01-2008, 05:28 PM   #5
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Not insulation, but a type of expansion chamber. Unsure of the physics/dynamics of it, but it may have to do with holding a large pressurized volume of air....instead of sucking through a straw with a ball inflation needle at the end, you get more "straw" volume, making the best of what is available? I dunno...that is my layman response. I know that they make expansion pipes like that for my wife's Saab turbo
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Old 12-01-2008, 10:18 PM   #6
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that sorta makes sense assuming they keep it pressurized with the ALS, it could keep pressure and allow super quick throttle response when back on the go button. But like you, layman's guess

Thanks for the better photos.
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Old 12-01-2008, 10:24 PM   #7
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What doesn't make sense to me is the sudden change in diameter as there is a loss (quantified by "k" in most fluid dynamics books) that results from sudden changes like that. Not only would the velocity slow because of the V1A1=V2A2 (regainable energy if A2 returns to being small) but the expansion losses.

I like bonjo's explanation of the overall system (or at least his guess of it, as it makes sense to me). If the system is always kept pressurized (or at least at 0 vacuum) then when you get on the throttle, you don't need to build boost from negative pressure or fill up a large volume first. By the time the turbo has fully spooled, you've ben able to pull from the reserve resevoir to get the first response.

The volume might also be tuned a bit to the dynamics of the turbo/engine.
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Old 12-01-2008, 11:10 PM   #8
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Remember, those engines have to breath through a 34mm restrictor. I don't know how the "big pipe" quite works, but they may be saving up pressureized air on corner entry, closed throttle (CT), and getting a bit of an extra boost on corner exit, WOT. Just a theory on my part.
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Old 12-02-2008, 10:24 AM   #9
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send Rodney over at subaruwrcspares.com an email. We were looking at an ALS setup here at my shop that the wrc team uses. We though they were pulling air in through the intercooler...then up through the uppipe to keep the turbo spooling. Totally different system than the bang-bang ALS. Anyway's he sent me a very detailed response on how the subaru wrc ALS works with pictures and pricing. very informative.
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Old 12-02-2008, 10:28 AM   #10
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Quote:
Originally Posted by LukeD View Post
Anyway's he sent me a very detailed response on how the subaru wrc ALS works with pictures and pricing. very informative.
Please make a thread about this if you get a chance. The prodrive factory thread had some pics/info about this, but not much. You can definitely see the air bypass for the ALS on the hot side of the IC.
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Old 12-02-2008, 01:04 PM   #11
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Looks like it just increases the plenum, though I only really paid attention to the need for it back with the 98-01 RSs.
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Old 12-02-2008, 05:38 PM   #12
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Makes sense. A few manufacturers are putting variable-length intake manifolds on production cars - Porsche comes to mind. The idea is that for high rpm and WOT conditions, you want a short as path as possible to the intake. For lower throttle/rpm conditions, having a longer path provides a greater overall volume of air "in reserve" in case you suddenly go WOT and need the air. Improves throttle response and low-end torque if you believe the marketing folks.

I'm guessing that the larger intake tubing basically provides the extra air necessary when going WOT.
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Old 12-02-2008, 05:57 PM   #13
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has anyone seen the inside of these pipes? maybe they're hiding something...
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Old 12-02-2008, 06:06 PM   #14
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Quote:
Originally Posted by yarrgh View Post
has anyone seen the inside of these pipes? maybe they're hiding something...
I like it. Would be a great way to cheat. "Yea, we totally use that giant thing as an expansion chamber. There totally is not NOS in there, no way"

-Tom
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Old 12-02-2008, 06:26 PM   #15
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My guess is that the chamber acts like another plenum...so when a driver goes off throttle into a corner and punches the gas...the chambers stores extra air for a faster transition back into the power band.

Similar to a throttle body spacer which adds volume to the intake plenum.

To be honest...at speed the air is moving so fast through those pipes that the change in size probably has little effect, or is out weighed by the extra benefit of the larger chamber
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Old 12-02-2008, 06:27 PM   #16
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Old 12-02-2008, 08:17 PM   #17
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Very cool link.
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Old 12-05-2008, 05:24 AM   #18
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Awesome stuff. Thanks.
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