Stock Midpipe too restrictive? - Subaru WRX Forum
 
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#1 Old 09-12-2008, 12:53 AM
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Stock Midpipe too restrictive?

As of right now I am thinking about doing a turbo upgrade but at the same time want to continue keeping the car as quiet as possible during normal driving. I have a catless up-pipe, catted bellmouth downpipe, stock midpipe, and the scoobysport axle back. When I do the upgrade will the stock midpipe hinder performance? I plan on going with an external wastegate as well when I do my turbo upgrade. Thanks.
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#2 Old 09-12-2008, 01:31 AM
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What downpipe do you have? 90% of em replace the midpipe as well as the downpipe.

The only exhaust restriction on your car was the wastegate merge right out of the turbo which is solved by the bellmouth. The rest of it is not a restriction.

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#3 Old 09-12-2008, 01:56 PM
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I have a catted bellmouth helix downpipe. However, I will be using a bracket to block off the internal wastegate flapper to run the external wastegate eventually.
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#4 Old 09-12-2008, 02:20 PM
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if you have a catted helix downpipe (I do as well), you do NOT have a stock midpipe.

The helix downpipe, like most aftermarket downpipes, replaces both the stock downpipe and midpipe with one longer piece of piping they call a downpipe.

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#5 Old 09-12-2008, 06:46 PM
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Okay I'm sorry. I meant rear exhaust pipe then. Is there any restriction on that pipe alone?

Last edited by mosc; 09-13-2008 at 01:32 AM.
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#6 Old 09-12-2008, 11:35 PM
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None with a stock turbo. PPL have proven it on a dyno removing it completely with zero gains.

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#7 Old 09-13-2008, 12:29 AM
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Well I'm going to upgrade the turbo soon to an EVO III 16g. So I'm not sure if it'll hold it back then, I know it doesn't really make a difference on a stock turbo obviously, but just checking if it was a bigger turbo. The reason I left the stock rear exhaust pipe is due to noise reduction and droning.
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#8 Old 09-13-2008, 01:33 AM
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It might cost 3whp or something with that turbo. It is 2.25" piping... If you like the sound, I'd leave it alone.

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#9 Old 09-13-2008, 05:12 PM
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Sounds good to me. Stealth is always better as long as the setback is minimal. Thanks.
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#10 Old 09-13-2008, 08:41 PM
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Not at all trying to discredit Mosc and his knowledge. He has helped me with questions also. But thought this might also help you some to understand and see that its not that big a deal CobbTuning.com - Exhaust Design

Joshua
"2007 WRX- PPG'd, 20G- Tim Bailey tuned
Stage 2 2005 WRX
Cobbtuning.com"
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#11 Old 09-20-2008, 12:38 AM
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Just make sure you don't have any exhaust leaks.

Terminology for the 2 "intermediate" pipes has never been and never will be clear. I have found that most people refer to the pre-muffler portion of the catback as the midpipe and the pipe with the 3rd cat, the catpipe so that is what I call them. Too bad the guy that made that diagram thought otherwise...
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