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Old 08-26-2014, 10:29 PM   #1
Scooby Newbie
Member#: 39160
Join Date: Jul 2003
1993 Legacy RS

Default Stage 2 STI MY07, Is the stock muffler a restriction?


I just finished the remap for my MY07 STI Limited with pretty good numbers. This is the virtual dyno plot:

The red plot is the car with 3" downpipe, the blue plot is downpipe plus, Perrin EL headers, Perrin uppipe, Ebay turbo silicone inlet, ported VF43 exhaust housing, boost referenced water spray and torqued performance remap.

I'd like to keep the stock look of the car, including the engine. So I keep the stock airbox, midpipe and axle back.

The car is very fun to drive because of the midrange torque, but after 5000 RPM there is a huge decrease in both, power and torque. At this time I don't intend to change the turbo, but I donīt know if is possible to get some gains with other mods, by example:

- Is the stock muffler, midpipe and airbox a restriction for this level of power?
- Is necessary replace the STI Intercooler?
- Or, How can the top end power be increased without change the turbo?


Regards from Chile
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Last edited by Fredysan; 08-26-2014 at 10:35 PM.
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Old 08-26-2014, 11:00 PM   #2
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Prepare for a crash
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Old 08-26-2014, 11:18 PM   #3
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Member#: 120461
Join Date: Jul 2006
Chapter/Region: BAIC
Location: Bay Area/ L.A
2004 WRX STi JBP


well the stock exhaust is 2.5 inch, so without it you don't have a full 3" turboback exhaust, I'm sure it causes some kind of backpressure..
I asked my tuner if it would be okay to run my stage 2 protune (tuned on 3" turboback) with just the DP and a stock axleback, and he advised against it(and said it would change the parameters it had been tuned on)... hopefully someone else with some tuning experience can chime in on the actual effects.

As far as the intake, the general consensus is that you'd prolly only make maybe 5 more hp or less with an aftermarket intake, its not a real restriction until you upgrade the turbo.

just my 2 cents.
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Old 08-27-2014, 03:31 AM   #4
Uncle Scotty
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what ya want is a 'straight through' design muffler on the axle back...even a 2.5" one is just fine if it has a 'straight through' muffler

regardless of what all the kidiots think they know about exhaust
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Old 08-27-2014, 04:50 AM   #5
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7/2 STi/WRX wagon


You can realize modest gains with an aftermarket muffler but to see gains in the top end power you will have to change the turbo.
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Old 08-27-2014, 07:41 AM   #6
Medium Frank
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Join Date: Feb 2007
Chapter/Region: MAIC
Location: Common Sense, VA
2013 Audi
A6 3.0T


Short answer, no.
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Old 08-28-2014, 09:53 PM   #7
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1993 Legacy RS


Thanks for your answer!

I will stay with the stock muffler and airbox
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Old 08-29-2014, 01:48 AM   #8
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Join Date: Jun 2007
Chapter/Region: SCIC
Location: Irvine, CA
2014 STI


The stock air box is very efficient. Even though I'm running a cobb intake with the air box, it is still no where near as efficient as stock due to it being more prone to heat soak.

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Old 08-29-2014, 06:27 AM   #9
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2011 STI Stg2 w/EBCS
Focal 2way Active w/ DSP


Actually, there is evidence put there showing that a well designed intake does reduce pressure drop especially in high RPMs which means gains in top end. But, they are modest and will not drastically change your curve. On a stage2 car, intake side is the restriction. Your stock muffler may have some effect but it is very negligible. You could look at improving the overall the efficiency of your system by wrapping and isolating the hot parts: turbo wrap, downpipe wrap. Also, ELHs would improve efficiency but that would put a dent in your stealth strategy. Overall, sorry but you will not drastically change things without a turbo swap.

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