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Old 04-03-2001, 03:46 PM   #1
Scooby Newbie
Member#: 4212
Join Date: Feb 2001
Location: Colorado Springs, CO, USA
2002 Impreza WRX

Post Newbie questions on upgrading WRX intake/exhaust...

Well, actually this question pertains to any car's intake/exhaust. How does a less restrictive exhaust or a better intake affect fuel economy? Will the ECU compensate for the greater volume of air by injecting more fuel?

Also, WRX specific, what kind of intake mods are most people planning on doing? So far all I've heard anyone say is they will put in a K/N filter and leave everything else as is, since it already has a system for cold-air intake. Would this car not benefit from a non-stock intake as much as another?

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Old 04-03-2001, 04:48 PM   #2
Scooby Specialist
Member#: 297
Join Date: Sep 1999
Location: Wa

I don't really know the answer to your first question but I think that the "fun factor" of the mod giving you more HP will mysteriously increase the weight of your right foot causing worse gas mileage!

The second one though. I would say the WRX will benefit from a LESS restrictive intake and exhaust. But the intake needs to pull cold air. I plan on doing an intake someday (when someone makes one) that pulls air from the fender. One bad thing is the airflow sensor is molded into the air filter box. Almost like Subaru didn't want us to put intakes on!

With a less restrictive exhaust the turbo will spool up faster. Maybe it would be best to leave the headers and up pipe to the turbo the stock size but increasing the down pipe and rest of the exhaust to 3" to reduce back pressure. The smaller exhaust before the turbo will increase exhaust velocity causing the turbo to spool faster.

Or I may be full of crap!
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Old 04-03-2001, 04:50 PM   #3
Member#: 456
Join Date: Oct 1999
Chapter/Region: NWIC
Location: Redmond, WA, USA
2008 Forester XT
Steel Gray Metallic


I think you want to leave everything from the panel filter back (MAF etc) as is. Panel filter is plenty large.

The snorkel/resonator thing in the fender and the cold air intake to it could perhaps use some work. I'd want a complete bolt in replacement though. ANother issue is water ingestion.

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Old 04-03-2001, 05:06 PM   #4
Scooby Specialist
Member#: 297
Join Date: Sep 1999
Location: Wa

True, true.... I haven't actually spent much time looking under the hood. I am to busy driving it. 650 miles in five days! I could have gotten 1000 if I tried though.

Well see what parts are made for the car and how they affect it. I don't plan on doing anything to it other than the gauges and tinting for a while anyways.
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Old 04-04-2001, 12:32 AM   #5
Scooby Specialist
Member#: 3792
Join Date: Jan 2001
2002 6MT almost GDB


I am going to go with the Apexi filter/ intake system from Japan. I have many many issues of Japan's famous 'Carboy' Magazine (Featuring some of the fastest cars in the world), and EVERY one of them has an aftermarket intake. There is a 350bhp ej20t in there with an apex one and they said that is one of the fastest Impreza's that they have driven to date. That does it for me. It was not a CAI either. I am also going to move the IC to the front of the car as I am going to be setting her up for road racing. I am going to use a BPM downpipe and midpipe with an HKS Hyper mufler (from the cat back). I am also going to use the latest HKS ball bearing turbo. This bad girl is going to haul my poor butt (after my mods) around. I also may stroke her to imitate the 22b. I am working toward my dream.
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