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Actually not dissimilar to the current 9-3 and 9-5 (and many other modern cars).

The only major differences are that it's a flat 4 engine hence separate manifolds and there is an additional catalytic converter. The pre-cat is almost certainly a particle filter.

The additional complexity is almost all due to emissions control regulations.
 

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The pre-cat is almost certainly a particle filter.

More like a particle generator. More than one pre-cat has melted and destroyed the turbo on those cars. Generally though, it was because of a tuned ECU and low octane. (The IAM was really low so EGT was high.) Nevertheless, it's a dangerous place to put a catalyst and does measurably slow spool up.

Interestingly, despite slowing spool-up significantly, the UP catalyst doesn't cause too much backpressure once under load; removing that catalyst will lower EGT by about 50*F at the exhaust ports, whereas a full TBE will lower it an additional 150*F.


For those upgrading their exhaust, here are a few terms that might be usefull:

- Long downpipe versus short downpipe. Long dowpipe also replaces the midpipe shown in that image. Short downpipe doesn't.

- Axle back exhausts don't replace the midpipe or the resonator, but only the muffler. Catbacks replace the resonator and the muffler, but not the midpipe. A turbo back exhaust, obviously, replaces everything after the turbo.

Some other things to note are that the STi does not have a catalyst in the up-pipe, so it can be used in lieu of your stock pipe. Also, the up-pipe catalyst is very hard to see; most dealer technicians will notice its removal, but, suprisingly, many emission techs don't because it's so hard to see underneath all the heat-shields.

Also, it's a very bad idea to use an intake on a stock EJ20. The stock air-box is capable of well over 300 hp without incuring any significant pressure drop at the turbo. And, because the sensor merely attaches into the pipe, and is not a pipe of its own, most intakes change the sensor readings significantly and require engine management and a custom tune to use properly.

Also, it's advisable to get your 9-2X ECU tuned before getting an exhaust. As of 2005 the EPA drive cycle for these cars stipulates a certain amount of time spent at a stoich A/F ratio and closed loop. In some cases the ECU won't switch to open loop until 5,300 RPM which can cause audible knocking. A turbo-back exhaust system has been repeatedly shown to exacerbate this effect.

Just some food for thought I suppose.

Adrian~
 

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Originally posted by McScooby:
[qb]Adrian,

Do you post on 'clubwrx.net' ? [/qb][/b]
I have once for a friend, but only once. Generally I post on NASIOC and WRX Fanatics; at the latter of those two I'm an admin. At NASIOC I'm "SaabTuner" and at WRXF I'm "Thunderbolt".

The Subaru forums often have a lot of really in-depth technical discussions in which the tuners themselves regularly participate. Needless to say I was hooked quickly.

Adrian~
 
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