Exhaust system layout

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Thread: Exhaust system layout

  1. #1

    Exhaust system layout



    In case someone want to improve performance... and replace exhaust

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  3. #2
    Wastegate
    Join Date
    Sep 2000
    Location
    Mulbarton, was Deepest Mid Norfolk
    Posts
    8,948

    Re: Exhaust system layout

    That's horrendous!

  4. #3

    Re: Exhaust system layout

    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.

  5. #4
    Saab Afficionado
    Join Date
    Aug 2003
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    Southern California
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    1,448

    Re: Exhaust system layout

    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~

  6. #5

    Re: Exhaust system layout

    Adrian,

    Do you post on 'clubwrx.net' ?

  7. #6
    Saab Afficionado
    Join Date
    Aug 2003
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    Southern California
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    1,448

    Re: Exhaust system layout

    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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