downpipe/exhaust question
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This is a discussion on downpipe/exhaust question within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; I'm sure this has been asked before but fuggit I'm going to ask again. I have an 06 rex. I ...

  1. #1
    Roz
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    downpipe/exhaust question

    I'm sure this has been asked before but fuggit I'm going to ask again. I have an 06 rex. I was looking under the hood today trying to get more acclimated with the exhaust setup. Is this set up possible or is this how it is done:catless dp, hi flow cat, then cat back exhaust? Or would it be better to get a catted dp, cat, then catback? Thanks peeps!

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    Registered User TurnWRX's Avatar
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    for your 2nd option, why would u want 2 cats still if going with aftermarket parts? The whole point of exchanging exhausts is to free up more power and let the engine breathe easier. Now if you still want a cat in there for the environmental side in you, u can get a catted downpipe and then catback. Most downpipes replace the stock downpipe and midpipe, unless u get a shorty one.

    For your 1st option, you would basically be getting a shorty dp, a catted midpipe, and then catback.

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    Roz
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    there's no way I could go catless because I would never pass the sniff test here in upstate ny...is there a way to unly run one cat...and if I did would that be on the dp?

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    Registered User LeeC's Avatar
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    Your exhaust in most situations will be a Downpipe>Midpipe>Axle back, unless you have a shorty DP like in the TXS stealthback then you will have another short pipe between the downpipe and mid pipe. Stock the downpipe and mid pipe have cats, if you get rid of any cat, you would be better off getting rid of the one in the downpipe and leaving the cat on the midpipe or getting a high flow cat. I am not familiar with the 06 boost creep issue, I have heard about some people buying catted DP's to help this problem, I'm sure someone with an 06 could give you better info on which cat to keep.

    Lee
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    Registered User Newera09's Avatar
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    Quote Originally Posted by LeeC


    Your exhaust in most situations will be a Downpipe>Midpipe>Axle back, unless you have a shorty DP like in the TXS stealthback then you will have another short pipe between the downpipe and mid pipe. Stock the downpipe and mid pipe have cats, if you get rid of any cat, you would be better off getting rid of the one in the downpipe and leaving the cat on the midpipe or getting a high flow cat. I am not familiar with the 06 boost creep issue, I have heard about some people buying catted DP's to help this problem, I'm sure someone with an 06 could give you better info on which cat to keep.

    Lee
    the posting of the diagram of the exhaust set-up is one of the most helpful diagrams I have seen and I think it should be stickied by itself. It just answered about 4-5 questions that I had. thanks dooods
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    yep..kudos..that diagram is awesome, never seen it before. Simplifies a lot of stuff without poking around my engine bay (and i'm usually doing that while the engine is hot!).


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    Registered User rr1911's Avatar
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    Replacing the exhaust system on your 02-06+ WRX or STi is a great way to make power. Unfortunately, there is a lot of misinformation out there, and the exhaust system is composed of many different components. JSC speed has developed this informative guide, titled 'Exhaust 101' as a means of providing correct information and simplifying WRX exhausts using visuals and summarized information.

    NOTES ON CATLESS DOWNPIPES:
    02-05 WRX OWNERS READ: On the 02-05 WRX there are no boost spike or creep issues in most cases with the use of an aftermarket downpipe or turboback.

    06+ WRX OWNERS READ: On the 06+ WRX there are boost spike or creep issues in all cases with the use of an aftermarket downpipe or turboback. This is because the 2.5L engine pushes so much air. Even with the internal wastegate fully open not enough air can exit to stop spinning the turbo, the result is boost creep or boost spike. With the 06+ WRX, unlike the STi, you cannot fix the problem by just porting the stock turbo wastegate. We suggest porting the stock turbo wastegate AND getting an engine management system to help fix the issue like a UTEC or AccessPORT. With the added costs this will entail 06+ WRX owners may want to consider waiting to get an aftermarket downpipe or turboback after they have upgraded there turbochargers or they may want to consider getting a cat-back exhaust only.

    04-06 STi OWNERS READ: On the 04-06 STi there are boost spike or creep issues in all cases with the use of an aftermarket downpipe or turboback that uses a bellmouth or external dump tube design. This is because the 2.5L engine pushes so much air. Even with the internal wastegate fully open not enough air can exit to stop spinning the turbo, the result is boost creep or boost spike. You can fix the problem by porting the stock turbo's wastegate passage (any exhaust shop should be able to do this or it can be done at home) or you can get an engine management system to fix the issue, like a UTEC or AccessPORT.
    Last edited by rr1911; 11-19-2006 at 03:00 AM.

  9. #8
    Registered User rr1911's Avatar
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    got this stuff from jscspeed.com

    hope it helps
    Last edited by rr1911; 11-19-2006 at 03:00 AM.

  10. #9
    Registered User Robert46123's Avatar
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    Quote Originally Posted by rr1911
    06+ WRX OWNERS READ: On the 06+ WRX there are boost spike or creep issues in all cases with the use of an aftermarket downpipe or turboback. This is because the 2.5L engine pushes so much air. Even with the internal wastegate fully open not enough air can exit to stop spinning the turbo, the result is boost creep or boost spike. With the 06+ WRX, unlike the STi, you cannot fix the problem by just porting the stock turbo wastegate. We suggest porting the stock turbo wastegate AND getting an engine management system to help fix the issue like a UTEC or AccessPORT. With the added costs this will entail 06+ WRX owners may want to consider waiting to get an aftermarket downpipe or turboback after they have upgraded there turbochargers or they may want to consider getting a cat-back exhaust only.
    I'm thinking about going the opposite route for my '06 and going with a catless downpipe but leaving my stock cat back with resonator to avoid boost creep. It'd be stealthy and hopefully avoid boost creep. Any thoughts? TIA
    2006 WRX WRB Wagon
    Stage 2 Cobb catless DP and Borla Hush CBE
    *Total Loss*

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    Registered User DeBlas66's Avatar
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    That diagram has been around for a while. It is a GREAT diagram but 06 owners remember that the CAT in the uppipe is not there anymore and instead there are 2 in the downpipe.

    To the OP: These cars don't have to pass sniffer tests because of the AWD. As long as you don't have any CELs you should be fine. You also don't have to go for inspection for 2 years since the car is an 06. Even if you did have to pass a sniffer it would take you less than an hour to swap the stock downpipe back in for that day in 2 years from now.
    Car-less

  12. #11
    Registered User Robert46123's Avatar
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    Quote Originally Posted by DeBlas66
    That diagram has been around for a while. It is a GREAT diagram but 06 owners remember that the CAT in the uppipe is not there anymore and instead there are 2 in the downpipe.

    To the OP: These cars don't have to pass sniffer tests because of the AWD. As long as you don't have any CELs you should be fine. You also don't have to go for inspection for 2 years since the car is an 06. Even if you did have to pass a sniffer it would take you less than an hour to swap the stock downpipe back in for that day in 2 years from now.
    We don't have emmisions testing in Indiana (Lucky Me), and my main concern is boost creep. Anyone running the stock CBE with a catless downpipe on an '06? Any information is appreciated.
    2006 WRX WRB Wagon
    Stage 2 Cobb catless DP and Borla Hush CBE
    *Total Loss*

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    Registered User soon2BWRXd's Avatar
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    Quote Originally Posted by Roz
    there's no way I could go catless because I would never pass the sniff test here in upstate ny...is there a way to unly run one cat...and if I did would that be on the dp?
    Sniff test in Syracuse????????? Did I miss something? there is no sniff test here in Upstate NY, all they do is hook up an OBD-II scanner to look for CELs (direct link to NYS DMV)...if you have No CELs then you will pass. However you do need to have a cat to pass the visual inspection, but there are always ways around that!
    Stock or something close to it.....

  14. #13
    Registered User Robert46123's Avatar
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    Quote Originally Posted by Robert46123
    We don't have emmisions testing in Indiana (Lucky Me), and my main concern is boost creep. Anyone running the stock CBE with a catless downpipe on an '06? Any information is appreciated.
    No one is running this setup with an '06.? I've got to believe that the stock CBE including resonator will produce enough back pressure to eliminate boost creep. I'm not so concerned with the performance negative of the stock CBE as I think it's minimal at +/- 10 HP. Opinions are welcomed even if you're not running it. I've got a catless downpipe coming and AP stage one installed already. Let me know what you think. Thanks.
    2006 WRX WRB Wagon
    Stage 2 Cobb catless DP and Borla Hush CBE
    *Total Loss*

  15. #14
    Registered User soon2BWRXd's Avatar
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    Quote Originally Posted by Robert46123
    No one is running this setup with an '06.? I've got to believe that the stock CBE including resonator will produce enough back pressure to eliminate boost creep. I'm not so concerned with the performance negative of the stock CBE as I think it's minimal at +/- 10 HP. Opinions are welcomed even if you're not running it. I've got a catless downpipe coming and AP stage one installed already. Let me know what you think. Thanks.
    You can replace the stock CBE without a problem!
    Its elimination of the stock downpipe with it's VERY restrictive 2 cats that causes problems on the 06+.

    Now when you install the Catless DP you MAY see some boost creep(from what I read) but the Cobb AP should help to eliminate any problems. And if you get worried while you have your DP off pull the turbo and port the wastegate...this also helps reduce boost creep.
    Stock or something close to it.....

  16. #15
    Registered User ktmrider's Avatar
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    FNA that diagram is the bomb! Already copied it to my HD, thanks again.
    I thought the front O2 was in the up pipe, saved me some headaches for later.
    2005 Legacy GT - stock for now
    1991 Galant VR4 - Sold
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