WRX uppipe, downpipe, exhaust questions.
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This is a discussion on WRX uppipe, downpipe, exhaust questions. within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; Hey guys, I just got an 05 WRX wagon, and had some questions about exhaust upgrades. I did search and ...

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    WRX uppipe, downpipe, exhaust questions.

    Hey guys, I just got an 05 WRX wagon, and had some questions about exhaust upgrades. I did search and read the FAQ's but nothing seemed to answer these specific questions. For now I want to keep the stock catback, maybe stock midpipe, maybe with an STI axle back, and want to replace the uppipe, and maybe the downpipe. I want to keep ONE working cat converter in the exhaust system.

    For the uppipe, would it be best to gut the stock cat in the stock WRX uppipe, buy a stock catless STI uppipe, or buy and aftermarket catless uppipe?

    Since I want to keep ONE working cat in the exhaust, and keep the stock WRX/STI catback, should I gut the stock cat in the stock WRX down pipe and keep the rear cat in the stock midpipe, buy an aftermaket catless downpipe and keep the stock rear cat in the stock midpipe, or buy an aftermarket downpipe WITH cat converter and remove the rear cat in the stock midpipe? (Which cat should I leave since I want to keep one there?)

    Lastly, is the stock WRX and stock STI midpipe/rear section the exact same other than the axleback/muffler?

    Thanks guys!

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    Registered User Terminal Kuz's Avatar
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    If you want to keep one cat, get a catted downpipes and go with a castles uppipe. Its up to you if you want to replace the uppipe or gut it. I bought a new one, and the downpipe will replace the midpipe probably like 90% of the time.

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    Master Baiter EJ257's Avatar
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    For the uppipe, it's your call. If it were me, it would be a choice between gutting the stock cat and buying an aftermarket unit. You can gut the cat for "free" (given the right tools), and won't really lose all that much vs going with an aftermarket unit, which can be had for ~$150 new. Either option requires the same gasket purchases, so your choice as to your time.

    If you're going to gut the stock cat, you need to be 110% sure you get all the catalyst material out, or else you did more harm than good, and will make it easier for a piece to break apart and get sucked into the turbo. If you can be thorough and make sure it's clean in there, there's nothing really wrong with gutting vs buying aftermarket. Saving the money with a used OE 2.5L uppipe just isn't worth it (IMO) compared to buying a used quality aftermarket one.

    If you want to gut the stock unit, my advice is to buy a spare one. Gut that one as you have the time, and once you're happy with it, do the swap. Sell the stock part for the same price you paid. That way, you're not feeling a time crunch to get the gutting done and take a shortcut that ends up being a mistake.
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    So it would be best to keep the 2nd cat instead of keeping the 3rd cat?
    A catted downpipe will replace the stock downpipe/cat and the stock midpipe/cat?

    A cheap aftermarket catless uppipe would be better than a possibly cheaper used STI uppipe?

    Is the whole catback from the STI different than the WRX, or is it just the axleback/muffler? What about the exhaust manifolds/crosspipe?

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    "Supreme Subaphile Extraordinairre" ninefourteener's Avatar
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    Headers/exhaust manifold will net you no noticeable gains. The stock manifold actually flows quite well.

    Uppipe = Should be gutted or replaced on 2002-2005 WRXs, as they can break apart and get sucked up into the turbo. I would consider it preventative maintenance.

    If you must have a cat, get an aftermarket downpipe with a cat..... but then don't skimp on the rest of the exhaust... get a full 3" TBE to fully utilize the increased flow. Your exhaust is only as good as its most restrictive point.

    ... Get tuned. Installing an aftermarket downpipe on a WRX without being tuned accordingly will cause boost spiking, lean conditions, etc. Bad JuJu.
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    Master Baiter EJ257's Avatar
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    Quote Originally Posted by 05WagonRX
    So it would be best to keep the 2nd cat instead of keeping the 3rd cat?
    A catted downpipe will replace the stock downpipe/cat and the stock midpipe/cat?

    A cheap aftermarket catless uppipe would be better than a possibly cheaper used STI uppipe?

    Is the whole catback from the STI different than the WRX, or is it just the axleback/muffler? What about the exhaust manifolds/crosspipe?
    There are two downpipe options for you. There are shorty and full. Shorty only replaces the second cat (uppipe being the first). Full replaces both. Whether it has a cat or not depends.

    An aftermarket uppipe will probably be better due to design. Turn in Concepts made a thread on IWSTI about it. I'll look tonight when I'm off my phone. You wouldn't notice a difference on your stock turbo and/or without custom tuning.

    The exhaust manifold is the same on your car as the STI
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    So there is a "shorty" dp that replaces the 2nd cat and leaves the 3rd cat,
    and there is a full dp that replaces both the 2nd and 3rd cats? but can come with a cat?

    Which would be the best route to go? Should I get a catless shorty dp and keep the 3rd cat? Or, get a catted full dp which would be like keeping the 2nd and getting rid of the 3rd cat? Which of the 2 cats (2nd or 3rd) is most important?

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    Subaru Newb MainFrame's Avatar
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    I would replace them both with one aftermarket high flow catalytic converter. Back in the day I used a TurboXS stealthback exhaust with high flow catalytic converter.. it replaces everything from the turbo back yet retains the stock muffler. You can get it with either a "race pipe" (catless) or a cat pipe that contains one high flow catalytic converter.



    Which one is "more important" is about as vague of a question as it gets. For what it's worth, the closer to the engine (hotter) the more effective a catalytic converter will be at reducing emissions.

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    Ok, thanks guys! I will probably try to find a used oem catless STI uppipe, and gut the 3rd cat while leaving the 2nd cat in the downpipe. Unless I should cut out the stock 2nd cat in the dp and weld in an aftermarket "high flow" cat?

    > Are the uppipe and muffler the only differences between stock wrx and stock sti exhausts? Same downpipe, midpipe etc, just diff uppipe and muffler?
    Last edited by 05WagonRX; 03-18-2013 at 11:11 AM.

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    Is there actually power to be had with a catback exhaust? Or is it all in the uppipe, downpipe and tune? Id really like to keep a stock sti catback with catless uppipe and downpipe, unless it would be much better (more than 5hp) to run an aftermarket catback witht he catless up/downpipes.

    So there wouldnt even be 10 or even 5 hp from aftermarket headers?

  12. #11
    He simply abides. SD_GR's Avatar
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    You asked two different questions. Are you asking about the catback or headers, or both?
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    Registered User frenziedcage's Avatar
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    You will either wanna gut the cat in the up pipe or buy a aftermarket up pipe doing this will make you spool a little bit quicker. Not only that but having the cat in the up pipe is known for causing problems on the 02-05wrx it is prone to collapsing either ruining your turbo or engine. If you want to leave a cat on get a high flow catted dp. However my theory is best flowing exhaust gives you best results. I understand a high flow cat is technically there for a visual inspection but it is still more restrictive then catless. Why not just go catless throw the stock dp back on after emissions? As for your axleback / CBE questions ask yourself this what mods will I be doing later on? Do I want a stealth sounding car or do I want to hear the exhaust? Reason for this CBE doesn't do anything more than create noise at stage 2 anyways.

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    Subaru Newb MainFrame's Avatar
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    I wouldn't bother gutting or cutting the stock downpipe, just get an aftermarket downpipe and a tune.

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    Yeah, I allready made up my mind, aftermarket catless uppipe and cobb catted downpipe. Just wondering if a catback exhaust will give me any power, or if its all in the up/downpipes and tune?

    Aftermarket headers are not good for any power?
    Last edited by 05WagonRX; 04-13-2013 at 03:51 PM.

  16. #15
    Subaru Newb MainFrame's Avatar
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    Depends on your other modifications .. if you're running a large turbo then a good catback and headers can open up a lot of power. On stock turbo the power gains from a catback would be negligible. You can gain some power from a decent equal length header
    . But for you're money you would be better off buying a larger turbo if you're just after more power.

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