advice on deCat exhaust completion required..
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This is a discussion on advice on deCat exhaust completion required.. within the Engine Modifications forums, part of the Tech & Modifying & General Repairs category; hello. Just bought a deCat 2half-inch middle section off eBay for my 2005 WRX. I now need to know what ...

  1. #1
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    advice on deCat exhaust completion required..

    hello.

    Just bought a deCat 2half-inch middle section off eBay for my 2005 WRX.
    I now need to know what I need to buy next.

    First of all as the lads' car selling it was an 03 WRX, so I assume the 2half-inch is the right size for mine. If so, as I understand it, I now need:

    1. deCat Up pipe (not essential tho?)..
    2. a de-Cat downpipe.
    3. SS de-Cat front section pipe.

    Can I get away with changing the last 2 to get the required extra 30bhp before remapping (if so, know anybody who's selling..) ?

    I'm also assuming (I know, I know) that the backbox thats on my car (this 4-5" monster thing that was on when I bought it) will simply attach to the new decat middle section Ive just bought.

    Also come MOT time, should I expect to change any of the above or will it perhaps scrape through..?

    many thanks, Steven

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  3. #2
    Admiral Ackbar the 1st mycologist's Avatar
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    Quote Originally Posted by JackyWhite View Post
    hello.

    Just bought a deCat 2half-inch middle section off eBay for my 2005 WRX.
    I now need to know what I need to buy next.

    First of all as the lads' car selling it was an 03 WRX, so I assume the 2half-inch is the right size for mine. If so, as I understand it, I now need:

    1. deCat Up pipe (not essential tho?)..
    2. a de-Cat downpipe.
    3. SS de-Cat front section pipe.

    Can I get away with changing the last 2 to get the required extra 30bhp before remapping (if so, know anybody who's selling..) ?

    I'm also assuming (I know, I know) that the backbox thats on my car (this 4-5" monster thing that was on when I bought it) will simply attach to the new decat middle section Ive just bought.

    Also come MOT time, should I expect to change any of the above or will it perhaps scrape through..?

    many thanks, Steven
    I'm confused - it sounds like you are listing 4 cats but there are only three. I would consider the UP essential as that cat can damage your turbo etc. at higher boost. ~2.5" is the stock sizing. I think what you bought replaces the midpipe (with another cat). If so then all you need is a shorty DP (I would recommend a high flow cat there) and an UP. You also need an engine management solution to make everything safe and get the full boost in power.

    Look at this figure and clarify if we are talking about the same stuff:


    The DP (bottom left) and mid-pipe (bottom right) are the only ones that have cats other than the UP (not shown) and that really matter. The middle one is the intermediate pipe and that is a resonator not a cat.
    Last edited by mycologist; 11-19-2009 at 09:37 AM.
    "From a little spark may burst a mighty flame." - Dante
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    Thanks for the description but the section Ive just bought is just a 24" long section of pipe and doesnt look like any of the pieces in your pictures! Will this be the section after the downpipe? Or will it be the mid-section? It apparently replaces one of the cats. Hmm.
    I'll ask my mate to stick the car on ramps so I can have a look and take some pics myself this weekend.
    steven

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    Admiral Ackbar the 1st mycologist's Avatar
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    Quote Originally Posted by JackyWhite View Post
    Thanks for the description but the section Ive just bought is just a 24" long section of pipe and doesnt look like any of the pieces in your pictures! Will this be the section after the downpipe? Or will it be the mid-section? It apparently replaces one of the cats. Hmm.
    I'll ask my mate to stick the car on ramps so I can have a look and take some pics myself this weekend.
    steven
    Those are the stock pieces - all of them from the turbo on. The aftermarket pieces look different. Just look at the bottom two - left is the DP (2nd cat counting the UP before the turbo) the right is the midpipe (3rd cat). There are aftermarket pieces that replace just that MP - they look like this:

    Bosal 3rd Cat Delete Race-Pipe :: Exhausts :: Daddy's Sport Compact Performance

    I don't think you can get past the transmission with a straight pipe but maybe someone did.
    "From a little spark may burst a mighty flame." - Dante
    "The stitch is lost unless the thread is knotted." - Italian proverb

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    ah right - thank goodness for that.
    cheers for that link of the aftermarket midPipe - thats what Ive bought. But its much smaller that the section its replacing - hows it going to fit with the rest?

    So. Does this mean I at least need (1) a deCat DownPipe and (2) a deCat section from downpipe to my midPipe (name?)? Then my midpipe will connect to my backbox and thats it?

    I appreciate the patience here.

    Steven

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    thanks people - off on eBay now..
    Steven

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