Results 1 to 5 of 5

Thread: Cat or Decat Downpipe ?

  1. #1
    Senior Member
    Join Date
    Aug 2003
    Location
    Nottingham
    Posts
    164

    Post

    OK so the time is rapidly approaching to bolt on new bits, one of which is a downpipe, before getting the first remap.

    Would like to go for a replacement downpipe with a cat to stay legal and MOT hassle free.

    But how much BHP less is the same car likely to generate using a cat downpipe instead of a decat ?

    5 ? 10? 20 bhp less ?

  2. #2
    Senior Member
    Join Date
    Apr 2000
    Location
    Zurich, Switzerland
    Posts
    2,190

    Post

    More of a problem is spool time. Better to just run an OE catted centre during emissions checks, you'll pass no worries.

    May get more complicated if you live outside of UK...but hi-flow cats are readily available. Best keep it as far away from the turbo as poss. though.

    Richard

  3. #3
    Adam M
    Guest

    Post

    I have a BPM 3 inch centre section with a hi flow sports cat.

    never used it but apparently it works, and only costs a few hp.

    There is a chance that if it is hot it will pass a roadside emissions test, but more importantly, because it isnt in the downpipe, it doesn't affect spool up time, which as stated above is the most important reason for decatting.

  4. #4
    Senior Member
    Join Date
    Aug 2003
    Location
    Nottingham
    Posts
    164

    Post

    Thanks guys.

    So as a suplementary question

    Open neck (eg H&S) or twin downpipe (eg Magnex) ?

    I've heard twin is better top end, open neck better low down torque - any one offer any fact/experience based advice rather than the hearsay I've read ?

    Thanks

  5. #5
    Senior Member
    Join Date
    Apr 2000
    Location
    Zurich, Switzerland
    Posts
    2,190

    Post

    Open neck with a splitter, which attempts to offer the best of both. Do a search on here and snet for posts from Michael South (I think? someone correct me if I'm worng) for the details.

    Adam - centre cat still affects spool up, but less so. On an STi7 the difference between stock and highflow centre cats an a map with a 1.35 bar target in mid-range, mapped for high flow, only achieves 1.32 bar with the OE centre.

    Never tried without cat....that would be illegal here in CH

    Richard

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •