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ive got a custom made cat back exhaust system, would adding a sports cat, i was thinking Milltec 200cel add any bhp, plus would it sound any different i.e loudness, any thoughts recommendations and prices would be appreciated, thanks once again
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You will get a bit more noise...but no noticable gain in power unless you are pushing the limits of the standard turbo.
The cats aren't the restriction in engines making under 300BHP genuine, so you'll not see large gains.
With better ICs, de-restricted boost pipework, very high boost etc you may see a couple of BHP and a couple of lb-ft, but there again, you may not.
I got nothing concrete.
Depending on re-map, what you may get is a nightmare in passing the MOT!
My old S3 only just scrapes through the emissions test...with 200 cell cats (previously with 100 cell cats - and it was just the same then...unsurprisingly) so be prepared for the posibility of trouble depending on how 'dirty' your re-map is.