I'm only getting a cat back as of now but the bloke said he would do me a deal on a sports cat and DP if I go back which I think I will be, it's only 2.5 diameter tho is that ok on my car?
Jamjay is 3 inch ok to use straight through as he said 2.5 will be plenty because any bigger I'll expect issues with my car?
Sorry for all the questions but just want a good exhaust and I want it right.
Chuggy.
You'll be fine then, when you go back for the DP & Cat then just make sure they'll flange it.
2.5" - 3" are all fine. I went for 3" because I am considering hybrid & big turbo, it saves on having to buy a cat-back system twice. What issues was he on about? I've had none with mine, it allows the turbo to spool up super quick and get the gasses out pronto. Milltek now use a 3" design which was tested on Stage 2 LCRs so it can't be all that bad.
The general rule on piping sizes that will compliment engine power are:
2.5" for 180bhp - 280bhp
2.75" for 220bhp - 320bhp
3" for 250bhp - 350bhp+
I've read of Evo guys with 400+bhp using 4" pipe but that just seems insane.
Basically it has already been proven that fitting a 3" DP & 3" De-cat/Race-cat to a K04 provides great results, extending the rest of the pipe to 3" will make little or no difference as the worst loss in back pressure has already been at the DP. This might be evident on a car that isn't mapped to suit the mods, hence Stage 2 code to accomodate for this and push the car further.
Edit: By the way, the myth that 3" IS loud isn't necessarily true, it's all in the design of the rear silencer that you choose and IF you want a mid silencer also. Mine is pretty loud but that's down to me choosing a small cylindrical silencer with no mid silencer. I like the sound although if I ever took my car to a track then I'd have a mid box or bigger rear box put in so that I'm safe with noise levels...just in case.