hello i am wanting 340-350bhp on my 04sti type uk and wanting to know what is better a 2.5" turbo back or a 3" turbo back? i must have a spots cat down pipe and can any1 recomend a 1? thanks

 

there are so many different systems out there and so much of the choice is down to personal preferrence (noise, look, style, cost etc).

2.5inch is capable of that figure but 3inch is preferrable... every little helps..
It is possible to lose too much back pressure and lose some low down go off boost but if retaining a sports cat you shouldn't have that issue.

Simon