well
 

from some personal experiences My friend took his stock 1j and put a nice 3" exhaust on it and he definitley saw hp gains and boosted from 12psi to 15psi hitting cut somewhere now and it sounds very nice and spool is very smooth and fast. I would recommend a 3" exhaust For any inline 6 as to be Perfect i think a 3.5 is to big.. but i have yet to drive with one to compare.. 2.5 seems a tiny bit to small for my needs and hp wants

From personal experiance, my mate ??? did he try a 2.5 system? no, so HOW can you make this statment, he may well of got the same result and what sort of expert are you to advise people to fit a 3 " system? I know a guy who had a freind who knew a guy ........

i drove the car. im not saying 2.5 is bad but he say hp gains to the 3"

Everyone needs to chill on this forum. Everyone has their opinion, and they are free to state it just as you are. If you would like to settle this argument, please post up some form of proof for your side or this is just going to keep going back and forth with people calling each other names, and probably end with this thread closed by cre with no real answer to the op's question.

BTW turbophil, if you have the results from your dyno runs it'd be nice if you could post them up here so we can see the difference. It would probably help people on here progress their builds closer to their performance goals.

Ive got a 3inch downpipe if you need one :)

Sure your right but thats is all I'm doing, Im sure members can take from it what they will Thanks Phil

Thanks for the drum roll BTwilson. ;)

I really do try to avoid closing threads. If I feel the question has been answered as well as can be expected and that the thread has been thoroughly derailed with nothing more to be gained I will close it.... but usually I will warn the offending members and possibly issue a ban before I consider closing the thread. I really try to avoid deleting posts and threads as well; I'm not in favor of outright censorship (although some people are working at changing my opinion on that and they're getting close to finding their own posts heavily moderated).

I don't care if people get in an argument over something... you don't have to throw mud though. I'll even let the occasional nasty rebuttal slide, but I if see a trend or you start getting too personal you will be put in the corner (or flat out banned).