2.5' v.s. 3' downpipe and cat

[EPSYCHOBOB]

i was wondering what is the best setup for a 97gst that is basically stock except a hks intake and boost guage. i was thinking of starting with a downpipe and a high flow cat and i was wondering if there is a big differance between the 2.5" and 3". i plan on getting a hks 3 inch cat back (if that helps) in the future.would i still need a high flow cat if i am going to install a catback system? i want to try to keep my car as legal as possible because i live in california.

 

[RoasT BeeF]

Wow a 2.5' downpipe? damn thats huge!

3" is the best, but 2.5" works very well over stock. I have a 2.5" now but plan to swap to a 3" in the future. You should get a catback no matter what. If you are really worried about emissions you could always go with a test pipe instead of a highflow cat and then just swap it back out with the stock cat when you have to do emissions.

 

[SinEclipse]

sup man i live up in long beach california im running a 3" inch set up. i got apexi n1 catback and downpipe. the downpipe eliminates the cat. but even tho its stock running 3" would give you a better flow also just get a high flow cat. since emission here is wack and if the cops ever find out you have no cat. its even worse.