If you're going to tune and do other mods later then I'd consider a 60mm (2.5") if I were you.

I have trouble deciding what to believe. I respect a lot of people in this thread so it's hard to decide - is back-pressure real? If yes, is it relevant? Blah blah blah.


All I can tell you is that I put a brand new XForce 4-2-1 header on my brother's DC4 GSI with B18B2. It has a 2" collector. Then we mated that to a 60mm used magnaflow high-flow cat (CEL unknown) which was already bolted to a 60mm Fujitsubo Power Getter. He firmly states (just asked him now) that the car feels better, pulls/picks up better and sounds better, and is therefore 100% happy. Obviously it will depend on who makes the exhaust - Fujitsubo and some other JDM brands just make very good products and most of them are 60mm.

But for me I'd still be wary of getting something like a 3". Again, I don't know the evidence backwards, but it just seems extreme. So if I were you I'd go 60mm. It seems to be the size of choice for JDM brands and especially if you want to do more mods later. I'll bet you don't regret it.