only if you knew, you should see the maxima's setup. 2 pre cats plus shitty ass bends on the stock ypipe. Dyno proven 10whp N/A on the Cattman y-pipe alone, plus if you did go supercharged that number would be alot higher. They make 2.5" and 3" but thats not needed if just going N/A. You really dont need custom exhaust. Get your y-pipe, fuck the cat get a strait pipe, then find a good cat back system and be done.

Mine sounds ok I have Y-pipe, racing cat, b-pipe from Stillen, stock muffler (for now)