The OE muffler is of excellent design, of course it produces back pressure to reduce noise, but only above where non cammed SR20DEs poop out, or after 6500rpm. With or without a cat the stock muffler is producing results close to the turbo muffler, but MUCH quieter. The OE muffler seems to start increasing back pressure at about 5500 rpm on up. Nissan did their homework in designing that muffler, the back pressure buildup corresponds very nicely with the stock engine performance characteristics. A stock SR20DE starts to choke after 6500rpm, the OE muffler ramps up 1 or 2 psi till about 6500rpm where it sharply increases to its maximum.
I'd suggest trying to find someone to make a 2 1/4" mandrel bent exhaust. Keep your stock cat in there, unless it's clogged, then get an aftermarket (maybe a catco) replacement. It's not worth removing, all you'll gain is pollutants out your tailpipe. I think this has already been talked about on the forum too, if you're looking for more info try a search as i think it's been talked about a couple times before.nelam said:So if I want to get a catback custom made exhaust system, what size of piping should I get? 2.0' or 2.25"? And should I take the cat out as well? I know the stock cat won't do any harm on performance on our cars but I just want to take it out to make things simpler underneath the car. And I just got my smog done.
I have a 91 G20 M/T with Stillen intake and Stillen 4-2-1 header. But I am not done with the mod. yet. I am going to get underdrive pulley, ECU, and cam as well.