It should bolt up to ur existing exhuast(cat), if u can't go above 85 it's probably your cat? Just look on ebay for a bolt in test pipe, you shouldn't be all that loud with the 18" resonator and muffler. I have a 99 SE-L with BC 264 Topspeed header, 91 SE-R K&N fipk intake kit, test pipe, and 2.5 magnaflow exhaust. It's not that loud. The G20 ecu you have will work as that's what I had prior, it was a auto as well. U want a intake cam I have those too?