Okay I have a 2000 auto,vert GT. Mods: UPR catted Xpipe, weld on flowmasters, BBK intake, zex 100 shot. And I got my a$$ tore out the frame by a Mach1. The mach1 mods were ORX, intake, magnaflow catback. From a roll at 40 mph. My bottle pressure was at 900psi. I mean it wasn't even close. I would say imagine a stock 5 speed v6 racing an auto gt vert. That's how bad he beat me. Then I race a mustang gt hard top, auto ORX, SLP LM. I got him out of the hole, but he came around me hard on the topend. Do I need to get rid of those cats and get a real cat back? I didn't think cats and a catback made that much of a difference.