I removed the cats to install the race pipes And it is loud! I will probally will put the cats back on. It was a much better compromise for a daily driver. I will leave them off for now. I got on it today I noticed that between 2.5 and 3.5k it goes through a transition wear the car feels like it is choking slightly. And then picks back up again around 4k I am going to mess with the tunning with the cats off and see if I can improve that condition I noticed it with the high flow cats but more with out them. Has anybody who has a Diablo predator tuner and x pipe and catback use the predator to tune their car and noticed a diffrence after the tune? Thanks in advance for your response