Originally Posted by SRTpowa
Yeah I talked with the guy at Inmotion(I'm terrible with names) before I ordered my tune and asked him if they can disable the cat. CEL. I told him I was gonna have some test pipes made to eliminate the cats and he advised against it for several reasons. One being illegal(not a big deal in Louisiana), two he said he can't disable the CEL and three he said that the factory cats flow so well it wouldn't be worth it. So I took his advice and came across these on the LS1 forums. At least I'll eliminate the two rear cats, resonator and muffler when I open them up. I've seen 20-30whp gains and3-4 tenths ET reduction on other cars with cutouts, so I figured it's worth a shot. Plus I can cruise nice and quiet without drawing attention.
The inmotion guy may not be able to disable the CEL but it can be done. Kleeman will do it and I am sure there are other tuners able to take care of it.
The stock cats do not flow all that well. You have 2 sets of 400 cell cats per cylinder bank. There is room for improvement and you will see a HP gain.