[oldman]

So to recap, and this is on a M6, but also note many ZL1 guys (auto and manual) say the same thing. LT with no front cats and then stock after that sounds bad. For me in specific M6 LT, no cats, the engine would NOT produce HP at say 1200 RPM, this would mean I can't use 6th gear to 67 MPH (from memory). As soon as I put cats in, problem was 90% solved and I think 57 MPH I could use 6th. Anyway even near stock with front cat deletes the M6 would have some strange low RPM resonance, so at 57 MPH to 65 MPH it was better to leave it in 5th gear. So many road here are 60 to 65 MPH I would only use 5th gear as the top gear.

I've tried the Borla with no front cats, and the Borla with and with out front cats. I think the Bolra works surprisingly well, we all know that resonators really don't work well, especially straight thru and short (Borla is both). I think the 2 and 3/4 helped a bit here. The car is near stock with the Borla and no front cats in terms of sound and low speed drivability, The car is stock with Borla and all 4 cats and stock suite case, but on my setup WOT the car is still CRAZY loud, I have start-up and rev sound clips posted.

I'm sure LT no CAT and the Borla will be OK in terms of drivability, I'll still run cats, I just don't want to tune my car with cats (afraid I may damage them).