The shell I got from the guy in Tallahassee had a custom exhaust put on with 2.5 piping from the header back to the muffler. Took the cat out, put in a straight pipe, and sliced the o2 sensor. I had to get a o2 sensor and I ordered the carsound hi flow the other day so that should get the engine CEL gone. Right now the exhaust sounds like doodoo, loud and annoying. I know with the piping being 2.5 its going to make it a little louder but bout how much you think the hi flow cat will tone it down?