Sure this has been beat to death but I couldnt find it searching. I have BBK Long tubes into a BBK Catted X pipe on my car to pass emmisions. I had the BBK x pipe on it. Now it is much quieter. I made 370 HP out of my 347 at the rear wheels with the Off road X-pipe. They are running into 40 series flows. How much power are the Cats costing me? I plan on doing 2 passes with them swapping out and doing to passes with no cats. If im running the same times better to be green I guess. Car really does sound like crap and smells funny. Let me know if anyone has dynoed with these two setups.