When I purchased my car last summer it came with a 3" downpipe to where the cat used to be, from there it turns into a 4" pipe to a giant pacesetter muffler with a 5" exhaust tip. I am thinking about buying a Power FC because I have read on here that with those mods you really should upgrade the ECU. I was reading another post on here about the A/C wiring being wrong and in that post there was an instruction sheet that someone had uploaded. In that instruction sheet it mentions that if you are running a no cat system that you will have to have the Power FC professionally tuned. Is this true? Is anyone else running without a cat and the power fc?