I was wondering the otherday about a downpipe if i were to get a downpipe without a cat or a offroad pipe and would use a O2 Sim will this hurt gas milage or would it be better to run a downpipe with a cat? also which would give me more power without loss of gas milage a 2.5 or a 3" ? i just had these coupple of questions on my mind and i figured i allways get great help on here