you mean because of backpressure? i can't imagine there would be. those twister mufflers are extremely low john uses 2 of them and a mac 3" muffler on each side of his setup and he is making alot more power than me. if it is good enough for him, i have confidence it will be good for me too. the flo-pro web site says this about their twister mufflers, "Insignificant Loss Of Horsepower [compared to] Open Headers"