going by your dia picture i seeing i would cut two inches off your pipe ,in saying this can you hear a differ in sound when your motor is running around 5,000 to 6,000 rpm doe's it mellow out and the tune sound's sweet if so its ok ... i have used this exhaust on a couple of my bikes and differ lengths on the header and dia tubing make a big differance and many motors are not the same results ,you will need to make a couple of length's starting at 11.5" length will be a very good start good luck and hope i have explained easy to you ...you will know when this pipe is working as it should