Same problem here. Have a Motoworks slip-on, now I have a hole in my stock head pipe. I have another quad I had a FMF slip-on, then later added the FMF powerbomb. Fit great. I later replaced the FMF slip-on with a Motoworks thinking they should both fit the same since they are both designed to fit the stock head pipe. Wrong! The FMF fit over the header, the Motoworks fit inside the header. Trying to see if Motoworks will send me just the head pipe, haven't heard back yet. Guess only other option is to get the Powerbomb and have the Motoworks slip-on expanded to fit.