What header pipe can I go with if I have a GYT-R exhaust- I don't want to have to modify the exhaust or the Header pipe so what one will bolt right up?

 

Rap,

DONT WASTE YOUR MONEY ON A NEW HEADPIPE!!!

From your build list, it is clear that you do not have a big piston or cam. In such a case, you do not need a full exhaust. Currently, your setup, if properly jetted, will provide as much if not more torque than any aftermarket full exhaust. Granted, some of the aftermarket systems will develop 1-3 additional hp at top rpm BUT how often are you running wide open??

 

raptor720 is right the GYT-R and stock headpipe are fine for the stock 660 motor. I run a big gun headpipe but the plan all along was bore it out and run high comp piston/cam (being done today). I started with the big gun silencer and a month later added the headpipe---> no appreciable difference in performance. The flow characteristics of the stock pipe are more than adequate for your specs, save your money