I have installed a Holeshot stage one kit with a stock exhaust and the results are excellent! I did the whole job including the air box mod, shortened springs, ignition advancer, shims, main jets, and pilot screw adjustment. The stock carb settings were too lean but now the bike runs great. I have no interest in an aftermarket exhaust because I feel that this set up achieves the best combination of throttle response, mid range torque, and quiet operation.