sweet o and biturbo's power band kicks in at about 15 (the bottom) just so u know it will rob a lot of low end torque. on the head just mill your stock one unless u can get a puch one for dirt cheap. if u know some one smart with 2 stroke that would do a favor for u, ask them if they will redesign your combustion chamber. (really smart, i have heard of the better of the dutch and go kart racers doing it. but not the average ones)