Best bang for the buck from Kitaco, 88cc STD race head kits for the CRF50 CRF70 and 12 volt Z50 come with big valve head with 25mm intake valve and 22mm exhaust valve, STD roller camshaft, 52mm piston and cylinder, and complete top end gasket set. Easy install with no case boring, and Kitaco rated 6.5hp, more than doubles stock 50cc output. Works great with a Keihin PC20 carburetor and matched intake manifold.