Maybe a 49cc ported head/cylinder, & raise the engine compression. There are 2 43cc 40mm bore engines, a reed port and a piston port w/ the carb bolted to the head. There are kits for the reed ports that come w/ a FC crank and Cyld and Head everything. I got one last year on eBay for $74 shipped. The 5 port engine on my Lucky 7 avatar bike.