crmachine offers a top end kit for the GT5 engine. http://shop.crmachine.com/product.sc?productId=97&categoryId=16 http://shop.crmachine.com/product.sc?productId=57&categoryId=16 But prices seem WAAAAAAAAAAAAAAAAAY over the the top. Then there's bicyclemotorworks https://www.bicyclemotorworks.com/store/products-page/race-ready-66cc-2-cycle-bicycle-engine/ seems like good deal, has everything one would need. How much would building it home cost, tools included compared to the other two options? Are these kits really worth it, will they really perform better than the stock engine?