....well 421 cub on alcohol...lookin around 105-110hp.........supercub 472...lookin around 7 hp more. give or take. plus more torque. gonna have to bore the top case. 100 bucks...get pistons about 300 bucks..supercub head. about 350 bucks. and cyls. 800 or 850. but yes its noticable difference from a 68mm cub to a 72mm cub. if hes doing just racing. it would be worth it...if its a duner bike. i wouldnt ....jus my opinion.