i am a former fs owner and what fs calls a "30cc", isnt really 30cc. the piston from the fs motor will fall into the cylinder of a 28.5 from cy. and they don't appear to have any longer stroke. it was also a very "poochie" motor. and they afe afour bolt style that may make getting upgrade headkits more of a problem. do yourself a favor and put a good headkit on your cy. i had better performance on mine with a cy 23, and later moved up to a 28.5 and that was fun! however the 28.5 proved to be more than an fs can handle, and i started breaking diffs. so i got rid of the fs and now im getting a redcate tt and im going to put my 28.5 with a walbro 813 and x can on it!