ORIGINAL: w8ye
The problem with hopping up an engine if you cannot do it yourself, is the cost. It is cheaper to buy a bigger engine.
w8ye has, as usual, hit the nail on the head. The old axam "There is no substitute for cubic inches" applies. The only exception (IMO) is if one is possessed of the the combination of interest and expertise to make the "hop-up project" a worthy venture on it's owm merits even if the finar result does not live up to expectation.
Whatever you do, enjoy!
jess