Before you dump money into them worthless 76cc chamber heads that come on the 290 hp crate engine I would look for a better set of 64 cc chambered heads. These Summit Racing aluminum heads would be ideal for that 290 HP engine. Like was said you might want to change the camshaft too. It is a 11:1 compression Corvette camshaft from the sixties. you would see a big difference with this camshaft from Summit Racing.Summit Racing® Camshafts SUM-1103 - SummitRacing.com
. Be sure to run the parts thru a compression calculator before you buy anything.