The biggest problem with stock BBchevys is that the valve guide is tall and won't allow much of an incerase in lift, may be only to .490. You need to check it by having some one measure from the top of the retainer to the head, then while you compress the spring until it hits the top of the guide and remeasure, subtract .060 and thats all of the lift you can have without machining the guides down. Do both the intake and exhaust the amount of clearance will probably be different. Your big problem is the cast hypereuctetic pistons, even the trucks have them. They will explode at about 400-450 HP, or with ANY detonation. Intake and carb- you can usually get away with, cam usually explodes the Hypereuctetic pistons. Even the stock 330 HP boat motors have the junk pistons too. Also a car or truck ignition curve is way different than a jetboat wants, it not only limits the available horsepower, but kills the fuel mileage too. Good luck. TIMINATOR
