[lost2a6]

Cool, the 420HP heads were the large square ports and large valves, that engine had no low end torque. The boat would barely plane off with out the trim tabs. The 420 engine had a .095 dome piston with 118cc chamber heads. That engine was around 8.75-8.8:1 comp. The 396 heads have the typical large ovals and the combustion chamber was around 110cc before they were shaved. They haven't been ported, we just did some blending where the large valves were installed. I never took the time to really figure where the compression is but with the flat tops I'm thinking that it is about where the old 420 was. IMO those large square ports don't belong on a marine engine that is turning less than 6,000 RPM. The only thing is the 420 had the steel crank, dimple rods (7/16 bolts) and forged pistons. This engine has the 4 bolt mains but has the cast crank and pistons, and the rods have the smaller 3/8 bolts. As long as I keep the Rpm’s at 5,000 or less then it should be just fine. You'll appreciate the rat rod that my buddy built, I'll try to get some pics for you.