I thinkthe difference might be that you have the runners in your heads and it takes up the room between the combustion chamber, and my combustion is closer to the actual port.I would have gone the hemi route ifthey had a water blockthat could make 600+ inches. The RPMs or solid block aren't the way to go in a bracket motor IMO, but those hemi 99 heads are capable of more HP. I'll be looking to see what numbers yours produces.