Offshoreonly.com - 500HP's to 575's???

Maybe I did not say well what I was trying to relay.

I have not found any professional marine engine builder or an marine engine builder with a dyno to say they get 650HP out of a 502 that will be used in a boat reliably.

You can get to that number if you spin a Solid Roller cam up way past 6000 rpm. In reality, It will not have any more torque available past 4600-4800 rpm. It probably would make less torque than a good 600 hp motor to achieve a HP number that would be needed to get that 650 hp number. About 5400rpm it will stop pulling in a boat because the peak torque curve is falling off. I would look at the HP around 5400-5600 to be the top usable HP in a boat. Shooting for 5400-5600 rpm will give the largest torque number and will work much better in a boat. Torque is more important than HP, so my suggestion is to work on the peak torque number, then try to keep it from falling off too fast past 4800 rpm.

Scoogin Dickey has a 509 602HP. Alum Heads 10.2 compression using automobile headers.

Teague offers a 509 620HP Version.

These are my thoughts for what they are worth.