my baby brother started with the boat in the family. 18' & Berkeley behind a  454. He had a guy build the motor to 400+ HP and wanted more when he had the money.

I'm a little lost. I could see more HP as you put on bigger and bigger props. I cant see that much difference in impellers. Once you reach 3,000 rpm's the pump is going to pump the same CFM isn't it? Why couldn't a 4 cyl Pinto motor do the same thing and save gobbs of gas?

Im thinking a Rotary Wankel or electric motor... No, I'm not using a Pinto :p

Seriously, what HP can you drop down to before you loose top end. I'm not looking to go 70. Skiing speed would be fine maybe in the 40-45 range.