this is always a hot debate here in central Florida. The group of friends that I usually ride with have a diverse group of boats. First let me say, we build our own boats and have for years. We run alot of dry ground and have run cont. gpu's, Lycoming 0435, Lycoming 0540 (260hp and 290hp) ,Lycoming 0540 supercharged w/gearbox, and Lycoming 180's. Three years ago we decided to try the auto motors, we built a straight drive 500 cadillac and it ran pretty good. Almost as good as the Lycoming 0540. We then built a 410 ci small block chevy. 470hp with a 2 to 1 gear box. It runs better than any of the other boats we have built. It burns less fuel than everything except the Lycoming 4 cyl. The bottom line is ,dollar for dollar the autos will out perform the aircraft. But they are all a blast to build and ride. Well, I guess I've stirred the pot as much as I need to for now.