I recently installed a nicely built 350 chevy into my 1984 Bayliner 18ft boat with a Volvo Penta 280 outdrive and i ran into a wierd problem. Boat pulls great up to 4000rpm, as soon as i open the secondaries and go full throttle it revs instantly to the rev limiter (5800) and the boat slows down. Next i tried to roll slowly into the throttle and it did the same thing, seems as if the prop just spins in the water without pushing the boat anytime i go full throttle. If i hold it at 4000rpm the problem is not there, already going 45mph at 4000rpm, and if i roll into the throttle it still does it. Seems like the boat looses speed and it comes off plane and the rear sinks down when this happens.
Am i cavatating the prop? wrong pitch? I'm lost and i'm so new to boats i have absolutely no idea where to start. Boat hauls ass, is very snappy, and runs great, all the way up to the point i go full throttle. Engine will make a HONEST 375 to 400 hp. Am i overpowering the outdrive? Or is this more of a propeller issue? If it is a prop issue how do i pick the correct one?
Any help would be very much appreciated!