One of the nice things about power boating (besides the thrill of power boating) is that the engine is very service friendly in regards to access (spark plugs, etc), the engine comes out in about 20 minutes, etc.
Below is an audio/video clip of my 18-foot jet boat with .030 overbored all iron 460 with tunnel ram and headers. This boat has gps'd in excess of 85 mph...not too bad for a an all iron 460 jet boat without a shoe or rideplate (<---those are key "go fast" boat parts),
and without a prop: Turn on your speakers and click
HERE
Paul