One thing to bear in mind, and this does apply to airplanes, that in a heavy load situation oil weight/bearing clearances come into play since we need to move the oil through the bearing to remove heat created by the pressure/surface speed. The oil you use in your boat/airplane is probably going to be different than in your car.No, it’s merely an engine building requirement that different between an automotive engine and a marine engine.
Putting an engine into a boat that uses the lake, pond, river or ocean for cooling and the engines run cold as far as block temperatures vs an automotive temperature, the clearance of the bearings and pistons are different.
Now one can probably run a low power setup ok if your not beating the **** out of it, but try this with the 500+ Hp motors and the fuse gets real short. My customers were buying the GM ZZ572 crate motors for like 10K and they were a disaster. Didn’t last 30 minutes in a 38’ V bottom. Of course a properly setup marine engine has a broader torque band than what is required in an automotive build.
It’s just a different recipe and being cheap with a boat motor setup usually means your not boating much