Re: 115 vs 150
My question is whether your old boat is equipped to handle a big 4 stroke. If you have a mid 80's twin toon boat with 19" or 23" toons, you may not have the buoyancy to handle a heavy 4 stroke motor.
My old Starcraft 24' boat with U tubes is only rated for a 115 hp motor. I would be better suited to replace that motor with another 2 stroke due to the weight factor. 150 hp would be entirely too much power, and essentially a waste of money.
A 150 hp motor would work best on a tritoon with lifting strakes where you'd be experiencing 40 mph max speeds. That engine on a twin toon boat would do good to hit 30 mph without lifting strakes.