Replacement engine Questions

[Camlew]

Hey new to the forum. I have a 1975 fiberform 22.5 ft cuddy hardtop. It has the Ford 351 mercruiser engine in it with the alpha leg. I had an over heat issue and might need to replace the engine . Looked at a 5.8l. ford redline ho 285 horsepower. It's a 1990 something out of a jet boat. Any reason this won't work with what I have.

 

[QBhoy]

Hi...I was a little reluctant to even reply to this...but thought I would add some thoughts, that others more knowledgeable than I might either build on or put a stop to or correct right away...
I may be wrong and/or confused by nature or perhaps being just in from the pub (for the first time since covid ruled the world)... but I don't ever remember Mercrusier putting a badge on a ford 351 and alpha package. I may be wrong ?? perhaps to add some confidence to my thinking...a 70's set up would not ever have an alpha drive either...they weren't around back then. a ford 351 in boats I have ever known...have either been used in omc or shaft drive ski boats...probably other uses too.
Anyway...to answer your question around using an engine originally intended for a jet drive, to move to an outdrive....my first concern or wonder, would be around its cooling system. most jet drive units I know are cooled by means of positive pressure, scooped flow of water into the engine, branched off the jet pump discharge...or separately from an intake grate or scoop on the hull. An alpha drive would alternatively take cooling water in from it's lower unit grates and lower unit located impeller.
So you would need to think about the cooling method for starters...

 

[achris]

I'll add a bit too @QBhoy s post..
Merc did use the 351, it was the MerCruiser 233 (2bbl) and the MerCruiser 255 (4bbl). MerCruiser stopped using any Ford engine in 1977, so they all came out either as inboards or with a drive, like an MC1 or the TR (or TRS).

My main concern wouldn't be cooling. If you're just going to use the engine itself and put it in front of the existing drive, the water coming up from the pump in the drive would be fine. No, my concern is the power of the engine, it's too much (not for the drive), which leads me to think you'll lack enough power at low engine speed to be effective as a stern drive power plant. Remember that jets don't put much load on an engine until they are really revving. A propeller puts load on right from idle. Not enough power in that low range and the boat's going to be difficult to drive. Just ask @QBhoy

Chris....

 

[Camlew]

I'll add a bit too @QBhoy s post..
Merc did use the 351, it was the MerCruiser 233 (2bbl) and the MerCruiser 255 (4bbl). MerCruiser stopped using any Ford engine in 1977, so they all came out either as inboards or with a drive, like an MC1 or the TR (or TRS).

My main concern wouldn't be cooling. If you're just going to use the engine itself and put it in front of the existing drive, the water coming up from the pump in the drive would be fine. No, my concern is the power of the engine, it's too much (not for the drive), which leads me to think you'll lack enough power at low engine speed to be effective as a stern drive power plant. Remember that jets don't put much load on an engine until they are really revving. A propeller puts load on right from idle. Not enough power in that low range and the boat's going to be difficult to drive. Just ask @QBhoy

Chris....

That was quite helpful thanks