1988 V20 steplift/305 chevy, mercruiser drive.

[UBHSTRY]

I am working on one of these, I have been looking for some information on how much power the drive can handle on these boats. Also, what could be done to them if say, you wanted to stuff some decent power in it. IE: Chevy 383, nice aluminum heads, good intake, roller rockers and cam, and a holley 600. Mild on the cam. But capable of spinning to 65-6800rpm.

[THEFERMANATOR]

It depends on which drive you have. The early ALPHA units are rated to 300HP at the flywheel, and teh later ALPHA's are rated to 300HP at the propshaft IIRC. The pre-ALPHA drives are a bit weaker by design I believe though. As for high RPM's, they don't take well to that fro mwhat I understand. Theres a guy at screamandfly that mods the ALPHA drives to 400HP or say and 6500 RPM's, but this is for light applications, a V-20 is not considered a light application for an ALPHA drive. 5,000-5,500 is fine on them, and if you plan on going over 260Hp at the flywheel I suggest running the exhaust through the transom and install a drive shower along with running synthetic lube in teh drive as heat is teh enemy with the I/O's. And torque is teh killer for an ALPHA as the gears in them just are not meant to take the abuse(Ibelieve teh ALPHA's use the same basic design as the 3.0L MERCURY 2 stroke outboard lower unit).

[spareparts]

ferm has it right on the numbers. If you want a reliable package, the 383 might be a bit too much for every day use. Merc sells their own 383(320 hp) and usually puts it in front of a bravo. For what you are doing with a V, a good strong 5.7 would be enough.

[step up here]

x 2 times, they are right on the money. i currently own that combo. 1986 vintage!

[brisboats]

Mercruiser put the alpha one behind the 454 for a time and it was a disaster. The torque of the big block would wipe the upper gearset in hard use. The alpha is good for about 300hp and you cannot run it like an offshore powerboat when you have a hot smallblock even with a drive shower and extra reservoir for the fluid. Car hot rod modifications do not really work all the time for boats, your rpm range is to high.

Brian

[THEFERMANATOR]

Originally Posted by brisboats

Mercruiser put the alpha one behind the 454 for a time and it was a disaster. The torque of the big block would wipe the upper gearset in hard use. The alpha is good for about 300hp and you cannot run it like an offshore powerboat when you have a hot smallblock even with a drive shower and extra reservoir for the fluid. Car hot rod modifications do not really work all the time for boats, your rpm range is to high.

Brian

And that 454 ALPHA had a custom set of 1.36:1 geras in it built just for the extra torque and it BOMBED!