The upper housing in my Alpha 1 is damaged beyond repair. It is a 1989 5.0LX. I am reading that there are 1.98/1.71 ratios and 1.5/1.47 ratios, and the V8 needs the 1.5/1.47 ratio.

Here is my question: Are the upper housings all the same on the Alpha 1's? Where is the gear ratio made up, in the upper housing or the lower unit? My lower unit is fine, just the upper housing ruined. If I find an Alpha 1 from a 3.0 or 4.3, and put my lower unit on it, will I be good to go?

Thank you for any help! Mark

Ayuh,..... On the Alpha 1s, the gear ratio is determined by the Upper unit, all the lower units are 1.65:1,.....

When the lower unit ratio is combined with the upper units, ya get,....

The ratios used are the 1.98:1 for the 2.5l, 'n 3.0l motors,....
The 1.84:1 ratio is for the ole 470s, 'n the ole I-6 motors, or the 4.3l motor in a very heavy hull,.....
The 1.65:1 ratio is used for the 4.3l motors, or with the 5.0l motors in very heavy hulls,....
The 1.50:1 is used with the V-8 motors,....

Mark, Gen 1 Alpha upper's are the same. Gear ratio is in the upper. While an upper from a 4/6 cylinder will work, gearing will be wrong. Buy an SEI upper in the correct ratio with a warranty.

Thank you for the information.

I'm going to search CL first, but may end up ordering one from SEI as suggested. What year range Alpha 1 drives would work as a direct replacement for my 1989 5.0 LX?

I'm for sure going to try and find a 1:50, but would the 1.65:1 ratio for the 4.3 motor pull harder with the V8? Maybe pull skiers up better? I'm not going for speed and have a 21 pitch stainless prop. Boat is a 20 ft. bow rider, 89 model average boat, not particularly heavy, and not particularly nice, but gets me around and pulls skiers and tubes when I need to. I rarely run it more than 35-40 mph.

Ayuh,.... Up to 1990,..... the Gen.IIs came out in 1991,..... The Gen.IIs will Not bolt on, nor work properly,....
The MC-1s, the R, 'n the MR, which were previous to the Alpha 1s, will also bolt on, 'n run,... plug, 'n play,.....

If yer current drive ratio is 1.50:1, 'n ya bolt on a 1.65:1, the motor will over-rev, unless ya reprop with a taller pitch prop,.....

Not to high jack thread.
Interesting, I have a 350 mag mpi and the Gen II is a 1.62 with a 19 pitch Rev IV prop and only turn 4700 rpm. If I change to a 1.50
lower unit with it give me more top end ?

Get a new SEI upper for $695 https://www.sterndrive.cc/Mercruiser...pper-Only.html

No. Your rpms will go down and your prop will be too big.

That's the way my ski boat is set up. I have 19" and 21" Mirage Plus, and mine runs 55 mph regardless! I'm not sure if the computer is messing with me, but I've even had a 23" on it....55 mph. Only thing that changes is Rpm. My old runabout was 260 Merc and it had a 1.5, and props made a huge difference.