Blown stern drive

[Glipat]

So last year I wrote off my stern drive. There was a failure of the upper unit. The bevel gears no longer have gears on them.... Anyhow, before I buy a brand new stern drive I was wondering if I could find a used one.
My old stern drive was a alpha one gen 1 with 1.81 gear ratio. This was coupled to a 1990 4.3l mercruiser in a 1990 rinker captiva 185. I was running a 3 blade 14x21 pitch solas aluminum prop. WOT was 4500 rpm
An acquaintance of mine just purchased a parts boat that had a 2.5l 4 cylinder in it with a alpha one gen 1 mercruiser in it but gear ratio is 1.98.
Provided that the shafts are the same length, and I change the prop to a 23 pitch would that bring me in the right ball park? Or would this just torque up the engine????

 

[Scott06]

Probably will work. I repowered my 4.3 to a 5.0, which from the factory would have come with 1.82 and 1.62 drives respectively. I kept the 1.82 ratio and stepped up from a 19” pitch to 21” and it works perfectly

 

[Glipat]

So do I need to drop the pitch to a 19 vice going up? As my ratio would change from 1.81 to 1.98

 

[Scott06]

So do I need to drop the pitch to a 19 vice going up? As my ratio would change from 1.81 to 1.98

No you need to go up in pitch if you have a 21” now , a 23” would probably give you identical performance

 

[Chris1956]

SEI makes replacement Alpha I drives. They are much cheaper than OEM, and may rival used prices.