Lower unit compatability

[klook]

I picked up a boat just for the lower unit. It is a 3.0 with the same generation drive as my other with 4.3. I wanted to replace it as the cavitation plate was destroyed by fork lifts and the all aluminum "whale tail" from NZ that was on it when I got it.
My question is, other then gear ratio which I though I could compensate for with a prop, will it still slide right in my upper unit? Is the spline the same I guess.....my boat is an 86 SeaRay and the donor boat is a 89 SeaRay.

 

[matt167]

you'll have to get a prop with a bit more bite. That's a 1.81:1 ( 4.3L ) vs 1.94:1 ( 3.0L )

 

[klook]

you'll have to get a prop with a bit more bite. That's a 1.81:1 ( 4.3L ) vs 1.94:1 ( 3.0L )

Thanks, that is what I thought. Or I can stay with the lower prop and have great hole shot. Watching the high rpms also. I was thinking of going to a stainless 3 blade in the same pitch. People say the stiffness makes them act like an alum in a higher pitch......

 

[Bondo]

Ayuh,..... The gear ratio is in the upper,.....

If ya just swap the lower unit, there'll be no difference,....

 

[matt167]

Yup, Bondo's right.. Any time I hear about I/O lower unit, my mind automatically goes to the entire outdrive

 

[achris]

....will it still slide right in my upper unit?...

Yes.

 

[klook]

An ahaaa moment. I meant the entire outdrive as I considered the piece that comes off as the lower unit. I only need to put on the REAL lower unit to accomplish my goal. Thank you all!