Lower unit question

S

Steve Cellar

New Member
May 27, 2022
19
Ashland, Ohio
Boat Info
1989 Sundancer 250 da
Engines
7.4L Mercruiser with Bravo 1 outdrive
I have a 1989 250 DA with a Mercruiser 7.4L with a single Bravo one outdrive. I’m looking to replace my lower unit. My current outdrive is really corroded and was apparently badly neglected by the previous owner and didn’t believe in anodes. I went to replace the anode behind the prop and found that there was no real metal there to attach it to which led to finding a crack as well. My question is, what is the ratio that I'm looking for? I’ve been told that the 350's and 454's are 1.50 and others say it doesn’t matter. My fear is that I buy one, only to find out that it doesn't fit correctly. I’m far from a marine mechanic and need some solid advice from those of you with far more experience than I. Any advice would be greatly appreciated.
Thanks, Steve
 
Steve Cellar said:
I have a 1989 250 DA with a Mercruiser 7.4L with a single Bravo one outdrive. I’m looking to replace my lower unit. My current outdrive is really corroded and was apparently badly neglected by the previous owner and didn’t believe in anodes. I went to replace the anode behind the prop and found that there was no real metal there to attach it to which led to finding a crack as well. My question is, what is the ratio that I'm looking for? I’ve been told that the 350's and 454's are 1.50 and others say it doesn’t matter. My fear is that I buy one, only to find out that it doesn't fit correctly. I’m far from a marine mechanic and need some solid advice from those of you with far more experience than I. Any advice would be greatly appreciated.
Thanks, Steve
Click to expand...
Ratio is set in the upper end. Lower end should be a general swap. the 1.5:1 is the baseline for the B1 + 7.4/454

My Chaparral 2550 had a 1.5:1 Bravo1 with the 19" S/S prop and was a rocket on top end.

Ratios don't get crazy till the B3 is in the mix. My B3 is a 2.0:1 with 28" pitch props
 
With a boat your size, I would be strongly considering going to a B2 or B3 if replacing the lower. It is my understanding that they are all interchangeable. You may lose a knot or 2 at wot, if that is even a thing for you, but the low speed maneuverability and hole shot gain is day to night.
 
Thanks for the info. guys, I picked one up at my marina today and getting it installed next week along with pressure tests and checking the seals of the upper. Thanks for reaching out.
 
Steve,
I JUST went through tis. 91 same boat, motor, drive. Needed a prop seal. Was too corroded to remove the seal. B1 Merc lower is expensive. B2/3 even more. My mechanic recommended SEI. I asked around a lot (thread on here somewhere).
for a new lower with 3 year no fault warranty it was 1250 for lower, plus tax and shipping. Mechanic charged 500 labor. So for a little under 2k, i am good to go. Highly recommend this route.
See General Discussion, page 6, SEI outdrives.
5418DE0F-FD72-4BC9-8F13-3FB693AF6EE9.jpeg
 
I did exactly as you did. I got an SEI for $1228 shipped. My marina is doing it for me.
 
As followup, today I completed the 10 hours breakin. And went for a nice long ride on plane. Running like a champ, using no gear lube, no strange noises, gets on plane at 2400rpm, ran at 2800rpm / 22mph per gps.
I’m happy.
 
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