i have a 1988 omc cobra outdrive 2.3L eng which the lower unit is cracked and i have a lower unit off a 4.3l cobra outdrive will it interchange i know i t will mount but will the gear ratio make a big difference i was going to swap the gears but the bearing carrier on the prop shaft is different the 2.3l bolts in and has c clips the 4.3l press in no c clips
Howdy,
Welcome aboard!
Here's a drive ratio chart.
The difference is fairly significant. It's not going to run very good unless you get a fairly LOW pitch prop and you may not get very good efficiency.
If I remember correctly, the 2.3L engine wants to turn 5200-5600 at WOT (Wide Open Throttle)
[Just about ALL engine manufacturers recommend "propping" engines to run at or near max RPM when loaded where you'll operate the boat]
Most small boats with that engine would probably run around 35-40 mph lightly loaded?
Using the prop slip calculator,
http://www.go-fast.com/Prop_Slip_Calculator.htm (2.0:1, 5600 RPM) That would require a 17p prop.
If you wanted similar performance with a 1.68:1 drive ratio, you would need to start with a 14p prop and you still might not get the same performance even if the engine turned 5600 with the 14.
It'll probably *work*.......... But you don't have a lot of excess HP to play with ....... to get the best performance, I would suggest you get the right ratio drive for your engine.
Regards,
Rick
