Wondering if a 65 hp Mercury lower unit will work on a 90 hp Mercury?

[dan2744]

I found a nice cheap 1966 65 hp Mercury. I want to know if anybody knows if the lower unit will swap out with my 1965 90 hp lower unit.

 

[Faztbullet]

Ratio should be different.....

 

[dan2744]

Thanks, thats what I was worried about.

 

[dan2744]

What kind of affect should I expect?

 

[jimmbo]

Are they both the same driveshaft length?

 

[dan2744]

Yep, it mounted up perfectly and shifts great.

 

[jimmbo]

You will probably need to increase the pitch about 2 - 3 inches, but actually running and noting the rpms will determine which prop. It should accelerate slightly better with the new gearcase. I believe your engine was 4800 - 5200 according to a mercury accessory booklet

 

[racerone]

Dan2744-----The 2 gearcases are Identical in part # and gear ratio.---Enjoy that well built 4 cylinder 65 HP.

 

[Faztbullet]

Have to disagrees as the 900 is a 2:1 ratio and the 650 is 2:3:1. The may share the same housing but gearing is different...

 

[racerone]

No, no, -The parts book shows same part # for the gears on these 2 motors in question !

 

[dan2744]

It ran great all weekend, I can only get the boat up to about 35mph, it's only 16 feet, I thought it would go a little faster.