gearing effects

[BLC]

I just replaced the upper gear set in my 1989 1750 bayliner capri with a 2.3L omc cobra. It had 21/21 upper gears. The marine supplier that I ordered them from said that they no longer make the 21/21 set anymore and said that they are installing 21/19 tooth sets instead for this set up. So thats what I installed. This boat is new to me so I don't know how it ran before with the 21/21 set. How will this effect the speed and torque preformance of the boat
I don't know if this matters but the prop is 13 1/4 x 17.

Thanks

 

[hwsiii]

Re: gearing effects

WE need the lower gear set as well.


H

 

[BLC]

Re: gearing effects

Now, I am assuming that the lower gears are still stock. If so they would be 13:26 according to the manual

 

[hwsiii]

Re: gearing effects

Your new gear ratio is 1.81:1 instead of the 2:1 you had before the gear change. You lost about 10% of your torque output and gained about 250 RPM top end if the motor has enough torque left.


H

 

[BLC]

Re: gearing effects

Thanks

 

[BLC]

Re: gearing effects

So the bottom line is that I will have less torque but more top end speed? Will the top end rpm be 250 higher or am I misunderstanding something?

 

[hwsiii]

Re: gearing effects

Theoretically, you gain 250 RPM but you lose extra torque, so usually what happens it is a wash and you keep about the same speed maybe an extra MPH and your RPM will rise a little.


H

 

[QC]

Re: gearing effects

Classic explanation of HP = torque x RPM / 5252 in this discussion . . . Theoretically HP stays the same here. Oh, and propshaft RPM will rise for the same engine RPM, but your engine RPM will actually drop for the same boat speed Lower numerical ratio is a higher gear.

 

[Bondo]

Re: gearing effects

So the bottom line is that I will have less torque but more top end speed?

Ayuh,... Bottom line is, it'll probably be a Dog because that little bitty motor won't be able to pull the taller gears...