volvo Penta lower gear ratio

[isleno1]

Can any one tell me why the gear ratios in Volvo Penta drives have so many differences in ratio yet have no apparent standard ratio for each horsepower engine. Such as 1.66, 1.79, 1.82. It seems like they would have standard sizes such as outboard motors having 50 H.P. then a 60 h.p., then a 75 h.p. you know, standard sizes rather than 50 h.p. then a 52 h.p., then a 59 h.p.

An outboard gear ratio for one given horsepower to my knowledge always has the same lower gear ratio as another just like it. The gear ratios don't differ for that horsepower particularly in such small increments. If there is a need for a change in performance, a change would be made at the propeller level.
Being so close together in ratio doesn't seem to make any sense to me.

 

[dypcdiver]

Re: volvo Penta lower gear ratio

You need to go over to the Props forum, they will explain.

 

[jeffnick]

Re: volvo Penta lower gear ratio

Maybe it's a torque thing? Smaller displacement high performance motors make HP at higher RPM's - if the torque is up there too, what effect does that have at cruising RPM torque -- too much load on motor/outdrive with high pitch prop? I'm just guessing here. I know the math can be made to work using pitch.