Chrysler lower gearing

[Mac_55]

i have a couple lower units and im trying to figure out gear ratios for more speed

14' commet 1976ish 70hp chrysler, 2 blade brass or 13x21


2 piece 70hp
1 piece 75hp .
and 2 piece 135

any taker on which would be a better ratio for more fun , swapin lower units is like tieing shoes at this point for me,


thanks

 

[Frank Acampora]

Re: Chrysler lower gearing

I believe that all those lowers are the same ratio -- 1.76 to 1. As far as I know, the only 2 to 1 lower units for Chrysler engines were on the 3 cylinder 90 horsepower.

SOME one piece 85 lower units (Force) were 2 to 1. HOWever, the one piece will not swap with the two piece lower.

going up in ratio from a 1.76 to1 to a 2 to 1 will definitely improve top speed but you will need to play around with prop pitch too and really, you would appear to be at the maximum pitch for that engine.

 

[Mac_55]

Re: Chrysler lower gearing

would i be able to swap my chrysler 18spline propshaft and driveshaft into the one piece force lower unit (1980s)?
i just have so many 18 spline props over the years that i don't want to start a new collection, even if i have to use the force mid section

 

[Frank Acampora]

Re: Chrysler lower gearing

WOW! Over a year later.

NO, the 18 spline lower unit is completely different. none of the components will fit into a one piece lower unit case. And, as I said, the mounting bolt pattern for the two lower units is different. Thus, you can not simply swap them

HOWEVER: The two piece driveshaft is about one inch longer than the one piece and the crankshaft splines are the same. It may just be possible to make an adapter plate to mate the two piece lower to the one piece midleg. Again, the water tube is the same diameter but the water pumps are a different height. It may be necessary to either lengthen or shorten the tube.

Hmmm! I have often thought of doing this but never tried: There is no incentive because the two piece lower unit is slower, does not look as good, supposedly "blows out" at speeds over 60 (if you can ever get that high), and the thrust pin-spline driven prop is simply put--regressive..

However, this just might be a winter project.

The hubs for the 15 spline props are much larger than the 18 spline hubs but you may also be interested in modifying one, as an experiment , to fit into the older 18 spline prop. This would certainly be an easier option.