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As a general rule of thumb... from what I understand.
2.0 ratio for 4 cylinders 1.84 ratio for 6 cylinders 1.65 ratio for small block v-8 motors or motors that make less than 300 horsepower 1.50 ratio for big block motors 1.35 ratio for boats that go well over 100 mph 1.26 ratio for cats that go really really fast Chris P.S. this is for alpha/bravo/volvo type drives |
Originally Posted by PAST DUE
(Post 3079704)
what is the speed of the DRIVE SHAFT ???? you know the one that drives the water pump impeller?? and the over all gear ratio is not made in the upper uint any more there is more than one lower for alpha gen 2 drives with two gear ratios.
You are correct, there are more than 2 ratio's available for the Alpha 1 gen II lower units. 2:1 and 2.4:1 use one ratio 2:1 ( 14-28 tooth count) everything else uses the same 1.65:1 ( 17-28 tooth count) At 4500 engine rpm, a 1.84 ratio upper will be turning the vertical shaft at 4054 rpm ( 1.84 upper has a 1.11:1 reduction ratio) (17t pinion 19t driven) At 4500 engine rpm, a 1.5 ratio will be turning the vertical driveshaft at 4950 ( 1.5 upper has a .9:1 ratio, ....actually overdriven) (22t pinion 20t driven) So, the 1.84 ratio vertical drive shaft turns slower. It might not be enough to make a difference, but I tend to look into every possible ramification when changes are made. |
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