Checking The Outdrive Gear Ratio
It is the (2) gears in the upper unit which determines the actual outdrive gear ratio.
For all practical purposes, the (3) gears in the lower unit are all the same size.
To check the gear ratio of the outdrive with the outdrive still on the boat, (with the engine off ) put the drive in forward gear and turn the front of the engine over in a clockwise rotation with a socket and a breaker bar at least 1/4 of a turn to take the slop out. Now put a mark on the engine front pulley and put a mark on the prop. Have someone outside of the boat watch the mark on the prop and turn the engine over by hand until the prop rotates 1 full turn. If the engine had to be rotated exactly 1 1/2 turns to make the prop go 1 full turn, you have a 1.50 ratio which is what you want for a V-8. Other ratios could be 1.65r for some small V-8's and in-line 6 cylinders, 1.84r for V-6 engines and 1.98r for 4 cylinder engines. ( 2nd example : if you had to rotate the engine almost 2 full turns before the prop rotated 1, you have a 1.98 ratio. )
If the drive
is off the boat you can do the same as above by turning the u-joints in a clockwise
direction while watching the prop.