1970s Mercury lower units?

[2us70]

In the early 70s the Mercury 50 and 65 hp motors had lower units which appeared to be identical but had different gear ratios. I was able to run the propellers from my E Production 650 on my SD 500 with great success. The same situation existed between the 850s and the 1500s. Was this done intentionally? The speed of the SD boats rose dramatically due to this change.

[largecar91]

I know the old inline 4 80 and 85's(i think the 65 as well) had a 2.33:1 ratio and the 150's had a 2:1. There was a 1.78:1 also on the 135's i think. I always thought that merc did it for a lack of torque on the smaller engines?

[Tom Smyth]

that was my understanding as well. the higher ratio allowed the 4 banger to spin up better.all the 6 cylinder 1150, 1250, 1400 and 1500 were 2 to 1. the 1350 was the oddball with 1.78 to 1

[Mark75H]

That's the way I understand it as well