Re: 1969 20' engine choice
Some things to look at when deciding on an engine size that are not usually brought up, are gearcase size and overall weight.
Some smaller block motors share the same gearcase size with their larger cousins, but with a numerically higher ratio. This lets them use the same props, but puts the RPM range significantly higher for an equivalent speed. This can make the predicted fuel savings of the smaller motor dissappear.
Other times, the smaller HP motor is on the same block as it's larger cousins, and so weighs the same, just has less power.
Best overall results usually come with the most power in a given sized block selection. That configuration has everything working in it's most efficient combination.
I have an 18SF with an Eagle series (60 degree V6 block) Ocean Pro 150. It's nice in that it's about 75# lighter than the 90 degree V6 blocks (200 and 225 hp). It runs low 40's (wot) on GPS and has it's sweet spot around 3000rpm.
I can't imagine putting any less power on a boat any bigger.
Darlene
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