I replaced my original Mercruiser Outdrive (1967 160 Hp in line 6), Gear Ratio 1.65:1, with a used, pre Alpha OD 1.5:1. With my old prop 15.8 Dia X 15 pitch Wide Open Throttle, RPM = less than 3000, 0 vacuum on the gauge. I got a new prop 15 Dia X 11 pitch, tested it on the water today. WOT =...