Originally Posted by
RBT
I have run as few as one water hole, but 2 is more than enough. When we were chasing top end numbers there was speed to be found. Can’t say definitively for drags as I have just used the same gearcase profiles.
That being said, consider that the pressure at the water inlet is velocity squared times .0142 or simply 142 psi at 100 mph, 30mph is 12.78 psi. An IMCO gearcase for stern drives has one 3/8 hole to supply a big block.
On the gear ratio experiment. Firstly I would comment on prop slip, this is something I have never been able to understand why people put so much emphasis on. It is super hard to get an accurate measure on what the actual pitch is. ( I have had props run negative slip, and I have had props throw down giant numbers with slips over 20%)
Anyhow, I would like to point out that running a 20 and 1.78 gears doesn’t translate to 2:1 and a 24. The math if I can articulate it here is say your motor makes 100 ft/lbs at 5000 rpm, a 2:1 ratio case would have 200 ft/lbs of torque at the prop shaft with a prop speed of 2500 rpm. Same scenario with the 20 combo, 178 ft/lbs at the prop shaft with a prop speed of 2809 rpm. Real world testing is the low ratio with turn the power band peaky sand the taller ratio with flatten the torque curve and give you a longer flatter pull.
Hope some of that makes sense