Deeper than the lower-midsection joint!
Deeper than the lower-midsection joint!
You need to get the water HIGHER than the lower unit/mid-section joint. The water pump on top of the midsection, and the you need to get the water above that, or the pump won't prime (regardless of the fact that the pickup is well below that point). I burned water pumps on a 125 & a 9.5 before I figured that out...
You won't be able to test the motor under anything but idle. In gear and with some throttle, 100hp will blow the water out of a 55 gallon drum (and mostly on you) in a heartbeat. Even with a dyno (which takes the place of the prop, so there's no prop splash), I need a big livestock watering tank, with a plywood sheet covering it, or else just the exhaust will blow the water out.
Best tool is a test prop. Back the boat/motor/trailer into the water, cinch the straps down tight & have at it. If you can't find a factory test prop (try eBay), a stock prop cut down to about 70% diameter is a (very rough) approximation. Drill holes in the prop to cut down on the thrust - you want to eliminate as much of the thrust as you can, while keeping the drag. The straps holding your boat on the trailer, and the emergency brake on your car, need to be considered before trying this. Make the cuts and drill holes on the propeller identical, blade to blade, so that the prop stays in static & hydrodynamic balance. One way to do that is to drill a propshaft-sized hole in a piece of plywood, slap that over the propshaft, then drop the propeller on. Sketch the new radius for the blades on the plywood, and the location of the drill holes, and use that as your guide.
