Performance numbers

[Bushwacker]

. . . if you're running a big two stroke that needs to run at low rpms at 12-15 kts, the engine may bog . . .

Dave, That's a good point about the engine's torque curve and where you're operating on it. Probably makes a good argument for running a smaller engine also, at least with a 2 stroke outboard! With my old 115 I was running a 15" pitch SST prop and it was turning about 3200-3500 at min planing speed, so it was making fairly decent torque. I normally cruised at 20 kts @ 4500, but on one trip with following seas, it started falling off plane when going "uphill", so I punched it up to 4600-4700 and then it would stay on plane with no problem! I later put some marks on the throttle quadrant and then had someone move the throttle while I watched the linkage on the motor. What I discovered was that up to about 4500 rpm, the linkage went to full spark advance, but the throttle butterflies only moved about 10-15 degrees! During the last 30 degrees of "power lever" movement, the throttle butterflies opened almost 90 degrees! The motor also got a lot louder and was obviously developing a lot more power. (Visualize the sound of a toilet flushing with the sound of the gas pouring thru all 4 wide open barrels of the carbs! ) Denny