I didn't notice any rpm loss on the top, but it did effect the lower half of the rpm range. I am running a heavy load prop. The reason? I am after a slow constant speed that pulls with authority in the verticals. I am also after maximum quietness. Those two things generally don'r go hand in hand. You really have to have an engine that develops alot of excess power, and then prop it in such a way that you are still in the maximum torque range but at a low rpm that will keep the tip speed down below .6 mach. This prop does just that. It turns exactly at .6 mach but is still in the maximum torque of the engine. The DA's have a aerobatic power curve that allows them to put this torque out at those low rpms. As was said earlier, they also have a long rod to stroke ratio. This long rod to stroke ratio in conjuction with the prop and pipes I am using just happens to run a little better at a slightly retartded position. Were not talking about much change timing wise, or the way the engine runs. These are very slight changes. It's only something you would want to to after everything else has been maximized. You must have the engine fully broken in, you must have the needles dialed in, and you you have to have the pipes tuned dead on...then you would want to mess with the timing as the other things have much more of an effect on the way the engine runs.