I have never found speed sheaves to work.
Cut overdrive works, it has for me anyway.
The above comparison is designed to fail. Not very scientific. They dyno run the same clutching with a different clutch face. To take advantage of any change to the clutch faces, you would need to adjust the weights, rollers or neutral and or gear down to compensate.
Also, this is one of those one face OD kits, not a true OD. It only changes the angle of one sheave so your not only bending the belt around, your twisting it on the clutch so that it wont be running paralell to the crank. This style of OD will never be as efficient as real OD which runs the belt paralell to the crank.
If they had done the discount OD in this test they would have seen absolutely no loss in power what so ever as the clutch sheave is not changed. This is where you cut the inside lower section of both of your sheaves and the split collars while they are installed. .035 off each is what will keep the cut line below engagement.
Now gear that discount OD down a tooth top or bottom, adjust the clutching so it runs the same rpms and then lets see what the hp numbers say at similar speeds?
There is another OD that recuts the lower angle and the flat, and another that recuts the sheaves about 1/2 a degree evenly from the top down and then the flat, another that is just different sheaves, forgot the degrees but they are flatter and come on some years of vk sleds. All three of these require neutral to be reset(grind split collars).
If your going to try for top speed or radar runs, OD I don't see as any advantage. Physics is still physics and 1-1 is the most efficient you can bend a belt. But for building a trail sled, Od can give you a little more when the conditions permit and allow for a little lower gearing, if you like that sort of thing.
I found the best situations that OD works for is the show up lake racing. I could run really low gears and get them on the bottom, and OD helped me stay ahead on the top even though I had those low gears.
My point is, Olav really didn't prove anything other than if you change one thing on your clutch, you might lose some power. Not to mention, this whole test was about OD and they tested the track speed to around 100mph. Since we don't know which style of sheave this is, we are not sure the transition on an OD sheave would even be used at that point.
Bored on saturday moring.