"Jose" wrote

Engines run better when fast, props work better when slow. If you're
using a belt drive anyway, there's no point in running the props fast.
Let the belt apply the high engine speed to a large, slow prop.

Jose
(I left r.a.homebuilt in, though I don't follow that group)

You are missing the point. Take a small engine, divide the output in half,
and the prop is going to be small. Small props do not mind turning fast.
Also, if you use the belts for the RPM reduction, you have to put the big
pulley out on the pylon, where you want a small one.
--
Jim in NC