If the current production glow engines are designed for 7-8:1 CR and we run them at 2-3 times that as diesel conversions the mechanicals aren't an issue. So I think we could still run higher CR to make more power if possible witout worrying about engine failure as long as oil is chosen accordingly.

Energy density for fuels, especially aircraft, is specified as BTU/Lb. Diesel fuel economy as measured in cars is always miles per gallon. Nobody bothers that diesel has a 20% advantage because it is heavier than gasoline to begin with, besides gasoline and diesel is sold by the gallon not the pound. By weight, heat value is within a few percent. You must specify. Science teachers tought me one thing I'll never forget "the units ARE important". Air is burned with fuel by mass ratios not volume ratios.

Torque may be greater but HP does work. So less HP means less work. The issue here is that a larger diameter prop may be more efficient than a smaller prop at the same power in a particular installation. So less HP could result in similar or even better performance. This isn't a bad thing. In an airplane the prop is the "transmission" matching the diamter and pitch is like selecting proper gearing for a car.

About the ether. If the ether has a high cetane number (CN) of ~95 and we are mixing 35% of it with kerosene which it seems is near CN 40. What is the final CN of the fuel? I would think it's higher than the 2% Amsoil mix, but they run at simliar CR.

The etherless mix I've tested is castor, kerosene, and Amsoil cetane boost. The details are a few posts back. It runs well but I haven't been successful in a cold start on this fuel yet. I haven't tried any more since that day becuase of a cold or something I have going on.