I bought a brand new OS 1.60FX and broke it in with a Zinger 20X6-10 propeller for about 90 minutes total run time. Very, very sweet and powerful engine, but - of course that is precisely what I have come to expect from OS after 47 years in the hobby.
Just to establish a reference point, I mounted a 22-10 Zinger and ran it at full power - 5,000 RPM but of course quite high fuel consumption.
I than switched to the Davis Diesel head and ran it with my Xoar 24-6 cut down to 23-1/4: 5,000 rpm slightly rich, 6 minutes @ 4500 rpm on a 6 Oz. tank. Compares very well to what I got on the ST 3000.
I ordered a Zinger 24-8 and 24-10 and will test them next on exactly the same setting.
My goal is still to fly a Hostetler's Fairchild 24 (27% scale) at SCALE SPEED with a SCALE PROP. Hopefully it will fly in a scale manner at 3500 - 4000 rpm which is a very sweet spot in terms of noise (almost scale) and engine longevity.
Here are the first ever pictures of a 1.60FX Diesel that I am aware of. All my attempts to find anyone who ever operated this engine as a diesel on the Internet have come empty handed.