All YS 4 strokes are supercharged. Some use a separate air chamber and the rocker cover as an accumulator and some just use the rocker cover and intake plenum as an accumulator. But all are supercharged.

I found on the Saito 72 using a 13/6 prop that 20/20 gave me little or no improvement over 15/18 but when I used 30 percent heli fuel (30/23) with low viscosity oil I picked up 600 rpm. I went from 10200 adjusted for flight to 10800 aff. That really surprised me. I also tried 25/20 and only gained a 100 rpm. I think it was the low viscosity oil in the heli fuel that helped. All the fuel was powermaster.

Denis