Usually with glow plug OS-8, the APC 14x6 gives me 11800 on the ground and 13x7 goes to 12000, all in fuel 10% nitro. With 20% and more % nitro the power is not going up
and the engine overheads. Naturally when I doubled the spacer under the head and use cooler glow plug I tried again and 14x6 went to 13000. Hope this direction is OK to go
to up to 30% nitro, or what I would do is to add more castor oil and methanol to the 30% heli fuel, it is cheaper and safer. Anyway, 15x4 is pretty good thing when the speed
is not a goal and for heavy model might be even better to run 14x4W(wide) with OS.91.