I want the perfect propeller size and type for the ft-160 twin.

I am talking of aerobatic performance for the dynaflite decathalon.

I suggested a 20/8 propeller but they say that to much for the engine.

LOLO

We normally run an APC 16 x 8 prop when testing, and expect to see between 8,500 and 9,000 RPM when leaned to peak RPM after a thorough breakin. Any prop that turns the engine in this RPM range and flies your model the way you want is the "right" prop. A 20" propeller will likely be too much load, and give you poor power and possibly overheating.

When you break in your engine, it should have at least 20 minutes of running at full throttle as rich as possible without quitting before you start to lean it at all. Use a fuel with no less than 16% oil content, and 5%-10% nitro. More nitro won't give you much at all.