I believe you would be better off using a larger prop. When your 20x8 unloads in the air your engine will probably rev to over 8,000rpms. I don’t believe these engines will live long at that speed. I have flown mine on glow fuel/ glow ignition and glow fuel/ spark ignition in 1/4 Bearcat weighing 22lbs. With a 22x10 wooden Falcon prop it revs to 5,700 on the ground and probably 6,200 6,300 in the air. I’ve flown 7 mins on glow ignition and 10 mins on spark ignition with + - 1/8 left in a 24oz tank flying in a scale like fashion.