Agree with Artisan 100%. By experimenting with fuels and props you can find the largest prop that will not cause detonation. This is the same "knock or ping" that you hear in your car. Very detrimental to engines!! (Wish I had taken a picture of my Yamaha dirt bike in which detonation ate thru the top of the piston. Kinda looked like somebody had been picking at it with an icepick!
One other alternative... if you must use a specific engine and way overprop it, convert to spark ignition. This allows you to set the timing so as not to detonate. A case in point....I have a 1/5 pica spitfire that I wished to use the OS 1.20 supercharged 4 stroke engine. This is an FAI engine intended to swing 14-14 props at 8 to 9000 rpm. I wanted to swing a 18-8 3 blade Zinger prop assy. On glow, at full throttle I couldn't lean the engine past 5000 rpm without detonating. On CH ignition, set at 25 degrees BTDC, I can go full throttle and full lean ~6000 rpm with no detonation whatsoever. I will continue advancing the timing until detonation or no further rpm is noted, then back off a degree or two. Us scale guys will go to ridiculus extremes to make something "scale"!!