The higher the octane rating, the slower and colder the fuel burns. If you run too much octane in your engine, it won't run very well because the burn is way too slow. If the octane is too high, the piston might already be at bottom dead center (BDC) and the fuel might still be burning! If the octane is too low, the fuel will burn too fast and too hot which causes detonation and leads to sure-fire engine damage! Aviation fuel is another no no. A famous engine builder (top fuel engines) told me a story about an engine that was in his shop that had major melt down in the cylinders. He said, "Arron, av. gas is for air planes! Where do you see airplanes? Up in the sky! Do you see cars up in the sky? No! How does your car run when you're up in the mountains? Yeah, like crap! There's no oxygen up there. Aviation fuel is designed to be run in a low oxygen atmosphere. What happens to that cutting torch flame when you add oxygen to it? Yeah, the flame gets hotter and turns blue! What do you think happens to an engine in a high oxygen atmosphere burning aviation fuel? Look right here at this engine and you'll know!"
He made a good point.
Octane boosters of today are usually made of two things, either alcohol of some sort of flame retardant. Alcohol works OK I guess but the flame retardant stuff that turns your sparkplugs red? Don't go there! The object is to burn all of the fuel in the cylinder, not put it out! The old octane boosters, the good ones, are all outlawed. The best that I can remember was something called Aniline Oil. This stuff worked great but you had to use a fresh air mask and wear gloves because it displaces oxygen. If you spilled it on your skin, it would turn that area blue!