What type of gas do you pump?

[allmotoronly]

Incorrect. It's the additives/detergents that keep your chamber clean and not the gas molecules themselves. There's a reason why the top-tier gas consortium markets itself that way. Fill 93 octane at a mom-and-pop pump in the middle of bum fcked GA and you won't have a combustion chamber that's any cleaner.

I never said it was the gasoline itself. I am aware that the higher octane fuels usually have additives. I also don't fill up at mom and pop places. I always fill up at BP.

But, the additives are not the only thing that makes the higher octane fuels burn cleaner. Generally, with higher octane fuels, the fuel is burned more completely, leaving less residue. Carbon is a by product of combustion. When fuels do not burn completely, or are burned in a lack of oxygen, more carbon is produced. Thats why the air/fuel ratio is so important. You want to have the optimal mixture of air to the available fuel so that you get the full reactive power out of the mixture. Not enough air, and carbon is produced in high quantities. Too much air, and too much heat is produced.

Have you ever looked at the piston tops/ valves of an engine that has only ran race fuel? If is was tuned correctly, chances are that the piston tops will be very clean, with no carbon build up.