Originally Posted by TheSasks
Some vehicles do get better mileage towing running higher octane, we use mid grade 89 if we can get or high if not. The reason is simply the higher octane keeps the engine from detonating under load and which causes the computer to richen the mixture and pull timing out so you get less power and more fuel burnt.
that's it. octane rating is a ping measurement. in the very old days, they put lead in to smooth out the explosion. not sure what ethanol will do. it is interesting on how some additives will increase octane in small amts but go the other way in larger amts.