Higher octane fuel simply means that it takes higher pressure and heat before the fuel will combust or detonate on its own without the assistance of a spark plug. Take our Viper engines for example. Compression and temperatures in Viper engines are higher than in most cars and as a result require higher octane fuel, such as 91. If you were to use 87 octane in your Viper, for example, the potential exists that you’ll have combustion or detonation in the chamber due entirely to pressure and heat before your piston is at top center and the spark plug ignites. This early detonation results in “blow by” (the piston ring) or “knocking.” Super-high octane gas like race fuel is designed for super-high compression engines, which would otherwise suffer from early combustion or detonation with lower octane fuels. Similarly, as suggested by 1Tony1, adding a blower may require the use of higher octane fuel to prevent early detonation if the increased pressure created by adding the blower would be enough to cause early detonation otherwise. Using a higher octane fuel than is required by your engine’s compression and heat doesn’t add anything (e.g., if 93 octane doesn’t combust early, neither will 100 octane, each will wait until sparked by the plug and each will expand the same). Of course knowing this, and knowing that my SRT only requires 91 octane fuel, I still can’t help myself and still put in the 93 octane for few pennies more per gallon. Nothing but the best for the beast I guess! Well, within reason. My Viper and my wallet will NOT be experiencing 100 octane fuel at $5/gal. Well, maybe one gallon some day, just 'cuz.
