High Octane Fuel

Every time gas prices creep higher, you might find yourself wondering if you really need to pay the extra change for the upgrade to premium or super duper grade gasoline. The answer to that question is no. Unless you're driving one of the very small percentages of performance vehicles with an engine designed specifically to utilize the properties of higher-octane premium gasoline, there is no performance gain in using premium. It might make you feel better, but your engine won't know the difference.


For the most part, vehicles made after 1985 or so should run just fine on regular 87-octane gasoline. The good majority of engines out on the road today have relatively low compression ratios, and are well suited to use with regular gasoline. There are of course exceptions to every rule: if you're out on the street running a high-compression engine in a racecar disguised as a grocery getter, then you know who you are and know what you need. Understanding what octane is and why there are different grades of gasoline begins with a simplified version of engine operation and straight chain hydrocarbons.

Knock. Ping. Detonate.
In a four-stroke engine, the pistons are doing one of four things: taking in a breath of fuel and air into the cylinder through the intake valve, compressing the air and fuel mixture for a spark induced burn, turning the energy created by that burn into a downward power stroke, or expelling that same burnt up mixture out an open exhaust valve on the upstroke. When a piston travels up in the cylinder it reaches the point called top dead center. At this point the piston can travel up no more and, by virtue of being connected to an ever-spinning crankshaft via a connecting rod, must travel back down the cylinder again. For peak efficiency the compressed fuel should start to burn only an instant after the piston reaches top dead center on the compression stroke and the spark lights the mixture.


Even more importantly the fuel-air mixture must burn in an even flame front originating from the spark created by the spark plug. If the fuel-air mixture ignites on its own before it is sparked, this out-of-time explosion produces an audible knock that makes your engine suddenly sound like a clothes dryer full of rocks. What's happening is that an explosion is occurring out of time and ahead of the burning mixture created by the spark. Instead of one even burn propelling the piston back down the cylinder to make power, two out-of-time-explosions are competing against each other. The sound this competition creates is known as knocking, pinging, or detonation and is unfortunately the sound of engine damage!


Detonation is extremely tough on pistons, valves, connecting rods, bearings, and cylinder walls. If your vehicle is not one of the high performance few, but knocks away anyway when you hit the gas after pouring the 87 octane in the tank, then there are more nefarious causes at work under your hood.