ALT-1 The value of using High Octane Fuel
First off, octane is the anti-knock chemical in gasoline, and the number on the pump is more accurately known as the anti-knock index (AKI). This is why race fuel is able to have an octane rating higher than that of 100% octane.
It's obvious that high performance engines, with higher compression ratios and aggressive ignition timing, will require a fuel with a higher AKI, but what about normal cars? Until the past year or so, it hasn't really been necessary for most drivers to consider switching from regular to mid-grade, or even premium, but with the introduction of 10% ethanol to fuels in many places, drivers may find it necessary.
Here's the problem with using ethanol in everyday engines. In order to operate at optimum efficiency, pump gas has to be compressed anywhere from 9 to 12:1. Ethanol has to be compressed as much as 16:1. In normal gasoline engines, ethanol works very poorly without modification. Modern engines sense the drop in performance from the non-exploding ethanol, and they advance ignition timing to compensate. This advance in timing often causes the regular gasoline (the other 90%) to pre-ignite, causing a knock.
Mid to premium-grade gasoline seems to be the solution. The engine will still respond in the same way to the foreign fuel, but it will not be as prone to knocking because the fuel has a higher AKI. The engine can then fine-tune its timing to optimize performance and fuel efficiency, essentially putting the extra money for the premium fuel back into your pocket.
If you haven't noticed a difference in performance with the changes being made to our gasoline, you can probably just keep using low-grade fuel, but you might still consider shelling out a few extra cents for a tank of mid-grade and see if you notice an increase in performance. If you have noticed your car knocking, sputtering, hesitating, or stalling, octane is likely the cheapest and most efficient solution to your problem.
