For quite sometime I have wondered about the difference a higher octane gasoline really makes on a cars performance. Not too long ago we owned a 2007 VW GTI which required a min of 91 Octane fuel. I was always annoyed at having to spend the extra money at the pumps, especially with prices where they are, (mind you they have dropped substantially over the past month or so).
I was always under the impression that a higher octane fuel produced more power and better mileage – according to the December 2008 issue of Road and Track, I assumed wrong.
In the Tech Correspondence section near the back of the magazine, they go into more technical detail on the difference between octane levels, combustion chamber dynamics, etc, but the gist of things is as follows:
A higher performance vehicle that requires higher octane fuel is designed specifically for it. Using a lower then specified octane level will reduce power and mileage. The same is not true however for the opposite. If you put a high octane fuel into a vehicle that requires “regular”, you will not see an increase in power or mileage.
An excerpt from Tom Wilson of Road and Track (Page 151, December 2008):
“…an engine optimized to run on regular fuel is lacking the static compression ratio or other fundamental mechanical characteristics to make use of higher-octane fuel. Burning higher-octane gasoline and advancing the ignition timing (in modern engines) won’t make any more power.”
He doesn’t note if higher octane fuel will make a difference in older vehicles, but if you have a fairly new car, just fill your tank with what is required as listed in your owners manual and you’ll be just fine.