[jkv357]

Based on my knowledge and research on the subject, this is what I've determined.

You need to base your octane choice on the manufactures recommendation. If they say it will run on 87, use 87. Compression ratio is the major determining factor. Engines that require higher octane fuel typically have higher compression. If you run a lower octane fuel than recommended, and the engine begins to detonate, the "knock sensor" will retard the timing and stop the knock. Either way, you'll lose power and efficiency.

If you run a higher octane than needed you'll lose power and economy. You are looking for the lowest octane possible to just barely keep the engine from detonating - that's where the engine will burn most efficiently. Octane slows the burn rate in the combustion chamber, and doesn't "give" you anything.

(EDIT: a better description of what octane does would be: The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites.)

The only exception would be using a higher octane fuel that doesn't have Ethanol instead of a lower with Ethanol. In that case you'll get better mileage, but not as good as Regular without it.


Jay