The one thing you need to consider is what is "high octane" in your area. Commonly, higher altitude locations will run lower octane fuels as "high octane". For example, in Utah the highest octane you could get was 89 octane. However, at 5000 ft. the change in air pressure and resulting change in cylinder pressure made it completely feasible to use the 93 octane program with 89 octane fuel.
I hate using octane ratings as a descriptive rating for a calibration but I don't really have much choice since there really isn't any better way to describe the calibrations. This is the main reason we ask what types of fuel are available in your area and also why it's important to build calibrations for specific locations. Altitude makes a big difference.
As for the difference between 91 and 93? Like Corey said, it's not much. About 1 to maybe 2 degrees or timing from mid to full throttle.
Take care.
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Last edited by Groovy Chick; 12-06-2009 at 04:52 PM.
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