Quote:
Originally Posted by Michael Beard
Octane is little more than "unburnable" stuff which allows you to run more timing and/or compression without getting into preignition/detonation. For real comparisons, you need to look at burn rates, density of the fuel, etc.
Here's a good resource for additional info on fuels. (I became aware of this page more than a decade ago, and I doubt it's been updated. It's possible that some formulations have changed, so check with the manufacturers):
http://www.smithtex.com/racing/fuelcomp.html |
That's a very good point, choosing a race fuel requires looking at all of the parameters. Motor Octane is the single most important factor, that's what allows you to make power without damage to the engine. The higher the Motor Octane number, the bigger the tuning window.
Specific gravity, or density, is also a useful number. But now days, the specific gravity doesn't vary much between brands of the same octane rating. Any change over or under .10 usually requires a jetting change of 1 jet size. For instance, moving from a race fuel that has a specific gravity of .710 to another brand with .715 wouldn't require a jet change normally. But going from .710 to .720 or .690 would require a jet change normally. And any change in specific gravity usually requires a float level check.
The above reference chart from smithtex is indeed very old, and should not be relied on for comparisons or information. All of the info is outdated, and many of the companies listed don't exist anymore.