Here's a link:

http://alternativefuels.about.com/od/glossary/g/octanerating.htm

Iso-Octane is the fuel with the "100" rating

Heptane knocks in everything- - - -even a Biggs & Stratton lawn mower.

The percentage of Iso-octane that produces a specific knock point is equivalent to the octane rating- - - -the rest of the blend is Heptane. It's been that way as long as I can remember, back into at least the early 1950's.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!