How much energy can be extracted from the fuel as a percentage of its volume or mass. Heat of evaporation. Chemical stability, neutrality, and cleanliness. The first three factors are often confused and interrelated when, in fact, they measure three completely separate things. There is no natural collelation between them.
Octane rating is in no way correlated with engine power or efficiency.
First, you go out and get a suitable supply of the fuel which you wish to test. Finally, you and your buddies arbitrarily, agree that iso-octane has an octane rating of 100 while heptane has an octane rating of 0. Next, you call up Waukesha Motors and order yourself an ASTM-CFR test engine. One protocol is called the motor protocol and the other the research protocol. You vary the compression ratio until the onset of knock and write down all kinds of various scientific parameters.