in practical use, octane rating is a percentage of the time that a gas engine will not ignite prematurely, based on a v8 engine. the
slowing of ignition in gas used to be regulated through the addition of lead and additional refinement, now other additives are used with better refinement. v8s will prematurely ignite more readily than than sixes, sixes more so than fours. this is how i remember it to be.

don