Cousin Vinny, you said, "Octane is introduced as a chemical, and 92 will have more of it, and it will actually retard the burn in addition to displacing some of the gasoline. That means slightly lower energy content."

This statement is absolutely wrong.

Octane is a specific hydrocarbon molecule. I believe the reference molecule is 1,1,1 Isooctane. When knock resistance became an issue, a reference was needed, just as 100 degrees Celsius was originally pegged as the boiling point of water.

A fuel of 100 octane will have the same knock characteristics in the "official" SAE knock test engine as fuel made up of 100% 1,1,1 Isooctane.

Octane is NOT "introduced" into the fuel. The octane rating is an inherent property of the specific fuel.

Higher octane fuels ignite and burn more slowly than lower octane fuels. They may or may not have less energy per weight or volume depending on the supplier, refineries, etc. Thus, using a higher-than-recommended octane rated fuel may lower power or efficiency because of incomplete combustion.

One thing for sure, using fuel with a higher octane rating than the engine demands costs more.

Another thing, temperature plays an enormous role in determining whether an engine will knock on a given fuel or not. One car I have will run on midgrade in the wintertime but when outside air temps get close to 90F it has to have premium or it knocks even with the knock sensor pulling out timing.

Last thing, many GM products of the '80s and '90s had a very aggressive engine protection plan programmed into their computers. At the first hint of knock, a whole bunch of timing was pulled, like 9 or 10 degrees. The return to "normal" timing was also very slow. In these vehicles, if a lower octane fuel was tried, mileage and power suffered dramatically. Other manufacturers probably did the same thing, I'm not sure.

R.