A question about Octane

In college chemistry, I was taught that the higher the octane rating of gasoline, the hotter and more efficiently it burned. I remember my Dad buying Sunoco Super-Firechief gasoline with an octane rating of about 200 (I saw a photograph in Car Craft magazine years ago showing this same gasoline with a 206 octane rating).

My question is this:

Wouldn’t it be more efficient to have high octane gasoline used in smaller, high compression engines? It seems to me that this would help reduce pollution (The gasoline is being burned more thoroughly) and improve gas mileage (you would burn less gasoline for the same amoune of energy produced). Am I wrong on this train of thought?

Hey Slippery Jim,

IANAChemist. Octane is a rating of a gasoline’s resistance to detonation. It actually has less energy (more bonds to break). But it does allow you to use higher compression and get more power. This doesn’t necessarily mean that you get better efficiency.

The high compression engines are also more costly to build and maintain. I don’t know if the dollars and cents support building a more expensive engine to save gas costs, since cars are very price sensitive.

It may be true that you can develop a high compression, small displacement, gas efficient engine, I really don’t know the details. Up til now, high compression (and as a result, high octane) engines have been used for power, not for efficiency.

I think the long term fuel efficient engine design will be a small turbine, coupled with electric motors like the current crop of hybrids.