Originally Posted by PT22064
Finally, it is not necessarily true that a car will consume "less gas" if it uses a higher octane gasoline or if the compression ratio is higher. Gas mileage is a complex function of many variables, and there is no direct correlation with octane number.
Sorry, I wasn't clear when I made that statement. I wasn't referring to less gas due to higher octane fuel. What I meant was that an engine with a higher compression ratio and smaller displacement (which often requires higher octane fuel) can achieve similar performance to an engine with larger displacement but smaller compression ratio... the smaller-displacement engine will typically use less gas compared to the larger-displacement engine, with the same performance. The "less gas" is due to the smaller displacement, not the octane rating. This is a generality and isn't always true, obviously (e.g. when you add a turbocharger to the mix), but that's what I meant when I made the original "less gas" statement.
Originally Posted by PT22064
Also, a higher octane gasoline does not necessarily result in lower emissions.
Sorry, I think I was again unclear. I meant that having the smaller engine generally reduces emissions, but you are quite right, there are a number of factors that come into play. My apologies for any confusion, and thanks for correcting me.
