Regular or High Octane gasolene

[Janius]

In the "old" days of mechanical igntion and mechanical distributors, there was only very limited control of timing. Therefore you either set the timing for regular gas (and got lower performance and gas mileage but no knocking) or for premium high octane gas and got better performance and gas mileage (but NOT at the same time!).

Modern cars have a knock sensor which controls the ignition advance. The ignition system will push the timing ahead until a knock is sensed and then will back it off. It will continually try to advance the timing as far as it can all the time. Higher octane gasolene resists knock and therefore should allow the timing to be advanced further than regular gasolene. More advanced timing gives higher engine output. Following me? Therefore, using premium gas in my (for example) Honda Accord will produce more power across the entire spectrum and better gas mileage overall (if I don't use the extra power by standing on the gas pedal more).

However, everything I read says using premium gas in a car designed for regular will not improve performance or gas mileage. Can anyone explain if using premium in an engine designated for regular will improve performance?

[Janius]

Haltamer, again back in the old days, increasing the advance by turning the distributor would make a notable improvement in performance. However, maybe modern cars are so well set up that the improvement would not be noticeable. And in response to "Toomany2CV", yes I am indeed stateside (New Jersey to be exact).