Modern cars don't detect octane, they detect pinging. The sensor is reactive meaning it has to ping before the computer can adjust timing and even then it puts full timing back in usually within a second of pulling it out. It's much safer than the old days without a knock sensor but you don't want to rely on the sensor, you need enough octane. Besides, once detonation starts, you have to pull more timing to stop it than if it didn't start in the first place.
Correct, my response was poorly worded perhaps. As you say the pinging, knocking and timing retardation all occurs near instantly. So the process is repeated constantly till the knock goes away presumably by user putting the minimum recommended octane. I exclusively run Shell V-Power in my Merc and consistantly get higher MPGs (both manually calculated and through the on board computer) compared to EPA numbers so at least I know it's recovering part of the extra cost by going further.
Agreed. I've noticed better mileage too with the v-power. Though, I think you're giving the average owner too much credit to eventually put the correct octane in. I've known too many people who put 87 in a car that recommends 91 and drive around with audible pinging for most of the car's life not realizing the damage they're doing and the money in lost mpgs they're wasting.
