Originally Posted by kannibul

You are totally wrong, and 93 is not better.

Octane rating has everything to do with how slowly the fuel burns and how resistant it is to detonating under compression. Higher octane = slower burn/more resistant.

This is compensated by advancing the timing. The car is "programmed" to use 91 octane fuel, meaning the advanced timing is already active. Using higher octane gas yeilds no benefit as the car can't detect higher rated fuel. *(this is true of all vehicles!)

If the car detects knock, (either by detonation or by the fuel burning too quickly/early by using under-91 octane fuel), the car WILL retard the timing and enrichen the fuel map until the condition is minimized.

That said, it says PLAIN AS DAY in the manual to use 91 octane (or higher) gasoline (again, not because higher octane gas will increase performance, but because it's safer in the sense that it's less likely to knock/detonate), but in case of emergency you can use 87/89 octane, but do not fill the tank, do not drive the car "hard", and fill the tank with 91 as soon as it is available.

So, RTFM.