Originally Posted by dan03833
If your engine is not knocking and/or pinging there will be no difference in using 87 Vs 93 octane. The only thing the higher octane would do is reduce a tendancy for pre-detonation (knocking/pinging). The engine is designed/engineered to use 87, anything more would be a waste of money.
While what you say is absolutely true, there is a recent problem with this generalization. Most pump gasoline in NA is now supplemented with up to 10% ethanol at low octane numbers. Higher octane gas typically does not blend with ethanol.
Yes, you get better mileage with higher octane gas, but it's not because of the octane rating, it's because of the lack of ethanol.
Cheap ethanol blended gas is a false economy.