Well with all this talk I think im just gonna stick to my 89 octane Ive been using.

 

The best thing to do is to test it out. Make sure the car is running perfectly and load it with 87 and use a scantool to see the knock counts when you accelerate. Compare that with 89 and then 92

 

Its not the octane, its the premium gas seems to be of higher quality, I can usually get about 50-60 more miles out of a full tank of premium over the cheapo 87. Pays for itself.

 

In most cases, your results would be due to the computer running less or no knock retard with premium. That is where the mileage usually comes from. Fuel, is fuel. It contains the same amount of thermal energy per gallon, it is typically timing that accounts for the difference.

If you follow Aklim's suggestion, I suspect you will explain your mileage increase.

 

Knocking can occure even if you cannot hear it. It might be knocking all day long but audiable to the KS only. When the KS senses the knock it retards the timing. Less timing, less power and so you waste more fuel to get the same results.