The Insight like many other cars has an engine "knock" sensor. This sensor allows the ECM to fine tune the engine for best performance based on how the grade, or blend of grades of gasoline in the tank is burning. Basically it adjusts the ignition timing.robwiseman said:
In theory this has the ability to increase the MPG of the vehicle. However, chemically, higher grades of fuel can also be shown to contain less heat. In most cases the anti-knock compounds added dilute the fuel and themselves contain less heat energy. Remember its the fuels ability to heat the air in the combustion chamber that generates the mechanical energy.
So the overall balance of increased performance from more advanced timing vs. lower available heat energy often times translates to little or no MPG improvement on the road. But most often the increased cost of premium vs. regular _never_ offsets any savings from increased MPG.
Finally in regard to increased detergents in premium blends there was a real world problem about 15 years ago with a reformulation of gasoline and increases in engine deposits. Your only protection back then was using premium fuel. However, the problem was so widespread and the most severe forms caused auto manufacturers so much trouble that the big guys duked it out and now even the regular grades of any major brand of fuel has sufficient additives to eliminate serious deposit buildups for virtually all conditions.
HTH
John K. Bullock
Knoxville, TN
aka. Insightful Trekker in cyberspace.
