I recently encountered a group of  intelligent, young,  professional minded  men who would add premiuim fuel to their late model truck's fuel tank in an effort to improve engine power and fuel milage. I had previously thought this belief and behavior to be extinct, as on board computer sytems entered the modern vehicle prior to the turn of the last century. If you are one of these people who do this than listen up! Unless your vehicle already knocks or pings when you run it on the fuel grade suggested by the manufacturer you are wasting your money. Auto manufacturers make their money selling cars and trucks in a very competitive and crowded environment.  If a manufacturer makes a car or truck and beats their competitor's model by a mere mile per gallon or by a lousy one horsepower that's all that may be required for the victor to claim the "best in it's class" fuel milage or horsepower. Competition of this sort is especially fierce in the truck segment, where horsepower and fuel improvements to models happen throughout the year.  As one would assume, these  bragging rights translate into very big profits. This is where well paid engineers design and test these systems for optimal performance and earn their money. No one wants to buy or sell second best vehicles. This is especially true for the manufacturer, after investing millions in research and development. You can figure that with this in mind, if all it took was to add 91 octane into your car or truck instead of the suggested 87 and get the extra horsepower or fuel economy,  it would certainly be on your car fuel cap from the begining.


The following link is from the FTC on the matter.
http://www.ftc.gov/bcp/edu/pubs/consumer/autos/aut12.shtm