Excerpt from Performance Fuels and Fluids (page 54)
Most people reading this book are likely to be more interested in the possibility of using high-octane avgas in high-performance automobiles rather than the reverse, as a cheaper source of high-octane fuel. (100LL hovers near $2.00 a gallon, whereas racing fuels are likely to be twice that cost.) Aviation gasolines have often been blended with other compounds like toluene or xylene to produce high-octane racing fuels for motor cars. Racers considering using avgas should know that the taxing structures may make it illegal to just use avgas in street automobiles. In addition, as of 1995, the use of any leaded gasoline for highway use is a federal crime.
But there are other potential problems with avgas in high output cars. The distillation curve for aircraft is essentially designed for constant-speed engines, in which acceleration is not an issue, but avoiding vapor lock is all important. Good racing fuels have plenty of light end components to provide crisp light-off of combustion and prevent the mushy-feeling acceleration that can be a consequence of fuel with the wrong distillation curve. Fast, crisp engine response is essential for auto racers coming out of curves, and particularly for drag cars. The other problem with avgas is that its low RVP can and does make for harder starting. Pilots approach piston-engine aircraft in cold weather with trepidation. Aircraft engine block heaters and such are common for colder climates, and lots of cranking is typical on cold days, even in relatively cold climates.
There is still a demand for ultra high-performance aviation gasolines for racing aircraft. “Air Race Fuel,” from VP hydrocarbons, with performance numbers of roughly 120/160, is the highest octane gasoline of any kind sold by VP and has been used for some extremely high output forced-induction automotive engine applications.