A stock car, in the original sense of the term, is an automobile that has not been modified from its original factory configuration. Later the term stock car came to mean any production-based automobile used in racing. This term was used to differentiate such a car from a race car, a special, custom-built car designed only for racing purposes with no intent of its ever being used as regular transportation. ******************************** When NASCAR was first formed by Bill France Sr. in 1948 to regulate stock car racing, there was a requirement that any car entered be made entirely of parts available to the general public through automobile dealers, and that all cars must be from a model run of which at least 500 cars of that model were sold to the general public. This is referred to as "homologation". In NASCAR's early years, the cars were so "stock" that it was commonplace for the drivers to drive themselves to the competitions in the car that they were going to run in the race. While automobile engine technology had remained fairly stagnant in WWII, advanced aircraft piston engine development had provided a great deal of available data, and NASCAR was formed just as some the improved technology was about to become available in production cars. Until the advent of the Trans-Am series in 1967, NASCAR homologation cars were the closest thing that the public could buy that was actually very similar to the cars that were winning the national races.