William Sachs agreed to expeditiously write and direct the film based on a list of requirements from Crown International Pictures, including the Van Nuys cruising topic - which the studio wanted to cash in on before the craze ended - and a certain (and apparently generous!) amount of nudity. He wrote the script in only 7 days and the film was produced on an accelerated schedule; the gambit reportedly paid off, with the film being released before the cruising was halted by local law enforcement.
The trivia item below may give away important plot points.
Bobby's van was not a speedy hot-rod in reality. Since the van would be destroyed during the climax and the budget was tight, the producers purchased the cheapest van they could find with the appearance they wanted, and the van they found would barely even run. Trick camera work and sound effects were used to create the illusion that it was driving fast.