Fireball 500 on the surface appears to be a continuation of the Beach Party movies, since it stars Annette Funicello and Frankie Avalon and co-stars Harvey Lembeck. Besides featuring those three actors, the film has little to do with the Beach Party series. I say little, since Frankie does sing over the opening and closing credits, along with another song in the middle of the movie and Annette also gets to do one song.
Frankie is a famous race car driver who tools around in a George Barris customized 1966 Plymouth Barracuda, towing his race car behind him. He winds up in a town with a stock car race sponsored by Harvey Lembeck. The racetrack has an attached carnival where Annette works for her father Chill Wills, who runs a "hoochie coochie" show. Fabian (who inexplicably doesn't sing in the movie) is Annette's main squeeze. In a plot throwback to the beach movies, Annette wants Fabian to settle down and quit his wild racing ways. I guess it goes without saying that Fabian and Frankie become rivals, not only for Annette, but also on the racetrack.
Fireball 500 has a subplot about moonshine running (shades of Thunder Road) and while Fabian has no problem running "shine", Frankie gets tricked into taking a moonshine run. When the revenuers threaten Frankie with jail time, he has to help them arrest the suppliers.
Fireball 500 is a lot more adult in theme than the movies normally associated with Frankie and Annette. Annette still maintains her "goody two shoes" image for most of the movie, the exception being when she sings "Step Right Up" for her father's girlie show. Frankie, on the other hand, drinks hard liquor and even though the movie only gives you a hint of what happens, it's pretty obvious he has shacked up with a woman in his hotel room.
While it was good to see some old-style stock car racing footage, as opposed to the boring NASCAR professional racing of today, Fireball 500 wasn't very entertaining. Some of the supporting actors were so good it made Annette and Frankie's acting look pretty amateurish, although Fabian held his own with the rest of the cast. The plot mash-up of beach movie with the previously mentioned Thunder Road was weak and even the songs were insipid. Given the choice I'd watch any of Annette and Frankie's beach movies over Fireball 500.