I was prompted to re-visit this after reading that it was Quentin Tarantino's favourite racing movie. I think he liked the fact it was so different - he compared it to an Antonioni movie. It's certainly very arty, full of short scenes and non synchronous sound - I think there's no scene of people talking going for longer than 30 seconds, and plenty of rapid cuts and voice over... which presumably helped the unit when they went "sneak filming" in Europe. i.e. stealing shots of cars racing around monuments.
Roger Corman helped finance this and did some uncredited direction; it's a kind of a follow up to Corman's The Young Racers, which like this was shot in Europe. Fabian - in the middle of a seven film contract with AIP - is very good as the cocky race driver who is meant to help his more senior partner win but can't help winning himself. That's the gist of the plot - plus a romance with a stunningly beautiful Mimsy Farmer. (He also has flings with a few other girls who are less attractive and poor actors to boot).
Plenty of scenes of cars zipping around, groovy music and credits, great production values (it was shot all over Europe, there's trips to bull fights as well as the obligatory night clubs), consistently interesting technique (in the style of A Man and a Woman). It's beautifully shot. There's not a lot of drama going on and only Fabian gets a full fleshed character - the way the movie is made causes you to feel distance from it. Still, it's worth seeking out if you're interested in a race car movie that is very "late 60s funky".