there's another thread somewhere (on a euro forum I think) about a vintage F1 fan car (Brabham?), where the guy tried to produce measureable downforce. after much work, he succeed- barely. the single large fan was driven off the main motor. he worked his butt off, but ended up with a pretty accurate model that also worked, sort of.
I bet if you put a really big motor on a fan and put skirts on it, you could create some serious suction. (I've got a 1/12-scale-like battery-powered Zamboni desk vacuum that works pretty well.) but would it be faster than a properly set up normal car? good luck with that.
-but it's a really Good show!
speed
I remember when I saw the car run at Watkins glen, it had a snowmobile engine driving the fans.
it worked like h311, but it sucked so much crud off the track in a cloud, nobody else could see where they were going. they couldn't let That thing run for long, aside from the stick-to-the-track bit.