I agree that supercavitation, while interesting in its own right, is outside the
envelope for application to land-bound vehicles used on public roadways.
That said, I'm still poking around the 'net for more info on the original idea,
as it might be inelegantly put; "a plate on a pole."
Edit:
One little factoid from my reading to date: drag in water is ~1000 times that
in air. (I suspect you guys already know this, but it's news to me) This would
confirm that putting model cars in water flow tanks is good for generalized
flow visualization... and only that.