I can't find what you describe. Any chance it was the Coventry University study? And Audi A2?
It was posted here, the links are stale but there's a summary in the first post:
Drag reduction modifications in wind tunnel: Audi A2 from Cd 0.288 to 0.204
There's some discussion here:
http://ecomodder.com/forum/showthrea...tml#post308635