A quote from Hot Rods article entitled " Wind Camp"
Concerning aero 'myths' -
" The biggie:
windshield rake: According to Eaker, "Here's a myth I can bust. Once the windshield is past 45 degrees of rake-and many stock cars average like 60 degrees-you will not see an improvement from laying it down at an even steeper angle." We proved this on the Camaro, building a hugely sloped "windshield" out of foam core. It did nothing."
This quote comes from the guy that runs the A2 wind tunnel, and worked on the EV-1 aerodynamics.
( Am I the only one that would love to invite him over to our site ? )
Here is a link to the article :
Car Aerodynamics - Hot Rod Magazine
BTW, Note that this is a several page article