Websites and resources I've found useful for information on aerodynamics:
W.H. Hucho, author and editor of the first 4 editions of Aerodynamics of Road Vehicles, is one of the most respected aerodynamic engineers in the world.
Julian Edgar's online magazine archives more than 730 issues. They encompass all sorts of modifications and technical write-ups, many of them related to aerodynamics.
Watch these videos and/or subscribe to this channel for fascinating presentations on aerodynamic theory and testing, as well as other automotive subjects such as suspension design.
The most comprehensive resource for automobile engineering papers on the internet, including aerodynamic studies.