I was looking for some windtunnel-testing videoclips of front and rearspoilers and such, when I stumbled on a number of interesting articles on Autospeed.com about spoiler and improving 'under car' airflow;

Part 1
http://www.autospeed.com/cms/A_2455/article.html

Part 2
http://www.autospeed.com/cms/A_2456/article.html


Earlier articles:

http://www.autospeed.com/cms/article.html?&A=109937

And...

Undertrays, Spoilers & Bonnet Vents, Part 1
http://www.autospeed.com/cms/A_2159/article.html

Undertrays, Spoilers & Bonnet Vents, Part 2
http://www.autospeed.com/cms/A_2160/article.html?popularArticle