Related to the above mentioned aerodynamic and airflow experiments, I once found this a cool article and experiment:
http://www.aerocivic.com/
If my post is considered as being way too off-topic, then feel free to remove it again - you won't hurt my feelings
Actually, since the AC got removed from my car, I've been wondering just like inhotwater about a way to influence motor compartiment temp - e.g use an additional fan in the back to do so...