Originally Posted by G-Oil Guy
The same way an airplane wing does. If you look at the car from the side, you have a swooping hood and a giant opening into the engine bay that just guzzles air.
The swoop in the hood creates a low pressure zone since the air loses velocity as it travels over the swoop thus creating a low pressure zone where as at the same time, air is slamming into the engine bay at a relatively unobstructed path. This creates a zone of higher pressure. It may not be a ton but it's just enough to create lift. Now do that for the entire car. The bottom of the car is a relatively straight path (High pressure zone) and the air passing over the car creates a low pressure zone and all of the individual pressure zones add up to a negative down force vector or in other words, a positive lift vector.
EDIT: video. skip to 45 seconds in.
Bernoulli's principle right? Makes sense, thanks.