Samy, you've probably seen this a billion times.



Now, what happens when you take away most of the air under the wing?

The front spoiler does exactly that. It pushes that air to the side and reduces the flow under the car. It also creates a low pressure area behind the spoiler. That helps draw air through the radiator and cooling package too.

The cars will have lift at the front due to the car blasting air aside. They will also have lift at the rear from the turbulence of a chopped off roof line and rear end.
The rear spoilers do exactly what they say. They spoil the air flowing over the back of the car. Instead of a laminar flow they smack the air upwards and create a more turbulent flow. This increases drag in front of and behind the spoiler but the air in front of it also pushes the car down. That's why wings are more efficient. They move the air without completely blocking it's path.

Take a look at this Ferrari. At 240 mph the front end has so much lift that the suspension is maxed out.



Read the link to the story behind the car. It ran 267 mph at 66% throttle.
http://bobnorwood.com/Terminal%20Velocity%A0%20Norwood%208_2-Liter%20Power%20on%20the%20Salt.htm

Longer cars have better control over the air flow. That's why Bonneville streamliners are really long.
People complain that the smart car should get 60+ mpg on the highway. It can't because it sucks. Well, it sucks the air in behind it at speed due to the lack of bodywork. It's very turbulent as witnessed by the collection of dirt and grime on the back window.

The Charger is longer than the Challenger and has more surface area to handle the air while enjoying a similar size frontal area.