A smoother surface improves the car's aerodynamics, so some crews use a net with holes smaller than NASCAR mandates.
Attached to rear springs; can be adjusted during a race to change the car's weight distribution and, therefore, its handling.
[legal]Oil Heater Outlet
Before a race teams plug a generator into an outlet to power a heating element that warms the oil to its race temperature.
[cheating]Rear Deck Lid
To get the spoiler lower (and thus produce less drag), install a hydraulic jack under the trunk lid. After inspection, activate the jack and lower the lid.
There's a foam block in the 22-gallon tank to prevent gas from sloshing to one side in turns, thus interrupting flow to the engine. This technology came from military helicopter research.
To get more gas in the car, cut holes in the tank's foam block or use an extra-long fuel line and snake it around the frame. Another cheap trick: Just dump in a can of STP.