An air scoop is an automobile component originally found in aircraft. It is designed to allow cooler, outside air direct access to an engine, in order to boost performance. This is accomplished by the mounting of a raised opening on the hood of a car that allows outside air to flow directly into the engine compartment. These scoops can be mounted either forward- or backward-facing on a car's hood, but must be high enough to avoid the layer of slow-moving air that remains on the body of the car as it moves. This is also known as the boundary layer.
The air scoop can be either decorative or functional, with the decorative varieties consisting of a raised plastic or metal mount with no actual opening for air to enter the car. Functional air scoops can also be closed to the outside when the car is not in motion, and opened by the use of either a lever or switch activated by the driver, or automatically, as a result of an air pressure difference when the car is traveling at adequate speed. These scoops must be mounted in a high-pressure area, such as near the windshield, and can be attached facing either away from or toward the windshield, as the pressure created will drive air into the scoop, regardless of the direction it faces.
Within a car's engine, the air temperature can be 50° F (28° C) warmer than the air outside the car. This warm, interior air is far less dense than the cool air outside, limiting engine performance. The cool air taken from the outside by the air scoop must be funneled directly to the engine's air intake as quickly as possible, so as to receive the full benefits of the air temperature difference.
Problems with an air scoop can include increased noise whenever the engine is running, and difficulty warming up the car in cold temperatures. Also, an intake scoop can allow debris or water to enter the car engine, degrading performance and possibly causing an engine shutdown. An air scoop will often have water channels to mitigate this problem, but they can be overtaxed in a heavy rain, or if the car drives through a large puddle. Although an intake air scoop is used to increase a car's performance, users should keep in mind that any such attachment will slightly increase the drag coefficient of the vehicle, meaning that any performance gains must offset that loss.