Air Cleaner Assemblies

A hood scoop is an air vent on the hood of an automobile that either allows a flow of air to directly enter the engine compartment, or appears to do so. It may be closed, and thus purely decorative, or serve to enhance performance in several possible ways. more...

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Hood scoop functions

Cool air

One possible use of a hood scoop is to admit outside air into the engine's intake ahead of the air cleaner and carburetor or fuel injection manifold. In most modern automobiles, internal combustion engines "breathe" under-hood air or air ducted from under the front bumper through plastic and rubber tubing. The high operating temperatures in the engine compartment result in intake air that is 50°F (10 28°C) or more warmer than the ambient temperature, and consequently less dense. A hood scoop can provide the engine with cooler, denser outside air, increasing power. A properly designed cold air intake can add 10-20 horsepower (7.5 to 15 kW) to the engine.

Ram air

At higher road speeds, a properly designed hood scoop can increase the speed and pressure with which air enters the engine's intake, creating a resonance supercharging effect that can add an additional 10-15 horsepower (7.5 to 12 kW). Such effects are typically only felt at very high speeds, making ram air primarily useful for racing, not street performance.

Pontiac used the trade name Ram Air to describe its engines equipped with functional scoops. Despite the name, most of these systems only provided cool air, with little or no supercharging effect.

Intercooler scoops

Some engines with turbochargers or superchargers are also equipped with top mounted intercoolers to reduce the temperature and increase the density of the high-pressure air produced by the compressor. Channeling outside air to the intercooler (which is a heat exchanger similar to a radiator) increases its effectiveness, providing a slight improvement in power.

Scoop design

To be effective, a functional scoop must be located at a high-pressure area on the hood. For that reason, some functional scoops are located at the rear of the hood, near the vehicle's cowl, where the curvature of the windshield creates such a high-pressure zone, and may be placed so that their opening faces the windshield (a reversed scoop).

The scoop will be most effective if it is either mounted high enough to clear the boundary layer (the slow-moving air that clings to the surface of a moving object) or if it is a "NACA duct," mounted below the surface and designed to draw the faster moving air outside of the boundary layer into the duct. A shallow scoop that is not a NACA duct may not admit a useful amount of air even if it is open.

Read more at Wikipedia.org