Hood scoop
Encyclopedia
Hood (vehicle)
The hood or bonnet is the hinged cover over the engine of motor vehicles that allows access to the engine compartment for maintenance and repair. In British terminology, hood refers to a fabric cover over the passenger compartment of the car...
of an automobile
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
that either allows a flow of air to directly enter the engine compartment, or appears to do so. It has only one opening and is closed on all other sides. Its main function is to allow a direct flow of air to the engine, hence the need for it to be upraised so as to effectively channel air to the engine compartment. It may be closed, and thus purely decorative, or serve to enhance performance in several possible ways.
Cool air
One possible use of a hood manifold. In most modern automobiles, internal combustion engineInternal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
s "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 28°C (50°F) 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.
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 resonanceResonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
supercharging
Supercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
effect. Such effects are typically only felt at very high speeds, making ram air primarily useful for racing, not street performance.
Pontiac
Pontiac
Pontiac was an automobile brand that was established in 1926 as a companion make for General Motors' Oakland. Quickly overtaking its parent in popularity, it supplanted the Oakland brand entirely by 1933 and, for most of its life, became a companion make for Chevrolet. Pontiac was sold in the...
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 turbochargerTurbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
s or supercharger
Supercharger
A supercharger is an air compressor used for forced induction of an internal combustion engine.The greater mass flow-rate provides more oxygen to support combustion than would be available in a naturally aspirated engine, which allows more fuel to be burned and more work to be done per cycle,...
s 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
Intercooler
An intercooler , or charge air cooler, is an air-to-air or air-to-liquid heat exchange device used on turbocharged and supercharged internal combustion engines to improve their volumetric efficiency by increasing intake air charge density through nearly isobaric cooling, which removes...
(which is a heat exchanger similar to a radiator
Radiator
Radiators are heat exchangers used to transfer thermal energy from one medium to another for the purpose of cooling and heating. The majority of radiators are constructed to function in automobiles, buildings, and electronics...
) 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 cowlCowling
A cowling is the covering of a vehicle's engine, most often found on automobiles and aircraft.A cowling may be used:* for drag reduction* for engine cooling by directing airflow* as an air intake for jet engines* for decorative purposes...
, where the curvature of the windshield
Windshield
The windshield or windscreen of an aircraft, car, bus, motorbike or tram is the front window. Modern windshields are generally made of laminated safety glass, a type of treated glass, which consists of two curved sheets of glass with a plastic layer laminated between them for safety, and are glued...
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
Boundary layer
In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface where effects of viscosity of the fluid are considered in detail. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal...
(the slow-moving air that clings to the surface of a moving object) or if it is a "NACA duct
NACA duct
A NACA duct also sometimes called a NACA scoop or NACA Inlet, is a common form of low-drag air inlet design, originally developed by the U.S. National Advisory Committee for Aeronautics , the precursor to NASA, in 1945....
," 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.
Under the hood, an effective scoop must funnel air into the engine's intake in as short and direct a path as possible, preferably through a tube or channel that is insulated against underhood heat.
A scoop may be part of the hood, or may be part of the engine's air cleaner assembly, protruding through a hole cut into the bonnet. Such a scoop is called a shaker hood, because the scoop vibrates noticeably when the engine is running, especially under power.
Hood scoops and off-road racing
A hood scoop/top mounted intercooler can be beneficial, especially during an off-road rally race. Rocks and debrisRoad debris
Road debris, a form of road hazard, is debris on or off a road. Road debris includes substances, materials, and objects that are foreign to the normal roadway environment...
can be kicked up by a car in front, and those objects can damage a front mounted intercooler. However, rock guards can be installed to prevent this problem.