An airbox is an empty chamber on the inlet of most combustion engines. It collects air from outside and feeds it to the intake hoses of each cylinder. Older engines drew air directly from the surroundings into each individual

carburetor A carburetor (also spelled carburettor) is a device used by an internal combustion engine to control and mix air and fuel entering the engine. The primary method of adding fuel to the intake air is through the venturi tube in the main meteri ...

. Modern engines instead draw air into an airbox, which is connected by individual hoses to each carburetor or directly to the intake ports in fuel-injected engines, thus avoiding an extra intake manifold. The airbox allows the use of one

air filter A particulate air filter is a device composed of fibrous, or porous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. Filters containing an adsorbent or catalyst such as charcoal (carbon) may als ...

instead of multiples, reducing complexity. Developments arising from concerns about engine emissions during the late 1970s allow the airbox to collect pump gases from the crankcase and the tank air vent and re-feed them to the engine.

Developments

Since the 1990s, engine designers also sought to exploit the properties of oscillating gas to improve performance. Many high-performance

motorcycle A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruising ...

s have the airbox fed from funnels in the front of the bike, where increased pressure forces more air into the intake and thus improves power. Examples for this

ram-air intake A ram-air intake is any intake design which uses the dynamic air pressure created by vehicle motion, or ram pressure, to increase the static air pressure inside of the intake manifold on an internal combustion engine, thus allowing a greater massf ...

construction are the SRAD models of the

Suzuki GSX-R750 The Suzuki GSX-R750 is a sports motorcycle made by Suzuki. It was introduced at the Cologne Motorcycle Show in October 1984 as a motorcycle of the GSX-R series. Air and oil cooled The air and oil-cooled models can be divided into the first-g ...

, the

Kawasaki Ninja ZX-6R The Kawasaki Ninja ZX-6R is a ''636 cc'' class motorcycle in the Ninja sport bike series from the Japanese manufacturer Kawasaki. It was introduced in 1995, and has been constantly updated throughout the years in response to new products ...

or the BMW S1000RR. Secondly, designers exploit a property of air cavities known as

Helmholtz resonance Helmholtz resonance or wind throb is the phenomenon of air resonance in a cavity, such as when one blows across the top of an empty bottle. The name comes from a device created in the 1850s by Hermann von Helmholtz, the ''Helmholtz resonator'', wh ...

. Flow through the airbox is optimal at its

resonance frequency Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillat ...

, which depends on airbox volume and the inlet area and length of the snorkel. The resonance is typically chosen to be at a medium speed where torque otherwise drops, caused by

valve timing In a piston engine, the valve timing is the precise timing of the opening and closing of the valves. In an internal combustion engine those are usually poppet valves and in a steam engine they are usually slide valves or piston valves. Internal ...

overlap.Resonant airboxes: Theory and Applications
Mark Lawrence, requested February 5, 2016

References

Engine fuel system technology {{motorcycle-stub