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 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

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 BMW S1000RR is a race oriented sport bike initially made by BMW Motorrad to compete in the 2009 Superbike World Championship, that is now in commercial production. It was introduced in Munich in April 2008, and is powered by a four-cylinder eng ...

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

References

Engine fuel system technology {{motorcycle-stub