Developed by Harley-Davidson Motor Co. to reduce sound and noise emissions produced by their line of motorcycles, the Active Intake Control (AIC) system is an electronically controlled servo that opens and closes a valve in the intake chamber according to preset engine speeds. The Active Intake Control works together with the Active Exhaust Control system.
Working in accordance to meet higher emissions standards introduced by the European Commission and the Association des Constructeurs Europeens de Motocycles (ACEM) in 2008, Harley-Davidson began to implement the Active Intake Control and the Active Exhaust Control systems in their international motorcycle models.
The purpose of the Active Intake System (AIS) is to lower the amount of sound, or noise, emitted by the motorcycle by regulating the intake of air into the motor. The AIS is composed of a valve and a servo that is controlled by the motorcycle's Electronic Control Module (ECM).
At idle, the AIS valve is closed, restricting the amount of air allowed into the motor to a minimum and lowering the sound levels of the exhaust. As the engine speed increases, the ECM sends a signal to the servo, which opens the valve and allows more air into the motor to meet the required air/fuel ratio for higher performance demands.
Harley-Davidson's motorcycles have benefited from the introduction of the AIC system, in conjunction with the Active Exhaust Control system, by reducing the amount of audible and gaseous emissions to create a more environmentally sound source of transportation.
Bypassing the AIC
Although most motorcyclists may not notice the presence of the Active Intake Control, many performance-minded riders have noted that the restrictive intake may rob the motor of power. To combat this, the AIC may be bypassed with aftermarket "emulators." Doing so, however, will void the manufacturer's warranty and is intended only for off-road riding.