A variable air intake uses valves to vary the length of the intake tract (the path incoming air takes into the combustion chamber) in order to optimize power and torque over the entire engine-speed range.

Primary Benefit:

Depending on engine speed, intake manifolds of different length are advantageous - at low engine speeds a longer runner increases torque and improves responsiveness, while at higher speeds the shorter runner is effective for high performance. By varying the length of the intake tract, power and torque are optimized over the entire engine speed range.