VTEC system

The VTEC system changes the cam profile to correspond to the engine speed. It maximizes torque at low engine speed and output at high engine speed.
The low lift cam is used at low engine speeds, and the high lift cam is used at high engine speeds.

Fig 1: Identifying VTEC System (Low Speed Valve Timing)
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Fig 2: Identifying VTEC System (High Speed Valve Timing)
Courtesy of AMERICAN HONDA MOTOR CO., INC.