VTEC System (J37A4 engine)

The VTEC system changes the cam profile to correspond to 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.
Both the intake valve side and the exhaust valve side have primary and secondary rocker arms. These rocker arms are locked and separated to change the cam profile by switching the oil passages. Roller rockers are used to minimize mechanical friction.

Fig 1: Identifying VTEC System (J37A4 Engine) Cam Profile
Courtesy of AMERICAN HONDA MOTOR CO., INC.

Fig 2: Identifying Roller Rockers
Courtesy of AMERICAN HONDA MOTOR CO., INC.
The VTEC system oil pressure switched by the rocker arm oil control valve changing the hydraulic circuit. The rocker arm oil control valve is controlled by the rocker arm oil control solenoid. The rocker arm oil pressure switch detects VTEC system oil pressure and sends this information to the ECM/PCM.

ENGINE SPEED	ROCKER ARM OIL CONTROL SOLENOID	INTAKE and EXHAUST VALVE LIFT
LOW	OFF	LOW
HIGH	ON	HIGH