VTEC (GS-R)
Variable Valve Timing & Lift Electronic Control System (VTEC) uses 3 different intake cam lobes and rocker arms, synchronizer pistons, and a VTEC solenoid valve. See Fig 1 . The 2 low lift cam lobes operate primary and secondary (outer) rocker arms. The high lift cam lobe operates the connecting (middle) rocker arm. The PCM controls VTEC solenoid valve which in turn operates synchronizer pistons. See Fig 1 .
At low speed, primary and secondary rocker arms control intake valve timing, lift, and duration. The connecting (middle) rocker arm remains disengaged, and has no effect on engine operation. At high RPM with heavy engine load, the PCM activates the VTEC solenoid valve to apply oil pressure to the synchronizer pistons located in primary and secondary rocker arms. This locks primary, connecting, and secondary rocker arms together so they are driven as a single unit by the high lift cam lobe which the connecting rocker rides on.