B18C1 Engine
VTEC uses 3 different intake cam lobes and rocker arms, synchronizer pistons, and a spool valve. See Fig 1 . The 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 spool valve and synchronizer pistons.
At low speed, primary and secondary rocker arms control intake valve timing, lift, and duration. The connecting rocker arm remains disengaged, and has no effect on engine operation. At high RPM with heavy engine load, the PCM activates the spool 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.