Integra 1.7L
VTEC uses 3 different intake cam lobes and rocker arms, synchronizer pistons, and a spool valve. See Fig 1 . Low lift cam lobes operate primary and secondary (outer) rocker arms. High lift cam lobe operates connecting (middle) rocker arm. PCM controls spool valve and synchronizer pistons.
At low speed, primary and secondary rocker arms control intake valve timing, lift and duration. Connecting rocker arm remains disengaged and has no effect on engine operation. At high RPM with heavy engine load, PCM activates spool valve and oil pressure is applied to 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 high lift cam lobe.