Integra 1.7L
VTEC utilizes 3 different intake cam lobes and rocker arms, synchronizer pistons and a spool valve. See Fig 1 . The primary and secondary (outer) rocker arms are operated by low lift cam lobes. The connecting (middle) rocker arm is operated by a high lift cam lobe. The spool valve and synchronizer pistons are controlled by the ECU.
At low speed, the primary and secondary rocker arms control intake valve timing and lift duration while the connecting rocker remains disengaged and has no effect on engine operation. At high RPM with heavy engine load, ECU 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 the higher lift duration cam lobe that operates the connecting rocker arm.