The mechanics of the DOHC VTEC valvetrain in the B18C* and H22* are fundametally identical. On VTEC valvetrains, oil pressure is used to drive locking pins out from the center rocker arm, which locks it to the two rocker arms that acutally bear down on the valve/ spring assembly. As a result, the valves are now opened as dictated by the center cam lobe, which is ground for high-rpm performance (higher lift, longer duration). This switch takes place at around 5500rpm, though it depends on engine load, throttle position, knock sensor activity, etc.

Starting with the K-Series, the new i-VTEC systems introduce a hydraulically controlled system to vary the camshaft position relative to the cam sprocket (Honda calls is VTC if memory serves). This is an independent system that complements the VTEC valvetrain system mentioned above.

One application of this technology is to leave the exhaust valves open a scoshe during the intake cycle, thereby eliminating the need for a conventional EGR (Exhaust Gas Recirculation) valve. Depending on application, VTC will also advance the intake cam (at low-rpm, I think) to aid cylinder filling on the intake stroke.

Those are the major differences as I remember them.

Oh, and moved to Engine Tech. h: