VTEC uses three cam lobes and three corresponding rocker arms for each pair of valves, these are all electronically controlled from the ECU (Engine Control Unit)
The VTEC system can alter not just valve lift, but valve timing as well in response to engine load and driver demand. VTEC operates on intake as well as exhaust valves. The ECU is setup to change to high lift cam profiles at a certain RPM (generally somewhere around 5000rpm, but depends on the model) While all this is happening another intake opens up in the manifold to enable more air into the mixture to fully exploit this different cam profile setup.
The result is a normal engine when driven sensibly, then a beast when you open it up and get the revs above 5000rpm
Since the VTEC system is electronically controlled, various settings can be changed from the ECU. Cam changeover point can be modified from a Plug in box like the VAFC from APEXI. Replacement race spec ECUs raise the rev point and modify fuelling and air flow parameters to fully exploit the VTEC engine
