VTEC (which stands for Variable Valve Timing and Lift Electronic Control) is an electronic and mechanical system in some Honda engines that allows the engine to effectively have multiple camshafts ( generally two ).
As the engine moves into different rpm ranges ( i.e :– either very slow or very high ), the engine’s electric control unit ( ECU ) can activate alternate lobes by attaching these lobes with the lobes which are controlling the opening and closing of the inlet and exhaust valves with the help of a pin which moves forward and backward parallel to the camshaft on the camshaft and change the cam’s timing.
In this way, the engine gets the best features of low-speed and high-speed camshafts in the same engine.
The alternate lobe is basically present between the controlling lobes and is bigger in size as compared to the controlling lobes.
And it also allows more air/fuel to enter into the combustion
chamber , that’s why it is only activated when the speed of the engine is very high.