VVTi stands for Variable Valve Timing with intelligence, a system introduced by Toyota in 1996 to replace the previous VVT one.
To understand the need for a variable valve timing system, you first have to know that in a normal engine, the relationship between inlet and exhaust valves opening and closing is non-adjustable, because they depend on the direct connection with the camshafts.
This means that the fuel is wasted, higher levels of exhaust emissions are produced and the power output potential is not fully realized. All these problems can be solved by allowing the intake valve to open slightly before the exhaust valve closes, thus increasing the time for the fuel/air mixture to enter the cylinder during the intake stroke. This phenomenon is also called “valve overlap.”
The VVTi solves all the problems by using a computer and special camshafts to allow the relationship between the separate inlet and exhaust one to vary the valve timing overlap.
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