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Hi,
VarioCam is Porsche's Variable Valve Timing System. There are two generations of it. The 1st was used on the M96 Engine from '97 - '02 and is operated by an Electrical Solenoid. The 2nd. Generation was introduced on the '03 Models and uses a Hydraulically spun stator.
There is Valve Overlap on every engine cycle, that is, there is a time in the cycle, at the end of the Exhaust Stroke and the beginning of the Intake Stroke where all the Valves are opened. Changing this overlap (duration) changes the way the Engine behaves and the Power/Torque it produces.
Greater Overlap enhances the amount of AF which the Cylinder can take in which results in higher Torque, but also higher Emissions. Lesser Overlap increases HP and reduces Emissions, especially at low throttle and idle.
In the past, a Camshaft was always a compromise between these variables. But, with Adaptive Valve Timing, the Overlap can be made to change according the Engine Speed.
To do this, the Cam is literally shifted, that is, the Lobes are either advanced or retarded. In the 1st Gen VarioCam, the DME signals the Solenoid which shifts the Cam at a pre-set Engine Speed. It is either On or Off and the Overlap is shifted a fixed number of degrees.
On the 2nd Gen VarioCam, the Engine Speed builds Hydraulic Pressure in the Stator corresponding to Engine Speed. Unlike the 1st Gen, this allows for infinitely variable Overlap within a 40 Degree radius of the Crankshaft - it is essentially always On. It has the added benefit of eliminating the Drive Chain between each pair of Camshafts, simplifying the design, making it more reliable and eliminating some weight. Hope this helps...
Happy Motoring!... Jim'99
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