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Originally Posted by SD987
Variocam was developed for the 968 in 1991. It used a timing chain to vary the phase angle of the camshaft, thus providing 3-stage variable valve timing. The 996 and Boxster use a similar system. This design is actually inferior to the hydraulic actuator used by other car makers (such as VTEC in your original question) since it doesn’t allow as much variation to phase angle.
I believe what MNBoxster refers to as the "2nd Gen Variocam" is known in Porsche-speak as Variocam Plus which was introduced with the 996 - 911 Turbo and is standard on the 997. "Plus" uses the hydraulic actuator instead of a timing-chain and provides continuous (infinite) variable valve timing. More importantly, as 986Jim notes, the "Plus" adds variable valve lift.
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Hi,
No disagreement, except that the VarioCam is Solenoid actuated and not 3-stage. It uses a change in tension of the Timing Chain (actually the Camshaft Drive Chain) to affect the phase shift. This tension is varied by an Electronic Solenoid. It effects only a change in Overlap.
VarioCam Plus
is the 2nd Gen of the system. It uses Engine Speed - dependent Hydraulic Pressure to perform the Phase Shift continuously, eliminating the Chain and Tensioning components. Also, the VarioCam Plus Camshafts differ in that they have two sets of lobes, with different profiles, for each Valve - similar to Honda's VTEC system.
Additionally, the Hydraulic Lifters (Tappets) are 2-stage as well with two-stage lift on the Intake Valves. The two-stage Valve Lift function is performed by Electro-Hydraulically operated
switchable Tappets. Each of these 12 Tappets consists of Concentric Lifters, which can be locked together by means of a pin. The inner Lifter is actuated by a Small Cam Lobe, while the outer ring element is moved by a pair of larger-profile Lobes. All of this is initiated and synchronized by the DME.
In addition to the Engine Performance gains, weight was reduced by eliminating the Drive Chain and increasing MPG. The MPG improvement was sufficient to reduce the capacity, and therefore size/weight) of the Fuel Tank and still achieve the same range for the Car...
Happy Motoring!... Jim'99