Random musings on the variocam system -
Activation of the system adds 25 deg timing to intake valves, effectively reducing valve overlap
Idle - system is inactive, valve overlap is significant. But why? Overlap at idle causes a lumpy sensation
1300 rpm - system is activated. Overlap is decreased. let's make some power!
Reduced valve overlap continues through low rpm range - this is bueno. Better charging of cylinders because of scavenging and low intake air flow velocities.
But then we stay with reduced overlap until 5500 rpm? This confuses me. I have no real world experience with tuning but this seems rather high. Torque curve for both the 2.7 and 3.2 are already on the way down by this point, who not kick back sooner?
Above 5500 rpm, back to increased valve overlap, thus increasing volumetric efficiency (theoretically) and smiles per gallon. Shortly after this though, torque output tanks.
As all random musings do, this one end with questions.
First - has anyone played with the timing of activating / deactivating variocam? It seems that a more logical place to revert back to increased overlap is closer to 4.5k rpm.
Second - does this system actually work? On the 2.7 chart, torque stabilizes at deactivation but only for 800 rpm and then falls. On the 3.2 it holds in place for even less range and then plummets. If the goal of the system is to maximize power output, but it could contribute to less than smooth idle and doesn't rescue the output curves when deactivated, what exactly are we doing here?
Third - has anyone ever dyno'd with and without variocam system operational? Even better - with variocam continuously activated? And maybe just deactivated early?
Musings over. Looking forward to replies.
Best,
Ike
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