How VarioCam and VarioCamPlus works - A Primer
 

Thought some of you might be interested in this write-up I found on Engine Management Systems, specifically the Cam Timing Control. It is a pretty thorough explanation of how the two systems, VarioCam and VarioCamPlus work. I also shows why upgrading from a 3.4/VarioCam engine to a 3.6/VarioCamPlus engine is not as simple as some might think.

The VarioCam system is a pretty simple on/off setup. The exhaust cam position is fixed relative to the crank, and the intake cam position moves a fixed 24 degrees relative to the exhaust cam. Note that the diagram shown is for the 1-3 head. The movement of the tensioner is reversed for the 4-6 head. At approx 1,500 rpm the cam solenoid/tensioner moves to advance the intake cam, and at 5,500 rpm it returns to the original position. I assume that the advance also takes place as rpm's fall. So the VarioCam systems is relatively simple.

With the VarioCamPlus system the amount of the movement of the intake cam relative to the exhaust cam is variable based on engine load, etc. And the exhaust tappets also adjust hydraulically to vary the valve lift from 3mm to 10mm. This is a much more sophisticated system.

What this shows is that the 7.2 DME that is used with a 3.4 engine has a simple on/off function for the VarioCam function. The 7.8 DME has a much more complicated function to adjust both the variable intake cam position and the exhaust valve lift. So there really is no way for the 7.2 DME to properly control the VarioCamPlus system. When I was researching the upgrade from 3.4 to 3.6 some sources said that they added a rpm based switch to the 7.1 DME to control the VarioCamPlus, but you can see that this really won't do the job properly. You would need to put a 7.8 DME in the car to get it to work.

Just some interesting info for those of use getting more involved with the complexities of our engines. Let me know what you think.

That's the most thorough explanation I have seen. Thank's for posting.

Thanks for posting this. Great explanation.

+100 Thanks!

V-tec baby! Thanks for the post...

Old thread but valuable information. I'm curious if with the engine at operating temperature you can heard the lifters?

Thanks op, good informative info....

Yup, Honda in 1989'. Wonder who was first, Porsche or Honda... What was the first vcam Porsche..?

One correction, Vario cam plus adjusts the lift of the intake cam, not the exhaust cam. I have never heard the lifters on any of my engines.

Mark is correct, the exhaust cam timing and lift are fixed on all Porsche engines from m96/7 and back, the first Variocam was the 968 engine in 1991...