Quote:
Originally Posted by amondc
Anything is possible. All I can speak to is what I found on this particular car.
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I am an engineer, electrical, admittedly, but the approach is the same. I have no business connection with PedrosGarage, TuneRS etc. I do know some of the individuals and therefore know some history of the testing and results, which is why i know this is not normal at all. In fact i wish i had two DOFs rather than the two (otherwise) excellent bearings i do have.
This quoted statement is very true. The OP can only speak to the car he saw. With the facts given, there is little one ca say about the DOF.
let's look at the issue. He is claiming that the DOF draws sufficient oil to lower the oil pressure/flow. He leaves unsaid the implied mechanism of starving the Variocam.
What we do know is that:
1. on many, many cars with DOF there is no problem - so a healthy engine can certainly suffer the small DOF losses (think of it a parallel resistance in the load)
2. Porsche must design with a variety of flow rates in mind, from idle to 7k rpm. Oil pump volume will vary greatly. It cannot be terribly sensitive to a small load change
3. the draw is 100ml< draw < 400ml - vastly below the available oil flow
We also know that many things affect available oil flow: pump condition, oil passage condition (blockages, sludge etc.) debris.
This can be modeled as the fluid dynamics version of an impedance match. If you have a hgih impedance (low flow) source, a moderate load will cause a drop in voltage (pressure, and, by extension, flow) in both the parasitic flow (DOF) and the main flow (heads/variocam). This in fact could have been measured if the mechanic wanted to understand the cause. Maybe it shoudl be.
The cause - to me - is very likely a motor that is already flowing poorly. The why is hard to say, but sludge or blocking debris would be high on my list to investigate.
Oddly, the DOF may have been an early warning system for a much more serious problem - automotive arterial sclerosis.
We don;t know, but speculation should be used productively and this seems to be not only jumping to conclusions, but very likely the wrong one.
Just_Me