[Dimi]

Hi Bill

OK Hear it is direct from Dr Porsche himself.

The certified oil for the porsche box is Mobilube SHC fully synthetic 75w-95 transmission oil as required for warranty on porsche boxes.

The factory fluid quantity for a porsche transmission in normal orientation is
3 Litres standard and 3.5 Litres with oil cooler.

The above is from the official Porsche factory workshop manual.

In the normal orientation the crown gear and shift forks are immersed in oil and due to the rotation of the gearsets the oil is thrown in a specific direction to effectively lubricate required parts.

In the inverted situation these gearsets etc are now out of the oil pool and are relying only on the thrown oil for lubrication and as the oil is now being thrown by the opposite gearset it is now also being thrown in a different direction to which it was originally intended providing a different amount and path to the areas that require lubrication.

To compensate a greater amount of oil in the box would be beneficial but just how much is not known.

Given that at any one moment in time while the car is being driven and the gearsets are turning a substantial amount of the total oil in the box will not be at the bottom of the box but in motion either flying around in the space in the box or running down the sides of the box there would be no detrimental effects unless the box were totally overfilled.

The unofficial estimates and opinions suggest up to a third of the available space in the box could be filled with oil without any detrimental effects after that the gearsets would be trying to turn while totally permanently submerged which could create problems such as overheating, frothing,etc.

Due to the gearbox being inverted when draining the oil very little would remain in the box as the lowest point in the box is now at the top and this allows the box to fully drain so the amount of oil that is put into the box should be exactly what comes out allowing accurate measurement of oil quantities.

The measured amounts done on my gearbox with the sight tube now gives us some very accurate reference points to work with and it leaves it up to us to do whatever we are comfortable with.

No one from any official Porsche source would be drawn to comment as what we are doing with these boxes is not a condoned use of the box or what it was designed for.

The thoughts and opinions expressed above are from several qualified and highly experienced Porsche factory mechanics that I managed to talk to and as close to an official answer that we could expect to get.

Some food for thought.
Dimi