The 928S4/GT and GTS oil scrubbing system is not perfect and causes inhalation of oil mist into the intake, which in turn causes pre-detonation and some serious oil consumption at higher rpm's.

Several solutions exist for help mend this. One is the modified breather connections which came standard at the 1993 model (see other page on this), use of a provent separator, and also modifications on the oil filler neck that has the function of separating oil.

Kuhn Performance makes this filler neck insert:

Oil scrubber Kuhn performance.pdf

Oil Scrubber System install.pdf

A discussion exists if the filling with Dish Pot Scrubbies is the best way to do.

I have one of these, and I removed the scrubbies so that only a louvre openings and sort of a small net inside exist. That may help the oil drip back into the pan.


After testing with three different 928 track cars (and a couple ZO6's) with various ideas for oil control, using copper scrubbies in the breather exit needs to be reconsidered.

It works great for short term quick bursts (like on a dyno pull) but beyond that not the best idea for two reasons:
1. The oil that was part of the vapor trying to exit the engine will collect in the scrubbie and start to migrate up the copper and exit the engine anyway. You've now gone from a fine oil mist to liquid now exiting the block. Not good.
2. Any kind of restriction is a bad thing, the more the copper gets soaked with oil, the harder it is for any crankcase pressure to exit the engine which increases crankcase pressure - also not good, especially with a boosted car that isn't tuned 100% which will experience high than stock levels of crankcase pressure.

The dish pot scrubbies work OK when used "downstream" from the crank opening (like in a separator) but still not a perfect solution.

IMO the two baffle plates from Roger or Carl that help direct the oil away from the opening without ever restricting the air flow is the best way to go. Also this one from 928 International: 107 707 05 (product does not exist anymore...) - is this the some one Roger sells? I cannot find it on the 928's R Us site.

Follow this with a good air / oil separator before piping back to the intake.

Many use the ProVent, but I prefer more of a cyclonic style or multi chamber separator.

Here are two proven designs for the VW / Audi turbo crowd. They simply plumb in between the breather opening in the engine and the line going back to the intake:

There are also the complete solutions like Greg Brown and Dave Roberts offer:



I agree with this, how the system is configured and what the baffle is expected to do is the right starting point for deciding what works the best. For my car, the best solution was a version of John's louvered box _without_ the scrubber inside. For my purposes, the louvered box is a superior baffle compared to the simpler baffles.


The flat plate I got from DEVEK made things worse. I'd go with one that drops down. The scrubbies wouldn't be good for extended or track use for the reasons given above.

The 16V engines have different problems in the heads as the designs are very different. I've got a home-made filter in the outlet from the oil filler with air returned to the filter box. That helps me gauge what's coming from the engine. There is no drain to the sump from the catch but a stopcock valve.

I suggest a baffle as pictured plus a catch can on the filler outlet. You can get a catch can cheaply or just make something.


I replaced a 928 intl style simple baffle with Gregs version shown above - helped incrementally - my vacuum pump still sucks oil out but less then before...

In this change I also removed an oil filler necks worth of copper scrubbies (beautifully clean after 2 years) but way too restrictive and still really didn't seem to reduce ejection that much (so maybe Eric is right).

For me Greg's baffle is better than the 4 filler neck scrubbies and the 928Intl baffle. These too were much better than nothing when I first installed them...


1994 928 GTS Black(741)/Black Manual "AZ Desert Sharks"


these are the ones Roger at 928sRus sells (made by Greg Brown):