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Published on May 20, 2010
This is an extremely important video taken by Louie Ott of the interior of the cam cover of a Porsche 928 on a track back in 2003.
www.performance928.com is Louie's website.
In hard left turns the oil can be seen to be violently blasted up the oil return passages -- one of which would be to the left of the tappet. There is a delay that is approximately 5 seconds long (give or take) and the aerated oil in the shallow area of the sump and probably that oil which has drained down from heads makes its way to the sump. The highly aerated oil is drawn into the pickup tube and compressed by the pump. Typically oil can hold dissolved air at about 9% per bar pressure. The Porsche pump runs at many bars of pressure. When the oil emerges from the cam bearings (primarily) it releases air from the supersaturated oil like sodawater and this whitish-brown foam is clearly seen to be flung by the cam lobe onto the plexi-glas window.
This is direct evidence of the high aeration of the oil in the wet-sumped 928 engine in competition use. This high level of aeration is what kills the 2/6 bearings. They just happen to be the first to get a good sustained dose of it in these situations. The Porsche 944 engine has a similar failure mode for the number 2 bearing since the bed plate oil passages are arranged similarly. The 944 engine was derived from the V8 block in the 928.
This video is left unedited so that people can see the raw data.
Louie's description and commentary can be found here: