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JFairman JFairman is offline
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Join Date: Jul 2006
Location: S. Florida
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On most normally aspirated cars the crankcase is plumbed into the intake manifold.
Kind of like "positive crankcase ventilation" pcv valve of the seventies.
It reduces blowby emissions by recirculating them and puts the crankcase into a slight vacuum so there are lower pumping losses in there and fewer oil seal leaks.

When you removed the oil cap it was like a big vacuum leak as air was drawn into the intake through the oil cap. The motor was running leaner so CO was reduced.

Some older BMW's will stall out or nearly die if you pull up the dipstick at idle speed for the same reason. I don't know if the newer ones are still like that.

Can't set up a 930 that way because you'd be presurizing the crankcase on acceleration.
Old 04-13-2010, 07:27 PM
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