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Old 11-09-2011, 08:53 AM   #23 (permalink)
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The source of the air flow won't change the mixture ratio. I can't see the mileage claims from changing the PCV flow. Crankcase blow by, the source of pressure increases as the engine slowly wears and ring leakage increases. mwebb's idea of a balloon over the dipstick tube shows there is no more blow by to bring into the manifold in a properly operating system unless ring leakage is excessive. Maybe they were comparing it to a malfunctioning PCV system where the excess blow by would push oil past the rings.

The difference in pumping losses can not account for the claims of increased mileage. Actually increased EGR flow provides additional combustion chamber pressure without additional fuel, since the oxygen content in the exhaust gases is low. Maybe they rationalise that the unburned fuel in the blowby would be consumed on the extra trip through the cylinder. If you were loosing 20% of your fuel that way, you would have some badly diluted oil and an engine on it's last gasp.

I know in the old MB sedans in the early 80s a vacuum leak in the central locking system would allow the engine to run on the air passing through a 1.5 MM ID vacuum line in one of the doors. In 82 they eliminated the throttle butterfly in all of their diesels and claimed a 7% increase in efficiency from eliminating all manifold vacuum completely.