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Old 08-19-2005, 07:28 AM
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PVC valve on SBC 1970ish location question

Mine is tapped directly into the intake manifold.
I just saw one that was piped into the air cleaner
housing (above the throttle blades). What are the
pros and con's of each setup?

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Old 08-19-2005, 08:12 AM
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PCv Valve

A PCV valve requires Vacuum to operate. They are either piped to a vacuum port on the manifold or on the carb. What you see going to the air filter is just a breather. Usually there is a little foam element in the air cleaner to keep all the nasty suff from cloging up your filter. There should be a PCV valve elsewhere also.
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Old 08-19-2005, 08:36 AM
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The PCV system is a closed system. One hose goes from the air cleaner to one of the valve covers. The other valve cover has the PCV valve in it with a hose going to a vacuum source(like yours). When the engine is idling vacuum is high and will draw any fumes out of the engine which will cause the crankcase to draw in clean air from the air cleaner hose. When the engine is revved up manifold vacuum drops to almost nothing so the PCV valve's internal spring closes and does not draw in any air. If the crankcase becomes "pressurized" from too much blow by from the cylinders that is when you will see the breather filter in the air cleaner become clogged with oily vapors which will then catch even more dirt from the air coming into the air cleaner.

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