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PVC valve is more of an emissions thing i.e. positive crankcase ventilation.
It controls the amount of crankcase vapors that get sent to the induction system to be burned during normal running rather than expelled into the air. When it fails it sucks more than it should resulting in excess oil vapors being burned, thus smoke in the exhaust.
Pre 1960 there was just a tube in the rocker cover that let the vapors just go into the air just below the engine.
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