Quote:
Originally Posted by Tommy
Perhaps I don't understand your description, but it sounds like the vacuum from your plenum is pulling through the PCV valve to two breathers. If so, it seems to me that at higher vacuum levels the plenum is likely pulling in outside air more than crankcase vapors. I used the more common arrangement of having the PCV pull from one valve cover with the breather on the other. At low RPM / high vacuum the system pulls crankcase vapors in through the PCV valve while outside air enters through the breather to equalize the pressure. At high RPM with high crankcase pressures, the PCV pulls in as much as it can and excess pressure is vented out through the one breather.
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I didn’t stay at a Holiday Inn Express last night but that’s how I’ve always understood it too. The PCV valve allows vapor flow from the high pressure (valve cover/engine crankcase side) to the low pressure (intake/vac source side). I don’t think the PCV valve totally shuts off flow, it just regulates it. Low RPM/high vacuum pulls the PCV valve disc up, against spring pressure, and restricts gas flow through the valve body. When vacuum reduces during higher RPM, the valve body spring pressure overcomes the vacuum source and pushes the valve disc back down to allow more flow through the valve body and into the vacuum source. Of course these crankcase vapors would flow much better with some sort of ventilation, and like Tommy pointed out, that is usually done on the opposite valve cover via a vent.