Quote:
Originally Posted by KarlzEE Bebout
My manifold for my Webers does have a plenum chamber on the underside with two threaded pipe plugs in between the carbs. I don't know what brand it is and don't remember seeing a name. I put a 90° fitting in one of those, ran a hose with an inline PCV valve to a tee fitting with hoses going to both valve cover breathers. Works pretty well but I do still get some blow by with some higher RPM spirited driving. Might have something to do with the engine getting close to 90,000 miles  |
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.