Oops, why didn’t I realize this was in the manual? I’ll scope out my shop manual when I get home for more detail, but at a glance, it looks like the PCV valve on a ‘61 is plumbed into an “exhaust tube” the road-draft spot on the block (the “crankcase outlet” in figure 20), but the valve itself is way up by the carburetor rather than down on the crankcase outlet as I had envisioned. Thus, the exhaust tube acts as the baffle that prevents too much oil from being sucked out of the crankcase.
The later style is considerably simpler, though, I must say. You can tell the early system was a stopgap response to the change in emissions laws in California and the voluntary changeover adopted the next year by the AMA.
Chad, to answer your question, all crankcases are pressurized. If you don’t vent it, the pressure will find its way out through a gasket, with an accompanying oil leak. Early cars (pre-1961) typically used a road-draft tube that used the venturi effect to siphon blow by out of the crank case when the car was in motion. In 1961 California mandated a more enclosed system, and in 1962 the industry adopted the Positive Crankcase Ventilation system voluntarily because in reality, it’s a better system than the road draft tube: It’s cleaner and it does a better job of evacuating the pressure.
I say a “more enclosed” system, because fresh air is still drawn in from a breather somewhere, and sometimes oil mist and blow by will escape from there. Later in the ‘60s California mandated that the fresh air intake be routed through a filter element in the air cleaner to further enclose the system.
As far as not reducing pressure, I don’t fully understand how it works, but I do know that’s why there’s a spring-loaded valve and not just an open hose.
-Dave
