Reply to "To PCV or Not to PCV??"

Ron,

yes, the pcv valve is a check valve. it closes during periods of high intake manifold vacuum, such as at idle or during deceleration. a "stuck" pcv valve will cause an erratic idle.

a pcv system should have a pcv valve on one rocker cover, plumbed to the intake manifold or source of vacuum, where vapor is drawn out of the crankcase. the other rocker cover should have a filtered source of fresh air, where air is allowed to flow into the crankcase, to replace the air removed through the pcv valve.

the dual filters you see on some "hot rodded" engines, do not comprise a pcv system, they are just filters to filter any air that may decide to flow into the crankcase. with dual filters, the crankcase is simply being vented to atmosphere, preventing a build up of pressure in the crankcase, which would oppose the movement of the pistons & inhibit power production. there is no force being applied to positively vent the crankcase of vapors. when a long duration camshaft is installed in an engine (you know, the kind that makes a lumpy idle), the intake manifold vacuum at idle is so low that a pcv valve would stay open & therefore can't be used.

which reminds me of another story ...

George