PCV valve

OK I understand the need for a PCV system. But what is the purpose of the PCV valve? I went down to the local parts store and bought 2 differant valves with threaded (NPT) on one end.

Valve #1 From a 65 vette : Is open under ambient conditions, As vacuum increases the valve closes.

Valve #2 I have know idea as to its application: Is closed under ambient conditions, As vacuum increases the valve opens.

Is the purpose of the PCV valve to Open or Close the system under increased vacuum

 

There are both open and closed PCV systems. You may need to select your valve accordingly. If it's a more serious performance application, you may just want to run dual breathers and be done with it.

 

The valve controls when and amount of vacuum on the crankcase. Depending on what and how your mill is run will dictate what kind of valve you need to control crankcase pressures.

 

On a open PCV system what would be best valve to use? I am converting my olds engine to a PCV in place of the down draft tube assembly. Also should I restrict the amount of air which could be pulled through my breather?

 

they appear to work opposite from each other...but they do not.. 1 was designed to thread into the base of the carb( air flow from the barb to the threaded end) the other was designed to thread into the oil filler tube( air flow from the threaded end to the barb)..
the only time a pcv valve should close is during a backfire in the intake...also , be sure however you plumb it to make sure you filter the incoming air...another thing to be careful with is vent 1 side and pcv the other( or vent front and pcv rear) depending on the year..to completly vent the motor...no pcv/vent on the same valve cover...
good luck
dave ;-)