Pcv Valve

[Finallygotmine]

Ok, stupid question: is not a PCV valve suppose to conrol the air drawn from the crankcase?
I just picked up a new PCV valve from NAPA, and I can suck air through it like a straw. How is the manifold suppose to develop vacuum at idle if it can easily pull air in from the crankcase? Is it not supposed to be spring loaded to resrtict the air?

 

['67 Charger Kid]

I'm pretty sure that's completely normal, I believe they are bad when you can't suck air through them.

 

[70rr-brian]

Does the PCV rattle when you shake it? If so you are probably OK.

When you are at idle/cruise the engine produces enough vacuum (assuming you don't have some mega cam) through the carb to suck the crankcase pressure out through the PCV. It does so by lifting the valve so air/crankcase gases can pass through it. When you are at WOT there is not vacuum and gravity takes over and the valve drops back down closing it off.

In theory, on a stock motor then the breather takes over where the PCV leaves off by sucking crankcase pressure in through the air cleaner and the crankcase gases are recycled through the carb in the form of "air".

 

[Ron 73]

An internal restrictor (generally a cone or ball) is held in "normal" (engine off, zero vacuum) position with a light spring, exposing the full size of the PCV opening to the intake manifold. With the engine running, the tapered end of the cone is drawn towards the opening in the PCV valve by manifold vacuum, restricting the opening proportionate to the level of engine vacuum vs. spring tension.

 

[Finallygotmine]

Yeah it does rattle. As far as cam, I don't know what is considered "radical" I did find out from previous owner that it has a 509 purple in it. could that cam, coupled with cam timing be giving me VERY low idle vacuum? I mean less than 3 inches at 7-900 rpm?
I took off the hose from the PCV and plugged the hole in the manifold. no change/very little, in vacuum

 

[70rr-brian]

less than 3" is VERY low. I assume you have a vacuum gauge then. The lift on that cam if memory serves is only like .509 (hence the name LOL)... I run a .582 lift cam and pull 12" of vacuum. I suspect you have other issues. Perhaps a vacuum leak and/or the timing/air fuel mix is out of whack. Running electronic ignition or old points? What is your timing set at?

 

[Finallygotmine]

I did find a major leak ops: My bad. I'm only pulling about 6-7 inches but it's running fine now. I just put Mass flo fuel injection in it. Initial timing is about 15-16. She rips now, Thanks to all for all the help.
Now I have to put in a new gas tank sending unit gasket. Leaked a little when I filled up.