Technical PCV valve orientation

Does a PCV valve need to be vertical to work right, or can they be on their side?

 

From 1963-67, small block Chevrolet V8s had a horizontal PCV valve that threaded into a fitting on the rear of the carburetor.

 

Worth 1000 words

 

These early PCV valves flow the opposite direction to rocker cover PCV valves.

 

Vertical and Horizontal use is not the same

The original GM p/n was 6422294 (item 5) ; this diagram is for a 283


NAPA CRB29255 is a replacement. It is a horizontal mounted PCV valve.
It is what I used on the 331 Hemi
It has a 1/4" NPT male thread and a 1/2" hose barb



From what I have read elsewhere, an AC DELCO CV590c is also a replacement for the GM valve.

 

They will work horizontally or vertically. However, you might experience a light fluttery rattle from them if vertical. I had one vertically screwed straight into the underside of a flatty manifold. It rattled. I took it out and using exactly the same pcv valve, fitted a 90 degree elbow to make it horizontal. It did not make a noise then. I showed it in one of my videos. Mart.

 

I have used this setup on many of my sbc with no issues or rattles. This is the way the L79, 350hp motors
came from the factory, as well as others.

 

1965 327/350 hp engines did not use a PC valve, it had a metered orifice on the carb.



1966/67 L79's (325/350) hp engines used this style.

 

Thanks for the information, I guess I don't really understand how they work inside, but I know what they do and why you use them.

 

Basically just a simple check valve to allow for one-way air movement only. If there was a backfire, it
prevents damage to attached hoses and equipment.

 

The V100 replacement is oriented to screw usually into a back of the carb. I use one on a YBlock and a GMC 6. Both use 90* angle fittings.

 

I think the question is too general. Most modern pcv valves work horizontaly ok as they are designed that way anyway BUT some early valves back when they were figuring stuff out had large weak springs and relied on the weight of the piston to regulate flow under vacuum conditions. So really you should orientate it as per the original application or get one thats designed to work how you fit it on your motor to make sure it operates correctly.

You also need very good oil separation of the breather with a drain back upstream of the valve otherwise you will get a very smoky motor.

 

That's the one I have in the valley pan of my Hemi.