Actually they both handle outflow. at idle on a engine in good condition the breather can allow what little additional air the PCV may pull to enter but that's about it.

It's a common misconception obviously that the PCV is some huge evacuation pump constantly pulling air out of the crankcase, it's not. at the time you have the most blowby ( crankcase pressure ) is at WOT, at this time you have no vacuum so the PCV is simply a 3/8" breather and your standard breather vents the rest. at high vacuum like idle the PCV limits the flow and it pulls most if not all the blowby into the intake. you can live with or without a PCV but you cannot keep seals in without a breather, so hooking a nose to it is a good idea when possible just to burn fumes.

If physics alone isn't enough look where your breather enters the air cleaner housing, see if it's squeaky clean or if it has any oil residue. on good engines there'll be little or no oil because the blowby is so minimal, on a worn engine it'll be gunky. on the factory air cleaner on my 440 six pack Challenger the hose from the breather is just placed close to an open element air filter. it offers no filtering whatsoever, but it places the blowby close enough to burn most of it. because Chrysler knew which way the flow is going.

 

Sorry to belabor this topic - should the breather (assuming I connect it to the air cleaner) also have a valve in it to limit the direction of flow? My PCV only allows flow in one direction - from the crankcase to the carb. Shouldn't the breather also limit flow direction from the air cleaner to the crankcase? From what I see, where are passive breathers with no flow direction limiter but also some with a PCV integrated. Which do I want? Thanks!

 

Your breather is intended to let air flow both ways. the valve in your PCV isn't there to limit the direction if flow it's there to limit vacuum draw . at idle it's pulling some vacuum at WOT it's allowing a little crankcase pressure to be pushed out.

You always need a breather, you should have a PCV . you never have just a PCV so don't think of the two as the same think of them as separate parts.

 

Very helpful. Thank you! I was envisioning it as PCV = OUT / Breather = IN.

 

Edelbrock makes an adapter (part number 1205) that attaches to the air cleaner baseplate so you can hook hose up from your breather directly to the base plate. That what I used on my air cleaner. As already stated, its good to allow filtered air into your engine and if there is any excess crankcase pressure at high rpms, the vapor goes back into the intake to be burned vs making a mess of your valve cover.... On my engine, hose goes from stock breather cap on valve cover to edelbrock adapter mounted on rear of baseplate. Works well.