PCV Valve Or Breather

[mikester]

Leaks are secondary. Cylinder seal is the primary reason for PCV.

Race cars run open breathers because of frequent rebuilds and the bulk of the time is at WOT. But street cruisers should adopt the exact opposite mentality.

If you intend to put a fair amount of street miles on your car, then a PCV is a must S well as a proper breather. Both work in unison.

Got the breather on the other side. Have the PCV already but the fitting on the manifold is making it tight to get to the barb on the back of the Holley. The other issue Im working on this week is the vacuum or lack of it for the booster. Looking at vane pumps but now Im not sure if I'll have enough manifold vac for the TH400 modulator.

 

[ck80]

Thanks for your response 64. This car is my 87 El Camino and will live on street with only the "heavy foot" WOT experience for sheer enjoyment to impress others! As a retiree, there will be some daily driving and going to local cruz nights here in the islands. I can address acid buildup due to moisture with more frequent oil changes. However, I am concerned about crankcase pressure resulting in oil pan and timing cover leaks since changing gaskets in these areas are a pain in the butt. As many of us envision, we see our kids enjoying these vintage vehicles once we leave the scene.

You're close, but a little off in at least how you're writing out your thinking. See if this helps:

Either the breather or the pcv will release the excessive pressure. Example - it's like saying left spigot or right spigot release water out the faucet.

Breather is passive, like an open window. It'll let excess pressure out, but that's it. Without some outside force (wind, fan, etc) it does nothing to actively purge the existing air in the room.

The PCV works by actively having that outside force to purge the existing air in your crankcase, usually drawing some vacuum to suck the air out through the valve. The PCV purpose isn't explicitly designed just around moisture removal, but to extract all those lingering suspended vapors that may be present (hydrocarbons? Moisture? ANY vapor suspended in the extracted air) from inside the crankcase and allow that removed air with any suspended vapors to be reintroduced through your induction system for burning in the combustion chamber.

If you ran breather only you wouldnt purge out those vapors, at least not beyond any that were carried out incidentally by vented pressure. Theyd sit there, increase in concentration, and as vapor concentration reaches a critical mass it settles increasingly on surfaces that the heavily laden air touches, or, has more compounds available to combine with suspended water molecules and make acidic compounds, sludges, deposits, etc, so on so forth.

So, breather is an open window on a windless day. Pcv is a box fan in the window.

Edit: or better example...

Go eat a bunch of Mexican. Use the restroom. Open the door (breather). Turn on ceiling fan (PCV).

One eliminates the noxious gases and substances from the air better than the other. Except combustion isn't a one time use like you in the restroom, its constant use. You can see how active venting (PCV) makes a difference.

 

[spidereyes455]

Back before the days of PCV valves cars used a breather and a road draft tube. It was literally just a tube from the crank case that ran to the underside of the car where air passing underneath the car would create a suction/siphon effect to purge crankcase vapors. The drawback was it only worked when the car was moving at a sufficient speed and would deposit all the oil vapors on the road surface and the underside of the car. Thats why old pictures of highways from the 50's and 60's have so much oil on the road surfaces.

 

[mikester]

Ths is what Ive got at idle. When I bought the cam the tech at Comp Cams said I was right at the edge of having enough vac for power brakes. Guess he was off by a little. LOL

 

[57 Handyman]

Thanks Mikester, that's what I was looking for. Now, I see it is not significant. Also, based on ck80's remarks, I understand things a bit more.