2 breathers vs PCV on rebuilt motor...

[Gray Ghost]

I have some vintage Weiand finned valve covers. They are going on Old Blue next week. The holes are both made for breathers. I am wondering if there's much difference in running two breathers versus one + PCV setup.

[Longhorn Man]

Picture you are in a kitchen right after the wife burns some food REAL bad.
To your left is a window, and to the right is a window.
Open up both windows.
Some smoke goes out... but not at a very good rate.
That represents 2 breathers.
Now, put a window fan in one, set on high. Put it in backwards so it'll blow the smoke out.
Lotsa smoke goes out, quickly, and the other window lets fresh non smoky air in.
This is the PCV system.

It makes a pretty big difference.

[72 cheyenne pdx]

Great analogy Longhorn Man. That paints the perfect picture.

[68K20 x Drill]

The PCV valve debuted on car engines in 1958, and was standard by 1960 without any legislation requiring it. Wonder if its better?

[Longhorn Man]

Originally Posted by 68K20 x Drill

The PCV valve debuted on car engines in 1958, and was standard by 1960 without any legislation requiring it. Wonder if its better?

well, it became mandated by federal smog regulations by 64... but none the less... a very good point.

[yenko427]

Not to steal your thread but if you only have one port on the back of your carb where can I hook it too. I have a holly 750 double pumper the one big port that I have is hook to the brake booster.

[Longhorn Man]

you can put a port on the intake too

[Gray Ghost]

Yeah I figured as much but I had to ask. I've never had a motor without one [for very long anyway]. Next question is where to get the fitting to adapt the PCV valve stuff to my breather opening [the one with the two slots like the old oil caps had].

[71Chevy4-speed]

Originally Posted by 68K20 x Drill

The PCV valve debuted on car engines in 1958, and was standard by 1960 without any legislation requiring it. Wonder if its better?

Helps oil stay cleaner, ever take a motor apart that didn't have one that had been in a daily driver for awhile. All the gases and small particulates have to go somewhere, I'd rather burn them then let it sludge up.

One thing I can tell you, don't plan on runnin Penz with no breather and not changing the oil very often, seen a pontiac 400 that snapped the crank in 2 places because of that, took 3 guys with chisels 4 hours to chisel the hardend gunk and carbon build up outta the lifter valley alone.

Hence part of the reason engines didn't used to last as long as they do now. ****ty oils and bad machining.

[Gray Ghost]

This one didn't have one for a long time, but it's not very gummy in there...mainly cause it all leaked out past the rings through the dual breathers.

I wouldn't use Pennzoil for anything....talk about sludge generation....

[67_C-30]

I disagree with theories of it being better. The PCV system is more for emmisions than actual evacuation of crankcase pressure. The rear vent on older SBC's or 2 valve cover vents are very effective, but do have the drawbacks of having an oily residue coming from them. A PCV won't even evacuate enough to be effective on a true high peformance engine, especially sustained high rpm engines like a circle track engine.

NOW - with that being said, none of this matters on a street driven or even street/strip vehicle. For a daily driven or street engine there's absolutely nothing wrong with the PCV, and it is the system I use for all of the street engines I build. It is highly effective for those types of engines and has been the norm for all engines built in the last 40 years.