I'm getting ready to purchace a pair of billet breathers...any advantage/disadvantage to running a PCV valve?

Well, ....PCV Positive Crankcase Ventilation. Do a search as there are plenty of threads on this one. Short answer is yes, run one.

HA! Been spending too much time doing home improvements! I corrected it to PCV...LOL

It's the Law, you won't pass a visual smog/safety check!!

Pre-'64 cars are exempt.

pdq67

if you dont run one you will most likley push out oil pan and valve cover gaskets

Billet breather & matching billet PCV valve just ordered. Thanks guys! :thumbsup:

if you dont run one you will most likley push out oil pan and valve cover gaskets
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Really? :noway:
Explain why this would be so

PCV systems make the engine oil stay cleaner for longer and help remove moisture from inside the engine as it boils off. No reason not to run one.

Run one for sure.

A proper PCV system will do two things for you; reduce oil consumption and more importantly, eliminate the possibility of a crankcase explosion. Run one.

Tom

I've never opened a PCV valve, but it seems to be nothing more than a check valve of sorts. How does this help the engine more than a breather?? I'm very curious as I've never really had it explained to me.

PCV systems make the engine oil stay cleaner for longer and help remove moisture from inside the engine as it boils off. No reason not to run one.
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This I agree with 100%



A proper PCV system will do two things for you; reduce oil consumption and more importantly, eliminate the possibility of a crankcase explosion. Run one.

Tom

Contamination during light load, idle etc,,, yes, consumption you will have to explain ;)

A PCV is a one way valve, built that way in case of engine backfire
You do not want the pressure of a backfire entering the crankcase
It only works at light load, idle any time there is a vacuum in the intake manifold
It does help relieve some of the contaminates that are boiled off after the oil gets to a reasonable temperature so I suppose you could say "cleans the oil"
This is not really true though, the heating of the oil is what removes the water & acids that can be boiled out & turned into vapor, steam what ever.
The vacuum is what helps to remove the vapors for most of the time the engine is in operation

What it does not do is lower crankcase pressure under heavy loads
You do not have a vacuum under heavy loads
This is what the breathers are there for

Wolfplace, thanks for the explanation. That makes perfect sense. I've never run a PCV valve, and didn't understand why I should.Thanks again.

Reminds me of a recent expierence I had. I know a guy with a 66 283 in his 65 Malibu. He has the old stock Chevrolet script valve covers and has no breathers or provisions on them for a PCV connection or oil cap, he is using an early 60s setup with oil fill on the intake. The back of the block appear to be drilled for a PCV. Its a 66 block and the valve covers appear to be early 60's. He insists on using the stock valve covers unmodified and I dont see how where he will be able to run a PCV system. The earlier blocks appear to use a provision on the back of the block for this, but his block is closed off or casted over from the factory. I am not sure what to tell him on what to do about a PCV system on this anomaly.

The oil fill tube either has a fitting to connect a 3/8" hose and PCV to the carb, or the fill tube is vented through the filtered cap - either way, it lets the crankcase pressure equalize at all speeds.

Contamination during light load, idle etc,,, yes, consumption you will have to explain ;)



Most PCV systems have a steel wool type screen in them to collect oil vapor and allow it to run back into the crancase before it gets sucked into the carb. Some even have an oil collector like you would see on a shop air compressor to do the same thing.

Tom

Most PCV systems have a steel wool type screen in them to collect oil vapor and allow it to run back into the crancase before it gets sucked into the carb. Some even have an oil collector like you would see on a shop air compressor to do the same thing.

Tom

How does this help with oil consumption?
What if you had no PCV & just a breather?
So my question is still how does a PCV valve reduce oil consumption?

BTW, most do not have a screen like you describe they have an oil separator or baffle in the valve cover so you don't pull raw oil into the intake just the vapors
At least that is the plan,, :D

Think of it this way, there is as much air movement in the crankcase from piston movement as there is in the cylinder and intake. And a constant oil mist.

The pcv provides a path to move at least some fresh air through the crank case, and a positive means to vent it, ie, the intake manifold.

If the crankcase is not vented, it will build up pressure and come out somewhere, as it heats up, gets thrashed around.

The vacuum pumps/extractors are the best development of this, wherein it is attempted to lower crankcase pressure to reduce the pumping losses in the motor.

Think of it this way, there is as much air movement in the crankcase from piston movement as there is in the cylinder and intake.

Crankcase volume is constant - as one piston moves down another moves up the same amount.
The only gas volume added to the crankcase is from blowby.

The crank case volume is constant, but the piston movement is going to push that air all around exactly like the topside does in the intake track. It is called pumping loss, and takes energy from the crank.

In 2 strokes, it is the intake track and the pressure is also used to operate the fuel and oil pumps.

So there is pressure and movement there. Plus oil mist. And heat. And the blowby from the rings, however slight it may be. Note that a leak down test of less than 10% is considered good.

So the crank case needs to be vented. PCV is just a controlled way of providing sufficient venting so that nothing from the crankcase gets out into the air... The positive part means the air vent rate is (well originally was supposed to be) high enough so that there is atmospheric or slightly less pressure in the crankcase. Ie, more air gets sucked into the intake than wants to leave due to the heat and thrashing.

If you seal it up, it will push oily vapor out somewhere....

In the old days it was a road draft tube. Now its pcv. The ultimate level is the evac systems used to get the last bit of ring seal and to reduce pumping losses....in lots of drag motors.

A PCV (Positive Crankcase Ventilation) valve takes compression blow-by out of the engine more than anything else. It is called "positive" because it works under vacuum from the intake manifold/carb.

Valve cover breathers are a form of ventilation, but not positive ventilation. Some of the old small block Chevy engines had a vent pipe that came off the back of the block near the distributor mount which served as ventilation, along with the push-on oil filler cap.
Every engine has some amount of combustion blow-by, even those with "zero-gap" rings. No such thing as a perfect seal in a cylinder.

One possible consequence of not having a PCV or other means of ventilation is that your oil dipstick can get launched. This is cause by the wind generated by the crank rotation, combined with blow-by, particulary at higher engine RPMs. I know of one guy who was launching his dipstick and swore someone was getting under his hood and doing it just to annoy him, until he discovered the problem.