I've been resurrecting my 1972 for many years and now I'm reinstalling my PVC valve. There are many varieties, are they interchangeable?
Would a PCV valve from a 350 work in a 454?
What would happen if a different one is used?

 

PCV valve flow depends on the specific engine make up

For example when the piston rings are worn and blowby has increased, a larger pcv valve orifice is needed to flow more crankcase byproduct volume

A PCV valve is not one-size-fits-all and needs to be modified or adjusted (sometimes by running two pcv valves in parallel for example)

The correct way to determine how much pcv flow (crankcase flow) is needed at idle, cruise and wide open throttle, is to measure the crankcase pressure
Crankcase pressure needs to be set to approx 0.8" to 2.5"Hg at all times to maintain a vacuum in the crankcase at all times
Anytime crankcase pressure rises above roughly 0.25"Hg to +0.01psi (above atmospheric) crankcase gas will contain large oil droplets and push oil through seals causing oil leaking, engine smoking, oil pushed into the intake manifold, oil spray, etc...

This is target Crankcase pressure as shown on a pressure gauge


you can use a 1-bar map sensor to get an idea of the crankcase pressure
for example
https://forums.holley.com/forum/holl...nhg#post417512

Or use a pressure gauge of appropriate resolution


wide open throttle crankcase pressure is measured after the air filter where the air filter tube attaches to the crankcase on all OEM engines and this should be set and maintained more precisely as the engine becomes more performance oriented.

 

Thanks King for the in depth response to my question.
I guess the bottom line for me is to use the stock PCV valve for my unmodified 454 as GM intended.

However I see many engines with breathers in each valve cover and no PCV valve.
Is the PCV valve necessary?

 

Yes, if you don't want to coat your engine with a thin film of engine oil mist.

 

Sunflower: That's what I heard. I've been running with two breathers for a while but no oil mist film, I guess eventually I would see it.
No matter, I just finished reinstalling the PCV valve.
Thanks for your input.

 

That's unusual. Ok.

 

Hello,
I believe the PCV was part of the attempt to control emissions whilst the valve cover mounted breathers were just that...crankcase breathers.
Regards...

 

PCV is an oil cleaning and piston ring draining cleaning mechanism
PCV is a oil leak prevention mechanism
PCV enables high mileage by preventing deposits in the oil system and keeps oil out of engine seals which prevents leaking
Blow-by is mostly water, for every gallon of fuel burnt will produce around 1 gallon of water
PCV keeps water out of engine oil
Blow-by contains mostly water and CO2. CO2 interact with water to form carbonic acid which attacks everything inside the engine and the oil. CO2 and water component of exhaust gas is one reason why exhausts rust easily when the engine is shut off water condenses from exhaust in the presence of CO2 causing rapid oxidation.
PCV keeps CO2 and water out of engine oil which protects the oil and engine quality.

PCV is the most important system on any combustion engine and the least understood

If anyone would like more detailed explanations i will be happy to go over each concept individually

 

Hi Alan 71.
I agree about controlling emissions.
I always thought the PCV valve was an emissions control device.
The idea in sucking valve cover fumes back into the engine does not sound good.
But I'm no expert, that's why I ask questions.
But what I do know is I've been a Forum member for 21 years and during that time I've seen engines with solid valve covers on each side, or with a solid cover on one side and a breather in the other, or a breather on both sides, or a PCV valve on one side and a breather on the other, and finally (my new stock set up after running 2 breathers) a PCV valve on one side and a hook up to the air cleaner on the other.

 

King, you just gave the best reasoning ever to keep the PCV valve.
That's excellent information/explanation.
Now I'm glad I returned to the stock set up.
Many thanks.