Does a car need a PVC valve?

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J-MacsMopars

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I am curious, does the car need the PVC valve on the valve covers? What is its function?
 
I say yes, it's there to evacuate crankcase pressure so you don't have leaky gaskets and blown seals etc.

PCV on one side, breather on the other.
 
Agree also it doesn't really hurt performance, at WOT if your carb is the right size the manifold vacuum should be under 1.5" so it will be pulling little or no crank case blowby into the intake.
 
thank you, does it need to actually be the valve, I have holley valve covers and they put a fitting in the back of one, but its not a pvc
 
I didn't use my pcv valve on my last 440 and it pissed oil out of everywhere, even the distributor was leaking. The engine was bad, but not having the pcv valve not hooked up sure didn't help. I use it now!
 
I think we need to "go back" a few years. Before there was PCV, there was "road draft." This was just what the name implied. This was a tube from some part of the crank case which went down under the car, and as the car moved, created a "draft" so as to help ventilate the crankcase. There was an intake breather up on the top front, generally.

When PCV came along, the road draft was replaced by the PCV into the intake vacuum

I believe, other than "smog" you could get by without PCV, but you really should have some form of "draft." I actually ran open hoses on both VC of my car this summer.........just open hoses down to the underside of the car. "Draft" if you will

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thanks for the info. Now I need to add a pvc valve to the valve covers.
 
I'm probably in the minority on this subject, but I don't use a PCV valve. I use 2 breathers (one on each valve cover) and have never had an issue with leaks. I used this setup on 4 different engines over the past 21 years on my Barracuda, no problems.
 
The PCV valve is designed to prevent oil vapor being spewed into the air while eliminating crankcase pressure. As previously stated, it will prevent oil from being forced through the various engine seals.

- But it is also supposed to increase power. Prior to the creation of the PCV valves, the crankcase pressure was relieved by means of a 'dump tube' directed down the back of the motor. It simply allowed internal vapors to blow out of the engine and into the air unfiltered. Using a PCV setup is actually a better way to pull that pressure out.

Using breathers alone can often be sufficient to release internal pressure. - But often it will mean using more breathers to accomplish as much.


For some of our drag motors we would install crankcase evacuation systems which are designed somewhat similarly. But instead of having the engine's vacuum pulling out the internal crankcase pressure you run a hose assembly down to your exhaust and the exhaust pulls the pressure out with even more suction. The crankcase evacuation systems were supposed to actually create a negative pressure inside the crankcase and make even more power yet. Not exactly as environmentally friendly though.
 
i have found that a PCV valve that is not right can cause to much water to be in the crankcase. so change it once in while. all the acids in your oil are water based. and for every gal of gas you burn almost a gal of water is made.
 
i have found that a PCV valve that is not right can cause to much water to be in the crankcase. so change it once in while. all the acids in your oil are water based. and for every gal of gas you burn almost a gal of water is made.

Back when I was in school, my instructor told us that the PCV valve was pretty simple. More or less a check ball system to prevent fluid oil from getting through but still allow vapors to pass. When they stop working it's usually because gummy oil residue has stuck the check ball. I was told that inspecting them was a simple matter of taking them off and shaking them. If the ball seemed to move freely back and forth without any sign of sticking, they were OK. All we ever had to do to fix them was to clean them in parts solvent.
 
"The main purpose of the PCV (positive crankcase ventilation) valve is to recirculate
blow-by gases back from the crankcase area through the engine to consume unburned
hydrocarbons. Blowby is a mixture of air, gasoline and combustion gases forced past the
rings on the combustion stroke. The PCV system usually has a tube leading from the
crankcase to the carburetor or intake manifold. Vacuum within the engine intake manifold
pulls blowby gases out of the crankcase into the combustion chamber along with the
regular intake of air and fuel.

A valve can become clogged with sludge and varnish deposits and trap blowby gases in
the crankcase. This degrades the oil, promoting additional formation of deposit material.
If left uncorrected, the result is plugged oil rings, oil consumption, rapid ring wear due to
sludge buildup, ruptured gaskets and seals due to crankcase pressurization, oil thrown out
around the filler cap and consequent rough engine operation." Amsoil TSB: MO-2004-04-03

This sums up what I've always understood. I've also always been told that a it's not as important on a quarter mile car as long as 2 breathers are employed because it doesn't run for extended lengths of time at temperature but that on a driver, if you don't have good flow venting through the crankcase, you run the risk of your engine developing more sludge sooner. The suction on the PCV promotes that constant venting and flow.
 
Last year I changed from an Edelbrock to a Holley and lost a vacuum port. I left the pcv disconnected and remember thinking I will let it breathe on it's own until I could get a breather filter. I was 15 miles down the road when the light bulb in my head went on and I remembered the pcv won't open without vacuum and I'm building pressure. I pulled into the closest parts store, opened the hood, and found my water pump covered in oil and little puddles of oil on top of it. My intake gasket blew out from the pressure. I bought a nice K&N breather which slowed the leak, which I soon fixed, but it never ran the same. I reconnected the pcv a couple weeks later and it ran like it always used to. Therefore, I recommend a pcv valve.
 
I run one with a moroso breather! Worked great on the dyno! I have seen vac pumps on certain engines on the dyno worth as much as 22hp! Crankcase ventilation is required on every engine.
 
see there my friends here have tons of great info. i remember when thy started using PCV valves. the only smog part my dad thought was good. cause the engine had a LOT less dirt going in the crankcase.
 
see there my friends here have tons of great info. i remember when thy started using PCV valves. the only smog part my dad thought was good. cause the engine had a LOT less dirt going in the crankcase.

That's what my instructor told us at tech college back in the 70s. A lot of the guys in the class were racers and the teacher was adamant that if we chose to get rid of the rest of the smog equipment to increase power we'd see gains. But if we got rid of the PCV setups we'd be shooting ourselves in the foot.
 
Another thing to be sure of is baffling in the valve covers at least as good as factory valve covers is mandatory IMO. Without that no matter what you do, PCV or not, is gonna be a mess.
 
The PCV (Positive Crankcase Ventilation) valve extends engine life. Moisture, and other byproducts of combustion need to be pulled out of the crankcase otherwise they turn the oil acidic and produce sludge. The old "road draft" tubes worked OK if you were moving at a pretty good clip, and didn't mind breathing leaded oily vapors from the cars around you.

The PCV valve wasn't a strictly a product of the "smog era" either. Jeep has used them since the beginning in WWII.
 
Another thing to be sure of is baffling in the valve covers at least as good as factory valve covers is mandatory IMO. Without that no matter what you do, PCV or not, is gonna be a mess.

More info please.
 
I was taught that the check ball in a PCV valve was to prevent flame from reaching the combustible vapors in the crankcase in case of a back fire. Gases can flow out to the base of the carb, but if the carb spits back, the valve closes and no flame can reach the valve cover.
 
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