Is the PCV valve and related components REALLY necessary?

[GuysMonteSS]

Just want to relate my experience of not running a PCV on my BBC.
It was just something I wanted to try,so I removed the PCV and plugged the port it goes into at the carb.
I had a breather in both valve covers.
So off I go for a test drive and lordy did it ever start to smoke.
Popped the hood and had a look and believe it or not but oil was coming from,of all places,the gasket where the distributor mates to the intake.So oil was running down the engine and onto the headers,what a stinking mess.
Put the PCV back on and it was back to normal,no oil being forced out of places where it shouldn't come out LOL
I believe that if I were to take my big block further that a vacuum pump as 565bbchevy described above would be on my "Want List".
Guy

 

[HAFROD]

I have always ran a PCV on one side and a push in (sealed) cap on the other. If you are running aftermarket valve covers be sure there is a baffle in the one the PCV will be in. Without a baffle, it will suck oil. The reason I run a push in cap on the other side is to keep the engine sealed and drip/leak free. The PCV will vent both sides. With an open filter on the other side, I don't know if the PCV could pull as much

 

[Bonnewagon]

The condition is called BLOWBY, and it is the result of combustion gasses that get past the piston rings and into the crankcase. As mentioned, ancient cars had a road draft tube that pointed aft and used the suction affect of airflow under the car to vent the gasses from the crankcase. When the car stopped, so did the suction. The PCV valve merely directs the gasses into the manifold so they get burned up. A two stage system also vents a valve cover into the air cleaner since there are conditions when there is little manifold vacuum so the system works at all times. Disabling the system results in oil being expelled from wherever is handy, like the dipstick tube. As for the charcoal canister, it is there to store gasoline fumes from the gas tank and float bowl when the motor is off, then when it starts, sends them to the intake to be burned. Neither system affects performance in any way.

 

[Silent viewer]

I have done allot of research on this for my boat engine and I have figured out that allot of people (including me on the boat engine at the moment) run a breather on each side and it seems to work fine. the way it was explained to me is the engine is going to push the fumes out of the vents on its own and I can literally see little puffs of vapor on occasion coming out of the motor. the difference here though is you run 3000-5000 rpm at all times so the PCV I guess never opens during that time. on a car engine I would scrap everything off the canister and run only a PCV valve to one valve cover and a breather on the opposite side. that will cause air to come in one side and pull through the entire engine and go out through the PCV into the carb.

 

[ssn696]

The PCV is cheap and only puts one hose across the engine to the carb. Works fine until your spend lots of time over 4000 RPM, blowing combustion gases past the rings. At that point, you need a header or pump evacuation kit. I've seen a dipstick launch right out of the tube when a friend forgot and put old school finned breatherless rocker covers on and revved the motor. The 265-283-327 motors had an intake manifold that had a push-in breather/oil fill next to the thermostat housing.

 

[565bbchevy]

I know a guy that replaced the valve covers on his BBC boat engine with some pretty anodized valve covers but he did not use any of the original breather system because he did not like how it looked, first time out it forced all the oil out of the engine and it locked up and he had to be towed back. Obviously boat engines with sustained RPM's need better evacuation than a typical car but this shows how pressure can build up in the crankcase.

 

[pontiacgp]

The PCV is cheap and only puts one hose across the engine to the carb. Works fine until your spend lots of time over 4000 RPM, blowing combustion gases past the rings. At that point, you need a header or pump evacuation kit. I've seen a dipstick launch right out of the tube when a friend forgot and put old school finned breatherless rocker covers on and revved the motor. The 265-283-327 motors had an intake manifold that had a push-in breather/oil fill next to the thermostat housing.

the other cover has a breather that goes to the air cleaner. I think that breather vents the pressure when the pcv is closed. On all out circle track engines they always has two breathers on the diver's side valve cover but none the other side. There must be a reason for that but no one could ever explain it to me.

 

[565bbchevy]

I have seen the valve covers for circle track with the two breathers on one valve cover only but did not know everyone put those on a specific side.

 

[CWPottenger]

After reading this thread I got to thinking... Maybe a PCV valve would help solve some of my oil leak issues when I go over 5K rpm. So I installed one in the driver side valve cover and plumbed it to the vacuum port on the bottom of my TBI. I had breathers in before so I left the breather in the passenger side valve cover. Went for some aggressive back road pulls. I have less oil issues for sure. I might still have a small leak at a gasket on passenger side, but driver side was oil free this time and passenger wasn't smoking, but still had some drips on cement( maybe just residual). This also solved my huge issue of violent backfires on aggressive deceleration. Since I added the PCV my engine now just has that mean lean decel rumble through the exhaust. Never had issues like that before with just breathers, but then again never had an engine like this before either... 🙂

 

[ssn696]

I think the circle track guys always turn left, so it seems like any oil above the right cylinder head that pools and can't drain back is at risk to puke out the vents and burst into flame on the red-hot exhaust manifold.

The breather in the air cleaner offers a path for filtered fresh air into the crankcase so the PCV is not pulling a suction on the crankcase. Any exhaust gasses get pulled along for the ride out of the engine.