Necessity of PCV Valve?

[04EP3Hatch]

Well as most of you have seen I've gotten rid of my supercharger setup to go turblow, and I have most of the necessary components so far but I want to run a catch can setup, I completely plugged the ports for the Pcv valve and idle air assist valve with npt plugs, and I am looking to run a 2 line catch can setup, one from the valve cover and one from the Pcv valve, but I'm wondering is it necessary to have the valve installed? I ask this because I wanted to get an adapter so I can unscrew the Pcv valve and use an AN. Fitting with straight line running to the catch can. Anyone done this or heard of it being done?

[Drew1d]

Isn't the PCV a one way valve that lets out pressure from the crankcase and prevents moisture getting in? So it's one wayness is important.

[04EP3Hatch]

Well moisture is going to get in no matter what, the breather at the valve cover has no one way, and B series guys use large adapters that bypass the black box just so they can run a line from the adapter to a catch can

[andyman97]

Isn't the PCV a one way valve that lets out pressure from the crankcase and prevents moisture getting in? So it's one wayness is important.

This is exactly correct. Don't eliminate the valve, there's no good reason to.

[andyman97]

Here is a snip from a post I wrote up about the pcv:

The pcv valve is a positive crankcase ventilation valve. Positive = pressure. Pressure and vacuum are opposites, pressure causes force and vacuum creates a suction.
The pcv is a one way valve, it only allows particles to leave the crankcase, not to go back in.

What I see lots of people do is drill out the valve altogether. This can let foreign matter into the crankcase and can have a negative effect on engine idle and oil pressure.

So why does the pcv have a vacuum line from the intake manifold? Emmissions. It's so you don't blow oil vapors to atmosphere. Why does the valve cover breather go back to the intake? Same reason, emissions. It's so that vapors go back into the combustion chamber rather than vent to atmosphere.

What about the breather vent in the valve cover? It's a failsafe or backup, in case your pcv clogs or can't properly vent pressure buildup in the crankcase.

Wait a second, I thought the engine was always in vacuum, what purpose does this system have if the engine isn't boosted? Well, your map reading is in the intake manifold. While the intake manifold is seeing vacuum, the combustion creates pressure that slips past the rings and gets into the crankcase. Your manifold pressure or vacuum is not going to be the same as what is in the crankcase.

Ok, so how does a turbo affect the system? Well, boost pressure results in a production of a more powerful combustion and a lot more slips past the rings. If you left the system in tact like stock, you'd have major problems because the intake manifold is seeing pressure and the PCV is trying to vent pressure into the same vacuum line off the manifold. There's nowhere for the pressure to go. So it's a good idea to vent the PCV and breather to atmosphere or a catch can. This is the reason many people remove the valve completely, but I would recommend against it for the reasons above. The valve can effectively vent the pressure and if it clogs, replace it.

If I think of anything else pertinent, I will add to this post. But this is the jist of how it works and how to PROPERLY set it up if you're boosting.

[BeaterEP]

Great post! Think that should clear it up for most folks man! :thumbu:

[Drew1d]

I'm sorry, just to clarify for my own knowledge. Onewayness ok, but not really for moisture, right?

[andyman97]

The reason to keep it is all in my post above, adverse affect on idle and oil pressure.

[BlownSi05]

I had heard of B series guys doing this as well, but it does not make any sense. Why would you block off a valve that vents gases and oil vapor to regulate crank case pressure? Keep the PCV, install a catch can, done.

As far as moisture goes, it should be eliminated by the heater element at the valve cover breather. It is a little metal loop that heats the air that travels through that little hose between the intake and valve cover. Heating the air removes moisture. When I first installed my catch can I had not put this piece back into the mix and just left it hanging under my intake. I noticed that the oil that was condensing in the can was turning color and texture, just like when water is added. After freaking out trying to figure out how water was getting into the motor (and some help from some super awesome people here), I cut the hose from the valve cover and put the heater element back the way it was; no more moisture in the oil/motor. You can even put the little breather filter like many of the B series guys do, but you have to have that little heater coil somewhere in the mix.