I have read too many PCV system threads to count and have found a lot of good answers spread out over them. Unfortunately, I have also seen people who post incorrect things, often based on their often uninformed opinion.
So that being said, I will attempt to consolidate my understanding, with a lot of information that I have gathered through research, as well as inputs from venders of this forum.
First let me explain the SRT-4’s stock PCV (Positive Crankcase Ventilation) system. The simple answer has two parts.
1- To vent the combustion gasses the leak past the piston rings and vent oil vapors that build up in the crankcase and replace these gasses/vapors with filtered fresh air.
2- To improve emissions by re-routing these gasses/vapors back into the combustion chambers via the intake manifold to be burned and sent out your exhaust system.
This is a basic picture of the PCV valve itself in the closed position. This should be how it is during boost, backfire or with the car off. In all these conditions no crankcase or blow by gasses should be vented through the PVC valve back to the intake.
In this picture the PCV valve is in the open position. This is the state of the PCV valve during moderate intake manifold vacuum (or normal throttle) providing maximum flow of engine vapors back to you intake.
This last picture shows the PCV valve during high intake manifold vacuum (or during engine de-acceleration, or idle) during this state the PCV is still open, but does not flow as much.
This first picture shows our basic stock PCV set-up operation during idle or cruise. During this time your boost gauge should read apx -20vac for idle or roughly that for cruise (depending on if you are accelerating or de-accelerating). Notice the air flow. Because of the vacuum present at the intake the PCV valve is open and passing the gasses/vapors present in the valve cover. Clean air is also pushed/drawn into the valve cover through the breather side.
This picture shows the basic stock PCV operation during boost. Again take a look at the air flow. The vacuum at the intake is now boost. This pressure is going to travel up the line and push the PCV closed. With nowhere else to vent the gasses in the valve cover will be routed through the breather nipple back into your air intake.
With all that being said the stock set-up has its inherent faults. First, all that crankcase oil and blow by vapor goes to one of two places:
1. It gets routed back to your intake manifold. There some of it gets burned and expelled through your exhaust. The rest of it drains down into you throttle body/upper pressure pipe/intercooler. Anyone who has swapped their pipes or intercooler can back this statement.
2. It gets routed back to you air intake. Here it can gunk up you turbo/lower pressure pipe/intercooler.
3. The stock PCV valve has been identified as a probable boost leak. See one example of many:
69cuda340s
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Join Date: Nov 2005
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My PCV leaks boost. I make a boost leak tool as shown by others on these forums, connected my air compressor hose, and adjusted air pressure up until the boost guage inside the car read 16 PSI of boost. I found two leaks on the hot side by listening with a 3/8" piece of fuel line hose (it amplifies the noise, works great). OK, but back to the PCV, after all clamped areas were leak free I kept hearing air from inside the engine. I was draining the oil at the time and could feel air coming out of the oil drain plug and was like WTF? So I took a wrench and loosened the PCV and pulled it out of the valve cover (turn it counter clock wise by the nut with a wrench, it twist right out). With PCV valve out air was no longer coming out of oil drain hole and I could feel the air coming out of the PCV valve, which is still connected to the throttle body hose. Not a lot of air, but it was coming out of there for sure. Now my car only has 1,000 miles on it and the PCV is not gumbed up or sticky. So I ask my son to get in the car and look at the boost guage. Then I put my finger on PCV valve and boost goes from 16 to 17 PSI then I let my finger off and it goes back to 16 so boost is leaking there. Haven't checked my air filter yet but there may be some oil in there. Anyway, after this test I do think a check valve in between the intake and newly installed catch can would stop this leak. I may try and get a PCV from the auto parts store that does not leak and just go that route because there is no reason the PCV should be leaking boost like mine is being the PCV valve is a check valve.
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There are a few modifications you can perform to help with these problems.
The first is the oil catch can (CC). There are at least two tried and tested set-up for this application. A CC can be purchased by various venders.
1. Using a CC in line between the PCV valve and the intake manifold to collect oil. Also use a breather style filter on the breather side of the valve cover.
2. Using a CC on both the PCV line and between the valve cover breather and the air intake.
The second is installing a check valve (CV) in line with the PCV valve and the intake manifold (as close to the manifold as possible). As many know the PCV valve is actually a check valve itself. However, as many have noted, the stock PCV valve frequently leaks boost past it into the valve cover. This is not a desirable boost leak for a couple reasons. I will not get into it but you can find it later in some of the good links that I will provide. To remedy this install a better quality CV. Take a look at this pick depicting a CV installed with a CC. I believe this is the best set-up for our PCV system.
I personally recommend the CV that PTPerformance sells. There has been a lot of shit about the effectiveness or safety concerns of their or any check valve. Let me clear this issue. You absolutely want your PCV to work during vacuum but not leak during boost. PERIOD. Our stock PCV (check valve) opens at -.4vac. The PTPerformance CV opens at -.2vac. This shows that it will not stop the stock PCV from opening under vacuum. The PTPerformance CV is also rated to hold 125 PSI. Boost leak stopped. It is also rated for 220degree f. and a flow rating higher than would ever be needed. I am plugging PTPerformance because their CV works. Yes, you may be able to go to a hardware store and by one but you don’t know the ratings and it may be a piece of shit. Like these: The first with unknown readings and the second that warped under the heat.
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These are some other good targets for more/other info. Some that helped me put this post together:
http://cjsupra.kendra.com/PCV-Can.html
http://s6.invisionfree.com/Michigan_...showtopic=1089
http://www.boostcontroller.com/qandaiframe.php
I hope this post helps out some of you. Others will STILL remain skeptical or have their opinions. That’s cool too. I just urge you to make INFORMED decisions, not just spit what they have heard.
Adam
