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It serves no purpose if your car has a working PCV system. There are only 3 cars on this Forum that don't have 'traditional' PCV operation (bypassed through a trap), and they still don't need that breather. It's a cosmetic thing only. Reminiscent of the old muscle car days, nothing more.

It's actually better if you, instead of running it through a breather, run a catch-can setup. Then you're not venting oil to the environment, you're able to re-use it or safely recycle it. Don't need to make a bigger mess than you have to...

razmatazz wrote:Is that what i think looks like some form of an air filter were your oil cap i suppose to be? if not what is it

A vacuum leak.

That would only be a vacuum leak (and not in proper terminology) if someone forgot an o-ring on an L36 PCV valve. Most cars will see a positive HIGH pressure under the valve covers.

unmetered air post maf = vacuum leak, beather is ONLY need when you block pcv function or turbo(reason for high pressure under valve covers). It's a poor way of doing it. Catch can is the better way.

The cylinders can't suck air in through the breather, unless the PCV is stuck. A properly operating PCV will not be affected, except that you're losing oil out the breather, and if you bypass the PCV, it needs a place to vent the fumes.

Larz, I think you're missing something in the operation here. All cylinders, regardless of compression, have some amount of blow-by. This puts a slight positive pressure in the crankcase, which also migrates to the cylinder heads. This is the purpose of the PCV system:

Positive Crankcase Ventilation

The PCV system takes that POSITIVE pressure with the hydrocarbon-laden (from fuel) blow-by, and what oil vapor in the crank case and cylinder heads it mixes with, and recirculates it back to the intake where it's re-introduced into the combustion cycle to be burned rather than pollute the environment. This does have a slight negative effect on effective octane, which is why one of my cars is running a catch can system.

So what we're talking about here, is a car with NORMAL function....if you were to remove the oil fill cap and put your palm over it, you would feel a very slight POSITIVE pressure. Not vacuum.

Your description makes it sound like 'vacuum leak' which sounds to most people like it would affect the amount of MANIFOLD vacuum, and this is simply not possible. The two systems are completely isolated from each other, and using the term 'vacuum leak' is deceiving at best.

willwren wrote: This does have a slight negative effect on effective octane, which is why one of my cars is running a catch can system.

Me too!

willwren wrote:Larz, I think you're missing something in the operation here. All cylinders, regardless of compression, have some amount of blow-by. This puts a slight positive pressure in the crankcase, which also migrates to the cylinder heads. This is the purpose of the PCV system:

Positive Crankcase Ventilation

You said it right here, Positive pressure....not equilibrium by using a some fancy filter.

The PCV system takes that POSITIVE pressure with the hydrocarbon-laden (from fuel) blow-by, and what oil vapor in the crank case and cylinder heads it mixes with, and recirculates it back to the intake where it's re-introduced into the combustion cycle to be burned rather than pollute the environment. This does have a slight negative effect on effective octane, which is why one of my cars is running a catch can system.

YES. Your loosing the concept, the crankcase gases are introduced "back into the intake" on factory setups. If you put a filter on the front valve cover the crankcase is pulling/losing unmetered air threw it like the OP's ( thats why there are o-rings on valve cover caps, pcv valve, even your oil dipstick...serves for more than one purpose.) If its run like the factory system it will suck fresh metered air from the front of the engine to the rear, back into the intake (closed system). This can not be accomplish using a breather (open system).

Your description makes it sound like 'vacuum leak' which sounds to most people like it would affect the amount of MANIFOLD vacuum, and this is simply not possible. The two systems are completely isolated from each other, and using the term 'vacuum leak' is deceiving at best.

How is it isolated if you just said its re-introduced back into the intake?

So what we're talking about here, is a car with NORMAL function....if you were to remove the oil fill cap and put your palm over it, you would feel a very slight POSITIVE pressure. Not vacuum.

Not arguing this, im saying with normal function its metered, using a vc breather it is not.

Here is my junk setup. Guess i'm missing something and decided to drill holes in my supercharger and valve covers for fun (closed system using factory pcv function just externally routed; enjoy

Larz, the PCV valve itself is a check valve. You don't introduce a vacuum leak with a breather, and if you'd try it yourself, you'd see on your boost gauge that it doesn't happen.

To do the bypass or catch can, you don't need to drill any holes. Just machine a sleeve to replace your PCV and add a fitting to the PCV cover.

http://i21.photobucket.com/albums/b251/ ... C07987.jpg

http://i21.photobucket.com/albums/b251/ ... C07988.jpg


Back on topic, there are dozens (if not hundreds) of cars here that have run a valve cover breather for cosmetic reasons, and none that I recall ever induced a vacuum leak. It's so far from the source, and at such a low level, its effect on the system is technically zero.

We have a GenV setup similar to that on the Forum.

And when the PCV system fails, it fails in the OPEN (breathing/venting) position. And it's rare. Most of us replace our PCV's more often because they're so inexpensive. I can't recall any car I've ever owned having a PCV problem in the last 25 years.

Unless I missed your point?