Thread: Are Blow By Gasses Metered Air?

Only if you also open the PCV valve to filter instead of intake manifold!

Care to explain? Currently, I have nothing on one pipe of the "T" on the valvecover. It's open until I can get a filter, or cap it off. The PCV valve is still hooked up to the manifold, from the valvecover.

The valvecover shows slight vacuum to the "T" fitting at idle. So this is partially a vacuum leak? I know it's not supposed to see boost, so it has to be before the turbo.

Tekkie, thats weird, my T connection constantly blows air, never sucks.

With your VC open, you are letting unmetered air into the Intake Mani through PCV as Danja stated.

This thread was a quick Branch of this thread.

So if you want please continue the conversation there

Yea, I believe it is a vacuum leak sometimes. When the crankcase pressure is greater than that of the intake manifold, but less than or equal to atmospheric pressure, you will have a vacuum leak because air will flow into the manifold unmetered and unrestricted except by the valve size. Any other time, it is fine I guess haha.

But by venting both you make more room for fresh air in the manifold as well. I don't think you should cap the end of the T fitting, because I was under the impression that it was a good thing to have fresh air flowing in? At least, why else would they have designed the system the way they did? Maybe to dilute the blow by gasses with some fresher air before they entered the manifold?

In any case, I would leave the T fitting vented, and not capped. But if the PCV was vented, I suppose you could get away with capping it? It's all speculation haha.

Sorry to bring this back from the dead, but I'm redoing my IC piping and thought this important.

I'm currently running blow-through on an Avenir DET, my PCV hoses are all cracked and OE replacement is ridiculous so I'm thinking of making a catch can for the system.

Currently the PCV system is stock except for the T, which is disconnected since it has to be post MAF and I don't want to pressurize the crankcase. But this is bad because it is a slight unmetered air leak.

Since we've determined blow-by gasses are unmetered, can I get a 2 inlet catch can and connect it to the pcv valve and the VC "T" then do whatever with the other side (either an exhaust dump or turbo inlet)? And of course cap off the intake manifold ports.

That way the VC is always under vacuum which I hear helps with sealing of guides/seals/rings and even turbo seals.

Thoughts?