metako42

Got a question about the oil breather hoses on a S13 redtop SR20DET.

When the engine is idling or off boost and there is vacuum in the intake manifold then the PCV opens and oily air is sucked out of the cam cover and into the intake mani.

Now does this mean that because the air is being sucked out of the cam cover on the PCV side, that air is being sucked IN on the other side of the cam cover through the T pipe front hose, which is connected to the intake pipe between the AFM and the turbo? So that fresh air is sucked in the turbo side and sucked out on the intake mani side?

I understand that when there is boost in the IM then the PCV should shut off and there would be no vacuum and then the turbo intake pipe would start sucking air from the T pipe.

Mikester

Under vacuum, the intake mani is sucking air from the crankcase to the tee fitting, then through the rocker cover and out the PCV valve into the intake mani. Under boost, the turbine sucks air/oil vapor out of the crankcase/rocker cover, & blows it through the charge piping to the intake. In otherwords, the way the OEM S13 red/blacktop systems are set up; the intercooler is basically a catch can... which is why you will always find oil residue in stock SR charge piping.

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metako42

Does this mean the T fitting on the turbo side sees vacuum?

also under boost the air the turbo sucks on from the T is a mixture of scrubbed air from the rear hose of the T (from the factory separator can and the crankcase), and oily air coming into the T from the cam cover? The factory mixes clean and oily air?

Mikester

Yes, correctly hooked up, the tee always sees vacuum (Positive Crankcase Ventilation ); either from intake mani vacuum or suction from the turbine.

Yes, the factory setup mixes clean/oily air. I apologize- I forgot about that separator on the OEM setup, which keeps much of it out. Be that as it may, there will still be residual oil vapors from the rocker cover that get sucked into the charge piping via the turbine on the OEM setup... Which is why aftermarket catch cans come in handy. Also, there is a thread here with a couple vastly improved options for catch cans for S13 SR's. I am at work and the internet here sucks or I would post it for ya... but it's definitely worth a read.

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metako42

XJust so I get this straight, so when there is vacuum then the T actually sucks IN air from the turbo inlet, but when there is boost then the air is sucked OUT of the T by the turbo inlet? So the direction of the air in the T changes depending on the presence of vacuum or boost?

Reason I am being so precise is that I was thinking of rerouting the hose from the front of the T into the hose going into the factory separator from the crankcase so that the air is scrubbed before going the air intake pipe. But if the T is actually sucking air IN when in vacuum then it will suck in air from the crankcase breather hose!

Mikester

Close...

Under vacuum, air is sucked out of the crankcase (below the stock separator tank), thru the rocker cover baffling, out the PCV valve & into the intake/combustion chambers. None of the air that has already been metered is being taken away from the turbine... and if it is; it's a very miniscule amount.

Under boost, the turbine draws air out of the crankcase & rocker cover, and routes it thru the charge piping to the intake/combustion chambers... again not losing any of the air that has already been metered; but taking on a slight bit of extra air in order to keep crankcase pressures down.

What you are talking about is doing a catch can. With many aftermarket exhaust manifolds, the stock separator tank has to be removed for fitment anyway... Here, read this thread- It explains things much better than I am lol: #/f/tech-talk/235851...can-setup.html

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Kingtal0n

The vacuum at that "T" is supplied by the intake manifold. Look at the opposite side of the valve cover. See the PCV valve at the back? thats a one-way check valve that connects to the intake manifold to supply that vacuum, that you just mentioned, to the T, that does draw air in to the valve cover FROM the compressor inlet.

and yes, during boost, the direction changes, now the "T" fitting FEEDS the compressor inlet airflow, not much but some. Its supposed to help with venting the crankcase, yes, because during boost, the other valve (connected to the intake manifold) is SHUT. or should be.

and turbine usually refers to the exhaust. he means compressor, not turbine.

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5.3/4l80e/turbo 240sx playthrough:
https://tinyurl.com/turbo240

metako42

Thanks for your answers Mikester, that is very helpful. And thanks for that link. I've read it all and now have to go over it again and digest it a bit more-alot to take in.

Kingtal0n:thanks for your post too and clearing that one point up. May come back here with more questions soon.