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Discussion Starter · #1 ·
on a 2.5 turbo, common block, stock:

where does the fresh air come in for the PCV system?

i keep reading that other pcv systems on turbo cars have some SECOND tube on the crankcase somewhere which goes to some filtered atmospheric air source, so that when vacuum is applied to the PCV port on the valve cover, fresh air is sucked through the crankcase to carry all the crap gases out.

seems to me the 2.5 turbo engine is sealed tight except for the ONE port on the valve cover...is this the case?

does it have to do with the little "t" on the turbo drain tube?

if so, what am i supposed to do if i have a hybrid turbo that doesnt have that T!
 

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The stock turbo fresh air intake is the T rubber at the PCV outlet of the valve cover, the top goes to PCV valve and the bottom goes to to the air box to get fresh air.

If you want two PCV in/out lets, get a TBI valve cover and the oil splash shield underneath it.

 

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Discussion Starter · #3 ·
correct me if im wrong, but i think the tube going to the airbox (on the turbo, as you mention) is for vacuum when under boost and is not for fresh air, as there would never be positive air pressure at that point anyways.

im starting to think that the turbos just dont HAVE a fresh air system, and that all they do is SUCK air from the crank case and never blow air THROUGH IT
(and then suck it)
 

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The turbo PCV design was poor, that's why I have a TBI valve cover on my car now.
So the in/outlet in the middle you put a pcv valve on and connected it to the manifold vacuum? And the in/outlet at the driver's side end you connected to the air box or small filter?
 

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I just said screw it and put a lil air thing on the tube and let it vent crank case pressure then plugged the manifold vacuum. It works well enough
 

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That's how I've had mine, but doesn't it leak vacuum though? When I put my finger over the driver side outlet, it sucks my finger with increasing force. Is that vacuum from the manifold?
 

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All vacuum is from the manifold. :)
Well duh. I was asking whether that suction was vacuum from the manifold or perhaps crankcase suction. Because the way I see it, you connect the manifold to the valvecover and then have a hole on the other end of the VC, that's like having a huge vacuum leak. :confused:
 

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The theory behind PCV operation is this, A hose from the intake manifold goes to the PCV valve. The PCV valve usually sits in the top of the valve cover. Then another hose comes from the air filter housing, either from the inside of the air filter or through a breather filter, and to the crankcase. Now when the engine is running air is drawn from the air filter housing into the crankcase, through the PCV and into the intake. So there is a vacuum inside the crankcase. If you take the oil fill cap off, air will enter. This is normal.
http://www.filtercouncil.org/techdata/tsbs/94-2R1.pdf
 

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correct me if im wrong, but i think the tube going to the airbox (on the turbo, as you mention) is for vacuum when under boost and is not for fresh air, as there would never be positive air pressure at that point anyways.

im starting to think that the turbos just dont HAVE a fresh air system, and that all they do is SUCK air from the crank case and never blow air THROUGH IT
(and then suck it)
I guess... you must be correct because there is no other way for fresh air to get into there, other than through the intake manifold and past the pistons.

Under heavy engine load and high RPM, positive crankcase pressure is at its highest, and since there's no manifold vacuum under heavy throttle (especially in forced induction applications), that crankcase pressure has to be able to go somewhere, and I'd prefer it not to go out the seals of the engine. I always thought that is why there is a hose running from the valve cover to the air box. In theory, there is a small vacuum between the air filter and throttle body/turbocharger under these conditions, so that will be where the positive crankcase pressure will be vented.
 

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Where is our resident engineer?
Now I am getting confused.
What I am reading goes against all theroy of how an internal combustion engine operates. An engine is nothing more than an "air pump" and it operates on the theroy that high pressure moves to low pressure to equalize.
Atmospheric pressure is higher than the pressure in the manifold so as the throttle is opened air rushes in to equalize the pressure behind the throttle plate.
An engine's CID is how much air it can hold, once that threshold is reached RPM and power are maxed out, that is the problem with internal combustion engines, they are not efficiant and use up thier air supply before thier fuel supply, that is why tuned manifolds, multi-valve and vvt are so useful and why nitrous is so effective.
The turbo compresses and forces(raises pressure above the valve) in more air than the engine would normally draw in on its own.
If the airbox becomes pressurized from boost(above atmospheric) then total engine pressure is now higher than atmospheric which would lead you to believe, by theroy that now the air in the engine will now try to escape to the atmosphere to equalize, so no air will enter the engine which means that everytime you enter boost the engine would stop running.
A N/A car at WOT still has slight vacuum.
Somewhere in the air intake system there has to be a lack of pressure so outside air will still enter the engine or turbo's and superchargers will not work.
In summary when at high rpm and boost injector pulse width is increased for the extra amount of air which has to enter thru the airbox and intake.
 

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That is what I was thinking, actually I never even thought about this until it was brought up in this thread.
The airbox cannot be under the same pressure as the intake then,there are numerous hoses that are not clamped and would be blown off everytime you went into boost, and that is what this discussion is about.
If nobody comes up with a concrete answer I will bring it up the next time I am at Chrysler training although I have to say me and the instuctors do not always see eye to eye on principle and theroy of operation.
 

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Discussion Starter · #17 ·
okay back to the original question people: WHERE is this connection from the air cleaner to the crankcase??

on the 2.5 turbo is it the teed-off tube on the oil drainback tube? i think it is...can someone confirm this?

how am i supposed to duplicate this with a hybrid turbo? make a tee?
 

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From just under the PCV valve, there is a hose connected to the air box, this is where the fresh air goes in.

90+ TI air box is different than pre TI 90+ air box.

90+ TI turbo have a tee on the oil drain back. I don't think it's a good design. If I were you, I'd cap off the oil in the air box for smog, and run a catch can when you're done with smog.
 

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Discussion Starter · #19 ·
right, i know which tube you are talking about, but it doesnt make sense that its the fresh air SOURCE, for "fresh air cleansing" there need to be two "tubes" on the "crankcase system", one with suction, one connected to ambient. the tube you are talking about is used for suction (whatever is available in the air cleaner box, which could be significant since we are under defacto boost and sucking in a lot of air) when the manifold is under boost (which closes the other side of the pcv valve).
 
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