Crankcase ventilation

[turbomacncheese]

Next question: why are there so many holes in this block? I have two in each valve cover and two in the block. My donor came with a catch can (in and out) so I get to figure out how I want to route everything. I've seen a bunch of alternate competing methods on subie forums, so let me ask what happens if I do it like this?
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grey blob in the upper left is the catch can
grey rectangle is the turbo inlet soft pipe
black circles are vent tubes
blue blobs are hoses
green thing is the pcv valve
"X" means "cap this off"

Seems like this would only take "cleaned" air directly back into the intake manifold except under boost when it would go back to the intake (which I still don't like, but hey, never used a catch can before so maybe I'll be surprised).

What are the down sides of setting it up like the picture?

Thanks for this, too.

[Harley818]

Not sure where anymore, but I did some research and found that the recommended method for catch cans was to have two.
One for the vents from the heads, through the can and into the turbo inlet.
The other from the block, through the second can and into a different turbo inlet.
Thats what I did.

I went back to look at my thread but didn't see much on the catch cans. Can't believe I didn't take pics.
So I went out to the garage.... here they are....

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[mistasherm]

I just installed a two catch can set up - PCV running to one catch can and the crankcase vents running to the other. Two ports on my turbo intake are used for vacuum for these cans, one for the 3 port GS BC solenoid and the remaining one is capped. Pretty good catch can write-up on NASIOC here: https://forums.nasioc.com/forums/showthread.php?t=754710

[turbomacncheese]

Thanks. I'll check those out. I woke up this morning pretty sure that the PCV valve in my picture would function as a vacuum leak when off-boost.

[twgab]

Take your red X's and run them all together with a T fitting. these are to balance the pressure between the crank case, and the heads. In the boxer engine under boost, pressure will build in the crank case, and not let the oil drain out of the heads unless the pressure is equal between the case & heads.

[turbomacncheese]

Right, but I have TWO pipes on EACH valve cover. One set is teed with one from the crank case.

[turbomacncheese]

I just installed a two catch can set up - PCV running to one catch can and the crankcase vents running to the other. Two ports on my turbo intake are used for vacuum for these cans, one for the 3 port GS BC solenoid and the remaining one is capped. Pretty good catch can write-up on NASIOC here: https://forums.nasioc.com/forums/showthread.php?t=754710

I made it through 9 of the 13 pages so far (and a couple of red-herring links in the middle). Maybe I missed it, but I don't see any WHYs anyplace. He criticizes a couple methods (as SORTA right) but doesn't say why they are deficient. He lauds the two-can method as superior, but doesn't mention on what basis. I'm a math guy, I want a proof, lol. I think I'm not alone there, either, as repeated questions about this and the basic design of the Subaru PCV system go unanswered (so far, anyway).

Maybe I'm not as well versed on PCV in general as I thought I was.

[turbomacncheese]

From Wikipedia... https://en.wikipedia.org/wiki/Crankcase_ventilation_system

Breather[edit]
In order for the PCV system to sweep fumes out of the crankcase, the crankcase must have a source of fresh, clean air, called the crankcase breather. To achieve this, the crankcase air inlet is usually ducted to the engine's air cleaner. The breather is usually provided with baffles and filters to prevent oil mist and vapour from fouling the air filter.

Intake manifold vacuum is applied to the crankcase via the PCV valve, drawing fresh air into the crankcase via the breather. The airflow through the crankcase and engine interior sweeps away combustion byproduct gases, including a large amount of water vapour which includes dissolved chemical combustion byproducts. This mixture of air and crankcase gases then exits, often via another simple baffle, screen, or mesh to exclude oil droplets, through the PCV valve and into the intake manifold. On some PCV systems, this oil baffling takes place in a discrete replaceable part called the 'oil separator'.

PCV valve or orifice[edit]
The PCV valve is a variable orifice that controls the flow of crankcase fumes, admixed with fresh air admitted to the crankcase by the breather, into the intake tract. With no manifold vacuum, a restrictor—generally a cone or ball—is held by a light spring in a position exposing the full size of the valve's orifice to the intake manifold. With the engine running, the restrictor is drawn towards the orifice by manifold vacuum, restricting the opening proportionate to the level of engine vacuum vs. spring tension. At idle, manifold vacuum is high, but a large amount of extra air would amount to a vacuum leak, causing the engine to run too lean and/or too fast. So at high manifold vacuum, the PCV valve allows only a low flow rate. This is in accordance with the low volume of crankcase fumes generated at low engine speeds. At higher engine speeds, with less manifold vacuum, the PCV valve permits a greater flow rate to keep up with the greater volume of crankcase fumes; because of the higher engine speed, a greater amount of "extra" air via the PCV system can be tolerated without upsetting the engine's running. At full throttle, very little manifold vacuum is present, so there is little flow through the PCV valve. However, this is the condition under which the maximum volume of crankcase gas is present. Most of it escapes under its own pressure via the crankcase breather, flowing into the engine's intake tract via the air cleaner.

A second function of the PCV valve is to protect the engine in case of a backfire, which causes a sudden high-pressure pulse in the intake manifold. This forces the PCV valve closed so that the backfire flame can't reach the crankcase, where it could ignite flammable fumes and cause damage. Turbocharged engines also experience periods of high intake manifold pressure during which the PCV valve is closed and the crankcase fumes are admitted to the engine via the breather and air cleaner.

Some engines use a fixed orifice rather than a variable-orifice PCV valve.

Component placement[edit]
The crankcase air outlet, where the PCV valve is located, is generally separated as widely as practical from the crankcase air inlet. For example, the inlet and outlet are frequently on opposite valve covers on a V engine, or on opposite ends of the one and only valve cover on an inline engine. The PCV valve is often, but not always, placed at the valve cover; it may be located anywhere between the crankcase air outlet and the intake manifold.

Clears up kind of a lot. Enough here that reading between the lines is much easier.

[Blwalker105]

As an alternative, research getting rid of all the catch cans and aos systems entirely. Anything that separates air and oil is a condenser and the condensate that returns to your oil pan is not just oil, but an ugly mix of oil, water, acids and other combustion by-products. I’m liking the thought of welding in one or possibly two Vibrant Performance 11189’s into the exhaust, after the turbo, to scavenge the crankcase. Worked beautifully on my Continental IO-550 flat-6 engine.

[twgab]

https://forums.nasioc.com/forums/showthread.php?t=1977948
This may help. You should have one baffled port, and one open port on each valve cover, and one open one baffled on the crack case. the open ports should be linked together for balancing, and the 3 others are your crank case ventalation, running to a catch can or air oil separator. The older 2.0 liter heads only have one baffled port. When cornering hard under boost, oil will sometimes be forced out of the one port due to the fact that the pressure is higher in the crank case than the head. When I built my wife's hybrid motor for her 02 wrx wagon, I added an extra port on each valve cover for the balance. I have an 03 wrx without the extra port, and the catch can will have a noticable amount of oil in it after hard cornering at higher boost levels.

[STiPWRD]

As an alternative, research getting rid of all the catch cans and aos systems entirely. Anything that separates air and oil is a condenser and the condensate that returns to your oil pan is not just oil, but an ugly mix of oil, water, acids and other combustion by-products. I’m liking the thought of welding in one or possibly two Vibrant Performance 11189’s into the exhaust, after the turbo, to scavenge the crankcase. Worked beautifully on my Continental IO-550 flat-6 engine.

The aos returns the condensate back into the engine but the catch cans can be dumped out periodically.

[Hindsight]

The newer AOS devices have an input and output coolant line that heats the can up, helping to prevent condensation. The Crawford AOS has this feature. I'm running one on my 818 and really like it. ZERO oil film on any of my intake tubes.

[NateInPGH]

The newer AOS devices have an input and output coolant line that heats the can up, helping to prevent condensation. The Crawford AOS has this feature. I'm running one on my 818 and really like it. ZERO oil film on any of my intake tubes.

I'll second this - I have an IAG street AOS on my GR and it does a fabulous job keeping the intake clean.