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Old 04-24-2009, 03:59 PM   #26
Steelworks
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Originally Posted by LetItSnow View Post
Using a breather creates an opening in the system that makes your air meter incorrect - it properly measures its intake at its location, but not what actually enters the cylinder heads. The amount of difference is questionable, but it's guaranteed.
the air entering the heads is post filter, and MAF. So it is indeed metered air.
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Old 04-24-2009, 06:44 PM   #27
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Quote:
Originally Posted by Steelworks View Post
the air entering the heads is post filter, and MAF. So it is indeed metered air.
OK, I'll fix this for you:

Using a breather filter creates an opening in the system that makes your air meter reading incorrect - the MAF properly measures the air that passes it, but that's not the volume that actually enters the combustion chambers.
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Old 04-25-2009, 12:31 PM   #28
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your pcv is post combustion .
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Old 04-28-2009, 06:40 AM   #29
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Originally Posted by LetItSnow View Post
OK, I'll fix this for you:

Using a breather filter creates an opening in the system that makes your air meter reading incorrect - the MAF properly measures the air that passes it, but that's not the volume that actually enters the combustion chambers.

Sorry... I totally jumped the gun. Didn't see the part about a breather filter. oops
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Old 05-27-2009, 12:40 AM   #30
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Another reason not to remove the PCv valve is that if you remove the valve and block the PCV valve connection, you aren't actually ventilating the crankcase with fresh air. Remember that blowby gasses contain water vapor, Hydrocarbons and NOx. The water vapor and NOx degrade the oil much faster if there is no PCV valve (or orifice) to continually purge these substances from the crankcase (whenever your throttle is not wide-open). Your oil will sludge up and oxidize much faster without a PCV valve. Also the HC's in the blowby gasses are fuel that is best burned in the combustion chamber rather than just wasted.

Dave
Thanks for your contributions to this thread. Very informative!!!

What do you think about air/oil separators in general?

In particular there is one product - IXIZ that retains the stock PCV valve (on turbo car), so function under light throttle and intake manifold vacuum will be retained. However under boost the vacuum from intake inlet goes via the separator, so oil is caught there.

Sorry for bit of a thread hijack....
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Old 05-27-2009, 10:19 AM   #31
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You can just install a catch can...
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Old 04-11-2010, 06:44 PM   #32
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Bringing this one back from the dead since it's been nearly a year since it was started. The whole catch can / air-oil separator thing is something I've thought about doing to each of my cars for a while and have never actually gotten around to doing.

So I was looking at how PCV/breather setup is arranged, and it seems a bit different than what was originally posted here. My understanding is that the newer cars (not sure what "newer" actually means) have the PCV valve located on the top of the block, below and to the left of the throttle body (as you're facing the engine from the front of the car). Is that correct?

On my EJ25D, the PCV valve is on the intake manifold. The PCV line runs from the PCV valve to that same spot on the block where I think the newer cars have the PCV valve located. Coming out of the crankcase, though, there's a Y - 1 hose goes to the PCV, and 1 goes to the intake (in the stock configuration it went to the torque box). So, I re-drew williaty's original diagram to show how mine is set up:

I put ???s next to the hose that is "extra" on my setup.

And here's a picture showing the various lines (can't see the Y at the top of the block, though - it's under the IAC, which is under the PCV).


So, I'm pretty good on how the PCV operates. But I'm confused about the purpose of the "extra" hose that runs from the top of the block/crankcase to the intake. At high load, with the PCV shut or nearly shut, the extra hose would provide an extra path (in addition the VC breather hoses) to port the blow-by gases back into the intake piping and then into the combustion chambers, so that makes sense. At low load, though, with the PCV in some sort of open position, it seems like the PCV would be sucking from both the crankcase and the intake, which doesn't make sense.

As far as I know there's no check valve in the Y that comes off the top of the block, but I guess I need to check that just to be sure. And as far as I know I have the various hoses hooked up correctly - I seem to recall with the stock intake, there were 3 connections on the torque box and 1 on the bottom of the intake tube. Later this week I'll probably be hitting the junkyard, and last time I was there they had a number of late 90s Legacys/Outbacks, so I can take a look at those to verify what I remember and verify the hoses are all supposed to route back to the intake tubing.

Any thoughts on that extra hose?
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Old 04-11-2010, 08:57 PM   #33
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Well, one thing I noticed, the PCV will be open, always. It doesn't shut at high load. The pressure in the crank case will always be higher than the pressure in the intake tract so long as the engine is open. Does that change your thinking any?
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Old 04-11-2010, 11:27 PM   #34
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Well, not really. When the PCV valve is closed (hypothetically) the flow paths all make sense. When it's open, I don't understand what the hose from the crankcase to the intake is doing, since it would seem that is allowing air to bypass the throttle plate by way of the Y that connects the crankcase hose and the PCV hose together.
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Old 04-14-2010, 09:31 PM   #35
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Pat,

At least for the older cars, this is how the PCV system is supposed to work according these posted diagrams.

http://www.rs25.com/forums/f5/t10327...ml#post1648612

In short, that 'extra' port brings in fresh air at part throttle and acts as an additional vent at full throttle.
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Old 05-11-2011, 08:29 PM   #36
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I'm not one for bumping an old thread, but this one I found particularly usefull. Also given that I've seen some more recent informative posts from Williaty on this topic, perhaps he wouldn't mind updating it with his current understanding?
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Old 05-11-2011, 09:28 PM   #37
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I disagree, only b/c someone has to
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Old 05-11-2011, 09:44 PM   #38
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I've been informative? Dammit, I was trying to avoid that.

What is it you'd like to know?
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Old 05-12-2011, 06:10 PM   #39
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I was wondering if you had any further understanding of the Pcv valve and it's usefullness beyond what was posted in the thread? Also I found this from a link when searching for info on catch cans and their usefulness on N/A cars. This was after I read your posts about the problems with the grimmspeed a/o separator (and any for that matter) on naturally aspirated cars. The strange thing I've found is that other horizontally opposed NA engines all come with some sort of aos. The boxter/911 does as do aircraft engines (or they vent to open air).
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Old 05-12-2011, 06:39 PM   #40
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The PCV valve just seems to function as a flow rate limiter, not as an actual check valve.

Yes, boxer engines, regardless of who makes them, seem to have blow-by issues and need AOSes. Correct, the AOSes designed for turbo Subarus won't work properly on NA Subarus. To my knowledge, no one makes an AOS that works properly with an NA.
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Old 05-12-2011, 08:23 PM   #41
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Quote:
Originally Posted by williaty View Post
The PCV valve just seems to function as a flow rate limiter, not as an actual check valve.

Yes, boxer engines, regardless of who makes them, seem to have blow-by issues and need AOSes. Correct, the AOSes designed for turbo Subarus won't work properly on NA Subarus. To my knowledge, no one makes an AOS that works properly with an NA.
Well that should mean that ALL of us should be forced induction, right....
Anyway, good info.


~Josh~
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Old 05-13-2011, 10:24 AM   #42
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If the PCV valve baffles you, how about the AOS?

The only thing I can compare them to is raking the leaves in your lawn.

Stock - Bring the leaves into your house and burn them.
AOS - Collect up all the leaves, then scatter them back over your lawn.
Catch can - Bag up the leaves and the town collects them at the street.

There's a lot of crap that comes through these hoses that I bet a lot of people aren't even aware of. It's more than oil and air - a lot of it is water.

Sure, the upshot of an AOS is that you don't get heaps of oil in your intake/intercooler/etc., but the cost is that you don't evacuate the water and assorted contaminants that are in the crankcase that you would with the stock setup.
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Old 05-13-2011, 03:53 PM   #43
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AOS is more like an automated robot that gathers the leaves up and puts them in the mulch pile for you.

With the AOS, you return the same amount of crap that you would through the PCV system. The PCV system returns to the intake tract in our cars. So you're just dumping that contamination you're worried about right back into the engine anyway.
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Old 05-13-2011, 04:09 PM   #44
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I'm leaning towards a catch can, likely a Saikou Michi one.

That being said, I know Williaty you were looking into an AOS for NA but I read in a thread that you no longer needed it because you now has rings the fit properly, did you get a new motor or rebored? Also it looked like it had been some time since you've done it and you seem to drive your car hard, has the blowby oil past pcv valve issue returned? And if so did you do anything to resolve it?

Here's Porsches inexpensive N/A solution to it: http://www.autopartswarehouse.com/de...=ganfeed&gan=1

But apparently they fail... might be more reliable than the PCV valve itself though. They say they last 60K miles.

Last edited by evilWagon; 05-13-2011 at 04:20 PM.
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Old 05-13-2011, 05:11 PM   #45
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Re: AOS

Anybody who wants to dump this junk (the contents of my two catch cans, albeit supercharged) back into their crankcase over and over is more than welcome to, but I sure wouldn't.
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Old 05-13-2011, 10:10 PM   #46
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That's a whole lot of water and a little bit of oil residue.

The water will mostly blow through the AOS and pass through the engine and out the tail pipe just like in the stock system. The oil residue will be coalesced and returned to the oil system rather than coating the inside of your intake tract. There's nothing harmful there that your engine can't deal with without any problem.
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Old 05-13-2011, 10:50 PM   #47
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Interesting topic. I know when I transplanted the SRI from my old 99 lgt to my 06 2.5 (now in hybrid form), there was a definite distribution of oil/carbon/moisture streaking toward the intake manifold from both of the valve cover bungs in the aluminum intake tube from the 40k miles I put on the lgt before the swap. My guess would be that at whatever conditions that provide a negative pressure situation, it helps to act as a "junk re-circ" to the intake. I guess it would be designed as an emissions recycler of sorts for the hot, wet, slightly fuel rich debris that finds it's way back throughout the system from the valve covers back into the engine. Just a guess though... I wish I would have cleaned all of the stuff out before I installed it on my 2.5i so I could have a comparative look at what was re-circed from this engine to see differences between the 2 engines. Interested to see more input on this topic. I remember hearing that this "junk" is better off being vented/filtered that recirculated, but venting to atmosphere will also act as a vacuum leak to the system ending up in a lean (or more specifically "less rich") mixture entering the cylinders working against the MAF sensor's job. Again I may be completely off on this, but this is what I imagine is going on. Maybe in-line filters between the valve cover vents and the intake tube would be ideal?
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Old 05-13-2011, 11:50 PM   #48
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What about venting the valve covers to atm with a breather filter
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Old 05-14-2011, 10:27 AM   #49
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Quote:
Originally Posted by RaceFaceXC View Post
What about venting the valve covers to atm with a breather filter
In most cases the valve cover vents are drawing air int the crank case. As mentioned halfway through this thread that's all metered air so allowing fresh atmospheric air in through the valve covers and eventually into the intake plenum would cause the engine to run lean to varying degrees. And in the case where the air is flowing out the valve cover vents you'd foul your filter. It seems like oil catch cans are the answer though they have to be emptied manually. All that being said you can still be loosing oil from the crankcase past the rings on the piston and directly into the combustion chamber. What I'm a little bit confused on is how Porsche solves this problem on a similar engine with an inexpensive ao separator?
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Old 05-14-2011, 11:08 AM   #50
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how does the air from inside the valve cover get to the intake plenum with the lines to the intake removed?
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