Help me understand how the PCV system works.

vrg3 · Post by **vrg3** » Mon Nov 22, 2004 9:39 pm

Hehehehe... Yeah, but isn't the volume of gas flowing out the exhaust much higher than the volume flowing into the intake?

Is the goal just to pull a vacuum on the crankcase breather? Because maybe a small vacuum pump, like the kind used on a lot of diesel cars, would do the job. The pump could suck through a catch can and have its exhaust go into the intake before the compressor.

Hmm. I think Jason Grahn brought that possibility up once before.

It is convenient, though, to take advantage of vacuum sources that are already on the car.

professor · Post by **professor** » Mon Nov 22, 2004 9:44 pm

Yeah, huge high boost drag race motors have vacuum pumps / separators but I would think that is overkill for street applications.

The connection to the exhaust makes sense versus catch pots, it would assure burn-off if located properly on the hot exhaust pipe, and no maintenance.

azn2nr · Post by **azn2nr** » Thu Nov 25, 2004 1:43 am

for the people who need to re do the pcv where the f piece is you need 3/4 5/8 and 1/2 hose and a 90/90/90/90 corner cube 3/4 nylon barb and 3/4 to 1/2 barb reducers and hose clamps

Impregacy · Post by **Impregacy** » Thu Mar 24, 2005 6:08 am

Could someone point out where the f peice is on the diagram because i'm a little unclear as to what the f piece is but...

after reading this whole thread and investing a lot of consideration into the diagrams and PCV system's purpose. My theory about the subaru's PCV sytem is that it was not designed well for turbo-charged engines where the intake manifold regularly sees positive boost pressure that forces the PCV valve shut. How do i know that positive manifold pressure forces the valve shut? Easy, i took it off the engine, held it in my hand at the appropriate angle and tried to blow through it. (mmmm... hydrocarbons). Even my slightest baby breath would force the valve shut.

That being said (and proven in my lab) take a look at what i think happens to the crankcase's pressurized oily gases when there is boost pressure holding the PCV valve shut.

http://img71.exs.cx/my.php?loc=img71&im ... sed5cc.jpg

So i THEORISE that is what happens when the turbine is boosting. Does this seem right?

Also from what is written in this thread i gatherd that the PCV valve is too closed when there is excessive vacuum in the intake manifold as for example when the throttle plate isn't open very much at idle or little throttle. I confimed this in lab tests by sucking hard, oh yeah, on my PCV valve.

So on a turbo car i think there may be only a small window of throttle angles where the vacuum is just right for opening the valve and sucking in the oily crank case vapors. The rest of the time the crank case just releives itself into your intake -upstream of the turbo.

As for the position of an oil catch-can i would give two recommendations:

1. If your only goal is to stop the oil from getting into the intake BEFORE the turbo and therefor stop it from getting into your intercooler ect... i would put the catch-can here:

http://img154.exs.cx/my.php?loc=img154& ... an17sv.jpg

this way you can still say you are friendly to the environment because the PCV system would still work in that narrow window of throttle angles

2. If you say "screw the environment, who cares?" then maybe just put the catch-can here to stop all of the oil close to it's source.

here: http://img100.exs.cx/my.php?loc=img100& ... opy7fw.jpg

I've not tested these location yet in my lab so it's just my two cents until i can get my engine running.

Edit: Actually if you wanted to stop all of th oil you would have to install another catch-can between the valve covers and the turbo intake as well as my #2 recommendation. As a matter of fact i found that most oil catch-cans come with instructions telling you to put them between the valve cover and intake -but i think on the EJ22t it can come from both pipes.

So this guy might have the right idea installing two http://www.scoobymods.com/forums/archiv ... -3346.html

here is a link to a WRX install where i believe oil is only being intercepted from the valve covers: http://www.scoobymods.com/forums/showth ... readid=693

Here is an install for on DSM that might have relavent info: http://www.roadraceengineering.com/inst ... ctions.htm

here's my new prototype setup that i think should be better than my first two: http://img176.exs.cx/my.php?loc=img176& ... lan4rm.jpg

TDGKORN · Post by **TDGKORN** » Thu Mar 24, 2005 5:37 pm

I made and installed a catch can on my car last weekend.

I haven't checked to see how much (if any) oil has pooled up yet.

Here are a few pics.

Its made of a air compressor filter. and mounted where the ac evap thingy was.

I tried the same setup except had the hoses connecting the top part of the F pipe and where it ties in to the intake. That setup resulted in no oil in the catch can. So I moved it.

I'll let everyone know if this setup works or not.

Troy

vrg3 · Post by **vrg3** » Thu Mar 24, 2005 6:06 pm

I don't follow, Troy... You just put the can between the two things on the tee there? But those two aren't normally connected by a hose. The one pointing the passenger side is meant to connect to the passenger side valve cover, and the one pointing towards the back is meant to go into into the intake.

I see you plugged the fitting in the intake that's supposed to supply fresh air to the valve covers... did you also just cap off the fitting on the passenger side valve cover?

Wouldn't this just make the whole thing not work right?

TDGKORN · Post by **TDGKORN** » Thu Mar 24, 2005 7:14 pm

My reasoning behind my placement is when looking at the all the pcv hoses these one had the most oil in them.

It is experemental. I am in the process of finding the right combination to hoses and such.

I have read all the post's and noone has come to a conclusion, so I thought I would stop talking about it and start tring things.

When I find something that works I'll let everyone know.

Troy

vrg3 · Post by **vrg3** » Thu Mar 24, 2005 9:53 pm

But you've changed the topology of the system...

What did you do with the fitting on the passenger side valve cover?

TDGKORN · Post by **TDGKORN** » Thu Mar 24, 2005 9:58 pm

I think you are missing something.

Both valve covers are connected to the black tee thing. From there the hose goes to the catch can instead of dumping into the boot b.
The out of the catch can then goes to the boot b.

Does that make any sense?

professor · Post by **professor** » Thu Mar 24, 2005 10:00 pm

it probably had the most oil because the condensed oil ran down to the bottom-most place and puddled there

The only way to find out for sure what is going on would be to punch little holes in the lines and hook a manometer to see what the pressure is, under various conditions.

TDGKORN · Post by **TDGKORN** » Thu Mar 24, 2005 10:06 pm

My point about the oil was that there was oil in the hoses and not just the tee. Which would lead me to believe that oil is coming from the valve covers to the boot B.

The tee in boot B is the furthest down stream of the fittings that are in the intake tract(that are part of the pcv system). So no oil could be going from the intake to the valve covers from there. The oil must be coming from the valve covers.

vrg3 · Post by **vrg3** » Fri Mar 25, 2005 12:00 am

Oh, I see now, Troy. Sorry... the pictures looked like something different before.

TDGKORN · Post by **TDGKORN** » Fri Mar 25, 2005 12:02 am

Yeah, the angle of the pics are wierd.

Impregacy · Post by **Impregacy** » Fri Mar 25, 2005 4:09 am

so you're saying that most of the oil/vapor is coming from the valve cover's vent and not the crank case vent?

THAWA · Post by **THAWA** » Fri Mar 25, 2005 7:13 am

I finally took a second to read this thread.

Vikash, the closed deck of the block should have no effect of the blowby. The only part that is different between a closed and open deck is the water jacket. The oil drain is the same between open or closed. And this is the only part that effects blow by right?

The wrx uses a different setup than us in that there is not a "t" connecting the block and the heads:

You can see all the other parts of it though if you remember the turbo inlet is different

Maybe the reason there is a T between the heads and crankcase is so that there is still a pattern of flow the blowby can follow when the pcv valve is closed instead of backing up into the valve cover vents?

Though that doesn't really make sense now that I think about it...

vrg3 · Post by **vrg3** » Fri Mar 25, 2005 7:31 am

I dunno... Isn't the WRX motor open deck?

THAWA · Post by **THAWA** » Fri Mar 25, 2005 8:26 am

Okay maybe it's something else then. Doing some searching, and the EJ20G (at least the legacy/liberty) doesn't have a pcv connection between the heads and the crankcase. But the EJ257 does have a pcv connection between the heads and crankcase.

vrg3 · Post by **vrg3** » Fri Mar 25, 2005 8:54 am

I was pretty sure the EJ20G did have that connection...

The EJ257 is semi-closed-deck, right?

Post by **Legacy777** » Fri Mar 25, 2005 4:07 pm

Yes the EJ20 WRX motor is open deck

Yes the sti EJ25 is a semi-closed deck

I don't see how the configuration of the deck would have any barring on the PCV system.

THAWA · Post by **THAWA** » Sat Mar 26, 2005 2:35 am

The FSM for a 92 JDM/ADM Legacy doesn't have that in the pcv diagram for the EJ20G.

vrg3 · Post by **vrg3** » Sat Mar 26, 2005 4:43 am

adam|RSLC| on the RS Liberty Club forums seems to refer to it:

adam|RSLC| on rslibertyclub.org wrote:In the RS you will find that on the top of your rocker covers there are 2 breathers ... These 2 breathers actually merge into one pipe which is located under the inlet manifold just behind and to the left of the power steering unit

We should get Matt Monson or someone else with firsthand experience playing with EJ20Gs to resolve this question. Matt?

THAWA · Post by **THAWA** » Thu Mar 31, 2005 6:03 am

Okay, I think that what I said before actually does make sense. It would seem like the t-section acts sort of similar to how the bpv works in the intake system. If I understand that system correctly, the bpv sends excess boost back into the intake when the throttle plate isn't open large enough to flow the air. I assume the t section sends excess blowby back to the heads when the pcv valve isnt open large enough to flow the blowby. Does that make sense?

NICO · Post by **NICO** » Thu Mar 31, 2005 11:54 am

it does make cents.

now what if you disconect it from the intake stream, an let it go in a catch can and be on a free open air filter?

dzx · Post by **dzx** » Thu Mar 31, 2005 12:11 pm

NICO I WRX U wrote:it does make cents.

Trading words like that drives me nuts for some reason.

vrg3 · Post by **vrg3** » Tue Apr 05, 2005 6:46 pm

Hardy - I dunno... I thought the area behind the valve covers is supposed to be pretty much continuous with the area in the crankcase, isn't it? I mean, don't a lot of inline engines have their PCV stuff only on the valve cover, with no fittings on the block?

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Help me understand how the PCV system works.