AOS/CC discussion about air oil separators and catch cans...

[bigBADbenny]

Intro.

[bigBADbenny]

Personally, imho, on cars with dual head ports, tapping the CCV for AOS/CC is redundant.

Subaru went to huge lengths with these engines to improve the woeful oil control issues experienced in a track situation, extended high G’s leading to oil surge in the sump filling the outside corner head.

Everyone apart from Flatirons has missed the intent of the schema:

The CCV blows into the heads, via the so called balance pipes, to assist oil return to sump.

This effectively makes the CCV & heads part of the stock AOS setup, the heads forward PCV return ports being baffled.

The sump is scavenged from the breather port straight into the PCV/inlet (iirc).

So ideally the head return breathers and the sump emissions hoses will be the aftermarket AOS/CC inlets.

Subaru didn’t put a big AOS on the rear of the block for nuthin!

Anyway you heard it here first

[bigBADbenny]

The sump is scavenged from the breather port straight into the PCV/inlet (iirc).

The sump gasses leave the sump breather port (just in front of the gearbox) and go into an F-shaped splitter (with internal restrictions). See image below.



Under manifold vacuum the dirty air goes to the PCV valve on the inlet manifold.

Under manifold boost the PCV valve closes and the dirty air is drawn into the pre-turbo pipe.

Either way, the crank gas is filthy with water vapour and oil that I would rather catch (most of) before it goes into the manifold or the pre-turbo pipe. That's why I put a catch can after the sump breather port and before the splitter.

[Some people only care about gunk in the intercooler, so they insert the catch can on the pre-turbo pipe side of the splitter and let whatever rubbish directly into the manifold.]


I can't claim to fully follow your explanation above (diagrams & exploded images usually help my understanding of all this hose routing) but I see plenty of value in adding a catch can after the crank vent just based on the rubbish I collect from that spot.

[bigBADbenny]

Thanks Yowie for the pic and info.

Where did you find that photo?

Its a fiendishly complex system but the spaghetti is slowly unravelling.

My point of view is that subaru made the CCV push blow-by into the heads for a reason and I think it’s oil control related.

To me, the crankcase, sump and valve covers are all part of the same environment, there’s not more or less water, goo, varnish in any particular area because they’re all connected.

Iirc there is an oil drain gallery from valve cover to crankcase to the sump.

I really want to map out the stock systems to see how subaru has developed and refined the pcv system.

I did see that usdm my15 sti has at least 3 of the blow-by sensors!

[Yowie]

Excellent. Should be an interesting thread (for those of us that like crank case grot anyway).

Here is another cardboard-assisted diagram explaining the crank catch can routing on my car:



I have since removed the 6mm restriction on the pre-turbo-pipe line in an experiment.

[bigBADbenny]

Love it
Its a trend iirc, that most dual catch can setups never catch anything from the heads.

So I’m thinking, why catch a bunch of crap via the CCV when the aim is to keep blow-by out of the inlet tract?

[Yowie]

The OEM restrictions in the F-shaped splitter are shown below:





My theory is that a new stock engine has those restrictions as:

(a) a further baffle to keep oil in the crank (and only let gas out); and

(b) in terms of the pre-turbo pipe, perhaps a restriction to that (under manifold vacuum) the PVC draws more gas from the crank than from before the turbo.

I'm not sure about (b) but I don't think it's a big problem to omit the restriction. Since the crank is under mild pressure and the pre-turbo pipe is under mild vacuum there should be a natural bias for the crank gas to be drawn into the PCV.

For higher boost performance cars the accepted wisdom seems to be "you need big enough hoses to deal with the blow-by" and I have never seen any reference to deliberate restrictions.

[Yowie]

Love it
Its a trend iirc, that most dual catch can setups never catch anything from the heads.

So I’m thinking, why catch a bunch of crap via the CCV when the aim is to keep blow-by out of the inlet tract?

The image below shows the different content collected out of the catch can for my:-

(a) rocker covers (after the balance pipe, before the pre-turbo pipe) left; and

(b) crank case right

Bear in mind this is on E85, before I changed oil types to reduce that "butter" formation.

When I was on petrol your original statement was correct (stuff-all caught from the rocker covers). On E85 it collects a lot of water vapour (along with some oil), especially in winter.




---

In terms of

why catch a bunch of crap via the CCV when the aim is to keep blow-by out of the inlet tract?

, my thoughts are:

(i) The Crank Case Vent sends gas through the F-shaped splitter, which sends dirty air to the pre-turbo pipe under manifold boost conditions; and

(ii) There must be some value to keeping muck out of your inlet manifold too. On a direct injection vehicle (not an EJ25) it would help keep the valves clean. On a port-injected EJ I still think it's worth keeping the PCV clean, not allowing puddles of crud to build up in the manifold etc. even if, at the moment of entry to the manifold you are under vacuum conditions and unlikely to knock.

Upper Engine Cleaner exists because a clean manifold is a good thing.

Each to his/her own of course.

[Yowie]

Positive Crankcase Ventilation (PCV) valve

For those who have not seen a PCV valve, see below (clean and dirty).

One end threads into the back of the inlet manifold, the other end is a large barbed-type fitting.

Inside is a little "pill" that floats freely.

Under vacuum the pill is sucked towards the threaded end/manifold, allowing air in.

Under boost the pill is pushed towards the barbed end/firewall, blocking off the manifold and forcing the crank gas to travel down the alternative route to the pre-turbo pipe.






They clean up pretty well with "Throttle body & carby cleaner", which seems to be nasty stuff so wear gloves.

[bigBADbenny]

Absolutely! This is technical discussion regardless.

Marcuses car had a really clean PCV, but it had varnish just around the inside of the flange in your pic, enough to make the pcv stick shut.

Before committing to any AOS/CC setup, I did the usual research on various setups: primarily the single can w/ pcv delete and dual can w/ pcv intact.

As regards the latter, I couldn’t work out the simplest setup for a stock tmic car.
Simple meaning effective but also efficient and not restrictive.

So I concentrated on fixing my inlet tract & crankcase leaks and wow, excessive oil residue in the inlet wasn’t even an issue any more.

Which lead me to think the stock PCV system is fine for a mildly tuned stock car, assuming no inlet/crankcase/valve cover leaks and regular maintenance.

However it’s still an interesting subject and I’d definitely like to nail a dual can solution.

Which means very thoroughly mapping the stock pcv system.

[Yowie]

...various setups: primarily the single can w/ pcv delete...

I have not heard of this. Can you elaborate? Is it as simple as running a valve covers catch can and blocking all ins and outs related to the crank breather & PCV?

(if it's in the early post I didn't understand - sorry about that, I'm a bit hard-of-understanding without diagrams or hands-on experience for these things).

Which lead me to think the stock PCV system is fine for a mildly tuned stock car

Sure. As is not using catch cans at all.

The whole "do I need this supporting mod?" question depends on too many factors.

Personally, I'm a tinkerer who likes the idea of the inlet path being as clean as it can be, so I run dual catch cans. Unfortunately my catch cans are not 100% effective at filtration (or something else is going on) because there is still fluid in my intercooler and a little pool of oil in my throttle body hose.

In terms of nailing a dual catch can solution, I think it comes down to:-

(a) intercepting the two factory exit points for oily gas (crank and valve covers) with a catch can each, then running them to their factory sources of vacuum; and

(b) physical issues such as what size can will fit in what space and how to route hoses (in, out and drain).


In relation to (b), I'm surprised that the passenger side strut tower (under the wiring loom connection) isn't a more popular spot for a catch can on Subarus. Do foresters have more room there than Liberties and WRXs or something?

[bigBADbenny]

Yowie is off to a great start with his years of experience in building a better mousetrap

Let me explain my theory about the stock PCV system.

Beginning with the crankcase vent vacuum hose:

That’s it in the Cooling section on opposed forces:
http://opposedforces.com/parts/legacy/e ... tration_2/

Here in parts useage we see it’s common to BP/BL GT, SH XT and GR WRX.

http://opposedforces.com/parts/info/99071AC220/

Meaning we’re talking 07+ ej255.

Its in the cooling section because it shares a cooling system pipe.

[bigBADbenny]

Ok, so this is the Carter Ventilation section on OF.
http://opposedforces.com/parts/legacy/e ... ntrol_pcv/

You can clearly see the CCV vacuum hose feeds the rearward breather ports on the heads, the join is at the wee nubbin on the rear of the balance pipe.

Also note the internal diameter of the “heads balance pipe” from CCV to heads remains consistently large, meaning the crank case blow-by has a favourable pathway.

Effectively, this pathway is split between the oil return gallery/s in the heads and the only other exit, the forward baffled heads breather ports in the valve covers.

[bigBADbenny]

Reserved

Well, now we move on to the inlet manifold and turbo section where things get really tedious, my phone starts to die and my eyelids droop

http://opposedforces.com/parts/legacy/e ... tration_2/

Yes, because this is properly the PCV & inlet returns. It might as well be spaghetti but it shall be unraveled!

So anyhow, this end of the system is generally smaller diameter...

On the far left the brake booster hose can be seen above the 3 way hose assy that Yowie mentioned above.

On the far right is the the part in question is Hose assembly-master back, 11861AA020, aka sump breather hose, aka sump emissions hose.

This hose is hooked to the sump breather port, which leads to the air oil separator on the rear of the block, which is fed, via an o-ring, from the right rear corner of the sump.

As Yowie pointed out, the vacuum drawn from there is probably minor.
Flatirons speculated the port is to help oil control in the sump and potentially help the pickup to remain covered in oil.

[bigBADbenny]

...various setups: primarily the single can w/ pcv delete...

I have not heard of this. Can you elaborate? Is it as simple as running a valve covers catch can and blocking all ins and outs related to the crank breather & PCV? ...

Yes a single can w/pcv delete is blocking/deleting everything stock bar the rearward heads balance ports and CCV, and running the 3 sources to a single can with vent to inlet or ( ) air (or exhaust)