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

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Re: AOS/CC discussion about air oil separators and catch can

Postby bigBADbenny » Sun Nov 22, 2020 1:14 pm

So for clarity's sake, I'm going to refer to the CCV in the middle of the block as the CCV/balance vent.

And the block port that feeds the PCV as the sump breather vent (SBV?).

Unless you or the Perrin guide has a better solution.
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Re: AOS/CC discussion about air oil separators and catch can

Postby Yowie » Sun Nov 22, 2020 1:19 pm

Sounds good to me.

Too many acronyms can be confusing though (even though I have said "PCV" a lot like a total hypocrite). If you're doing a round of editing perhaps consider using the long-form of each expression at least once per post.

(Not being a smarty-pants here)
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Re: AOS/CC discussion about air oil separators and catch can

Postby bigBADbenny » Sun Nov 22, 2020 1:20 pm

Yowie wrote:
(1) So the valve cover breather baffles must be there to prevent oil surging out of them and into the inlet.


Almost certainly. There are also baffles inside the engine just before the crank vent for the same reason.


AOS on the rear of the block indeed for the sump breather vent.

Yowie wrote: The idea is to deal with blow-by gas but keep the oil in the engine as much as possible. Obviously these baffles and even my catch cans are not perfect funk filters or some oil wouldn't be present on the "clean side" hoses after my catch cans.

I wonder how many efficient catch cans in series it takes to remove all oil residue & water vapour? It's a shame Mythbusters are not going anymore.


The simple answer is Provent filtered catch cans, but at what expense to PCV system efficiency?


Yowie wrote:
(2) I guess all the different hose sizes and restrictors in the system help to create a pressure differential in the PCV system with the majo vacuums being drawn at the PCV return in the inlet and the actual PVC valve in the intake manifold.


I would think so. I'm still intrigued by the factory restrictions in the crank F-shaped splitter and what is best practice (factory/some/nil restrictions) for a warmed-over road car. There are too many variables for my experiments to yield any answers.



(3) Another thread on LGT mentions that the heads/CCV balance pipe runs alongside the turbo coolant hose supply pipe in order to help evaporate sump condensation...


Interesting. That makes sense. Sump water vapour is a really big deal on E85 but still a factor on petrol (especially for "cold start 2 min drive to train station" usage where it can't boil off).

This is why I am not a fan of "drain back to sump" catch can setups, even if heated by coolant water. A trickle of liquid water into the sump (eg on cold start) cannot be a good thing. Andrew Hawkins of the Motive videos reports no issues with drain-back catch cans on E85, so I'm probably wrong to be such a sceptic.


(4) To add to the complexity, there's also the loose-built engine factor.


Yep, more blow-by.

A lot of those drag & dyno competition cars just vent-to-atmosphere from the catch can on my understanding. Probably better for their application for a lot of reasons including octane preservation under maximum effort runs.

Yet pulling a crankcase vacuum yields HP gains?


(5) Would be interesting to use a PCV as a one-way valve on the cam cover breather return.


Preventing which direction of flow?

On a related note, I'm interested in using a OCV on the hose between the pre-turbo pipe and the PCV so the PCV cannot draw clean air from the pre-turbo pipe under manifold vacuum conditions. I can stop worry about the restrictor issue then.[/quote]

Preventing flow from the heads to the inlet!
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Re: AOS/CC discussion about air oil separators and catch can

Postby bigBADbenny » Sun Nov 22, 2020 1:27 pm

I have to say my approach is one of analysing the stock PCV system to understand how it works, and then seeing what solutions (if any) are available to improve it.

The major setup was sorting the stock system so no more cracked PCV pipes and leaking injector seats and sensor o-rings: no more phantom knock during cruise, no more oil in inlet.

Whereas you and others have an AOS/CC setup that may add complexity and drag on the stock PCV system and which still doesnt work perfectly or as expected.

I'm trying to close that gap by starting with comprehension of all the varied factors involved.

As regards ultimate wet sump oil control, I'm keen on the ArcTangent Design solution, where the engine was tilted during testing to simulate oil surge in high G corners. Its expensive though! :(
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Re: AOS/CC discussion about air oil separators and catch can

Postby Yowie » Sun Nov 22, 2020 1:48 pm

The simple answer is Provent filtered catch cans, but at what expense to PCV system efficiency?


Is there any info about the actual scrubbing efficiency of these Provents? I suspect the "nothing is 100%" rule will still apply.

As long as air can flow through the catch can I'm not too worried. Note the "small holes" restrictions the factory puts on the crank vent system.

The pic below shows the modified internals to my Mishimoto "long compact" catch can. Air still flows easily (per breath test). See also intercooler and radiator basic principles - lots of metal surface area ('restriction') but the whole assembly is big enough for sufficient flow.

Image

Whereas you and others have an AOS/CC setup that may add complexity and drag on the stock PCV system and which still doesnt work perfectly or as expected.


The only complexity added by my approach is a catch can inserted in each of the factory loops before the engine ingests the dirty air. See comments above on flow.

Re "doesn't work perfectly or as expected", my only complaint is that scrubbing the dirty air is not 100% effective because some funk still gets past each catch can.


Yowie - A lot of those drag & dyno competition cars just vent-to-atmosphere from the catch can on my understanding. Probably better for their application for a lot of reasons including octane preservation under maximum effort runs.

Ben - Yet pulling a crankcase vacuum yields HP gains?


The perfect drag or dyno competition car would probably have mechanical crank gas extraction (to dry sump or otherwise). I suspect many don't and just vent-to-atmosphere for the sake of simplicity and those "low pressure sump" killer wasps are left on the table. "Not knocking at extreme load" is probably the priority, hence no crank gas ingestion by the intake.


Would be interesting to use a PCV as a one-way valve on the cam cover breather return. (Preventing flow from the heads to the inlet)


Then the engine is relying entirely on the crank case vent to exit the dirty air. The balance pipes would need to work harder, perhaps now in one direction only (towards the crank).

Noting the sh!tload of water vapour that gets extracted from my valve covers (on E85) I would be concerned about whether that water can escape as efficiently without condensing within the engine on a longer gas journey to the crank vent.
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Re: AOS/CC discussion about air oil separators and catch can

Postby bigBADbenny » Sun Nov 22, 2020 2:29 pm

But you said you still had some oil in the inlet and intercooler?

I mean that adding hoses adds drag to the system, changing restrictors and pipes around affects the pressure differentials.

We’re not talking absolutes here anyway.

This thread is 100% heuristic in nature.

Its a difficult system to test, other than going worst case cold start e85 torture.
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Re: AOS/CC discussion about air oil separators and catch can

Postby Yowie » Sun Nov 22, 2020 2:48 pm

(1) But you said you still had some oil in the inlet and intercooler?

(2) I mean that adding hoses adds drag to the system, changing restrictors and pipes around affects the pressure differentials.



(1) Correct. I put that down to non-100% scrubbing efficiency of the catch cans and the remarkably large volume of (in descending order) water vapour, aerated oil emulsion and liquid oil coming out of the engine vents on E85.

When I ran on petrol the catch can volumes were much less and different in content blend.

There would be much more cr@p in my intake tract without the catch cans, so what can I do except tolerate it or try to add filtering efficiency?


(2) I've kept the additional hoses as short as possible & avoided mid-hose low points etc. I'm not overly concerned. Some systems advertised seem to run metres of hose to places like battery tie-downs. Such long hoses wouldn't be my choice but the users may comment on the efficacy of the longer-hose setups.

At the end of the day we're not talking mission-critical airflow like past a valve into a chamber. It's just finding a way to get blowby gas out of the engine. Longish hoses of sufficient internal diameter (with no mid-hose low spots) should be fine.

Changing restrictions remains an item of curiosity for me, but most reputable sources seem to say that a higher performance engine means you need larger-than-factory exits for all the extra blow-by gas.

If anyone can post some quality notes on "the value of the deliberate restrictions at different points of the OEM system (and their relevance to a warmed-over factory motor in a street car)" I would be very interested to read it.

Removing my deliberate 6mm restriction from the crank-to-preturbo loop seems to not have changed anything measurable. I removed it to (in theory) allow better crank venting at full load, perhaps at the price of worse crank venting at high vacuum. A worthwhile trade if true.
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Re: AOS/CC discussion about air oil separators and catch can

Postby Kimmo » Mon Nov 23, 2020 4:58 pm

Yowie wrote:Sounds good to me.

Too many acronyms can be confusing though (even though I have said "PCV" a lot like a total hypocrite). If you're doing a round of editing perhaps consider using the long-form of each expression at least once per post.

(Not being a smarty-pants here)

Mad props. Would make this info far more valuable IMO.

PCV systems are totally down in the weeds, extremely nerdy stuff; even as a fairly nerdy nerd myself, my eyes have glazed over several times already from all the unfamiliar TLAs.
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Re: AOS/CC discussion about air oil separators and catch can

Postby bigBADbenny » Tue Nov 24, 2020 4:44 am

Why not pinpoint where you’re uncertain and we can enlighten you. :good:

I’m more interested in joining the PCV system dots at this point and have left the intro post till last, where a more thorough over view will be placed.

There’s other threads on the subject here as well.

Like this one which is very handy:
viewtopic.php?f=18&t=23097&start=60

The important point is that ensuring no PCV system/inlet/intake/crankcase boost vacuum leaks and a not stuck PCV valve is crucial for proper engine running, with correct oil control.

From there, if choosing aftermarket AOS/CC, to correctly route it, with minimal drag on the PCV system.
The latter part seems to be a major hurdle.

Eg my working, tested stock system has no oil in the inlet & tmic, some blow-by residue in the throttlebody hose, thus I have a good basis from which to experiment.

At this point I’m at the same conclusion I reached years ago (linked thread): 2 small cans on opposite sides of the engine for failsafeing oil surge in the heads, one can for the sump breather, pre PCV intake/inlet return.

Basically a poor mans substitute for the KillerB pre AOS anti surge valve.

To really keep blowby out, these would need to be filtered cans eg Provent.
Eg 2x small cans and one medium small.

Although filtered and thus potentially more restrictive, the load is spead across 3 cans, reducing overall drag.
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Re: AOS/CC discussion about air oil separators and catch can

Postby bigBADbenny » Sat Mar 13, 2021 10:19 am

I recently installed a PSR V2 silicone inlet on Ian Wells my07 gtb, 170k km, completely stock.

The car does not use oil excessively, but did have oil in the inlet and throttle body hose.

When I got to look at the car during a recent club lib health check day, the Learning View revealed fuel corrections in the upper range.
The inlet manifold had oil soak evidence at the tgv’s, and the inlet neck at the turbo end was also shiny with oil.

Inlet pressure testing revealed the stock throttle body hose wasn’t even tight at the throttlebody end!
That’ll do it.

We replaced the TB hose, re-crimped the stock tmic end tanks, and the next week did the inlet, mainly because an oil soaked inlet will eventually rot and fail.

On inspecting the old stock inlet, it was very apparent where the oil was coming from, and for me, this was the lightbulb moment, for stock street driven cars, not on e85 and with a stock pcv system.

But even for those other cars, this info may still be relevant.

Think of the stock pcv system, potential oil sources and where we find evidence of oil in the inlet tract.

The stock pcv system has two returns to the inlet pipe: head breathers (larger forward port on the inlet) and the sump breather return (smaller diameter above the compressor inlet)...

So there’s a pressure differential between those two ports that should favour the sump breather over the heads breather.
Both have baffled air/oil seperators too.

But overall the two ports create some equilibrium in the system and this can be seen in crankcase pressure testing a working stock pcv system: pressure hovers within 0.5psi of zero, regardless of load or rpm, its constantly swinging between positive and negative pressure, tending to vacuum under boost.

So the inlet has other returns: fuel purge, boost controller and blow off valve.

The former two cannot be major sources of oil, other than blow-by in the inlet manifold (in the case of the bcs).

But the bov return, that’s going to have blow by in it, but potentially also any oil getting past the turbo journal (or bb cartridge) bearings, as in general, turbo oil drain is reliant on gravity, no restriction in the drain and some crankcase vacuum.

I’d imagine that as the turbo ages, more oil is likely to get past the bearings, regardless, and in doing so may favour the inlet side as this generally under vacuum.

This was evidenced when we inspected the old stock inlet pipe: all the returns were clean, right until the bov return which had clear signs of oil streaming into the inlet back towards the turbo.

So I want to say, if you really want to keep oil from pooling in your inlet, regardless of your catch can/aos setup, I’d consider putting a very high flow, large port diameter aos/cc inline with the bov return, preferably using some type of filter media that can handle the sudden pressure wave.

It should be easy enough to see if this is even a consideration for your car, simply by removing the short fat bit and inserting an inspection camera down the inlet pipe, to see if oil is pooling and if so from which return the oil is entering the inlet.
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Re: AOS/CC discussion about air oil separators and catch can

Postby Yowie » Sat Mar 13, 2021 9:12 pm

So I want to say, if you really want to keep oil from pooling in your inlet, regardless of your catch can/aos setup, I’d consider putting a very high flow, large port diameter aos/cc inline with the bov return, preferably using some type of filter media that can handle the sudden pressure wave.


Very interesting.

Do "vent to atmosphere" blowoff valve users report oil mist sprayed in the area around the BOV trumpet?
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Re: AOS/CC discussion about air oil separators and catch can

Postby bigBADbenny » Sun Mar 14, 2021 10:47 am

The thing that is, we’re talking maybe 20-50mm of pooled oil: max.

And that’s in 170k km.

A little in the well in the stock tb hose, the inlet, and the rest coating the insides of the tmic and inlet manifold.

Something that could probably be kept in check with cleaning every 25-50k km, mainly so as to avoid seepage and contamination of the gaskets and hoses and help with upper engine cleaning.

It would be interesting to install a can on this particular car’s bov return just to see how much it catches.
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Re: AOS/CC discussion about air oil separators and catch can

Postby bigBADbenny » Tue Aug 24, 2021 9:42 am

Its in my latest aos/cc thread.
The info is in the my08 FSM PCV section that refers to the heads breather return as a “fresh air” port.

job_159 2008 Service Manual1.jpg
job_159 2008 Service Manual1.jpg (220.81 KiB) Viewed 3340 times

job_159 2008 Service Manual.pdf
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The arrangement favours vacuum at the sump breather return under boost, when the pcv is closed, pulling air from the heads breather port, into the crankcase and up the sump breather back to the inlet pipe.

The location and diameter of the returns in the inlet pipe create the pressure differential.
Heads breather is large diameter and is further from the impeller (compressor wheel), the sump breather is smaller diameter and close to the impeller for more vacuum and airspeed.

Presumably subaru wanted to achieve a few specifics with this arrangement: crankcase pressure close to atmospheric in all conditions for less bore wiping, and to assist oil return to the sump.

The complexity of the system means intake oil control tends to go haywire (excessive oil in the inlet) when the breather hoses are leaking, because it messes with this pressure differential arrangement.

I recommend watching all the Flatirons YT vids on the Subaru PCV system:
https://www.google.com.au/search?q=flat ... ent=safari

And especially the video where they discuss crankcase pressure testing as part of health checks and verification of a modified pcv system:
https://www.google.com.au/search?q=flat ... ent=safari
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Re: AOS/CC discussion about air oil separators and catch can

Postby bigBADbenny » Tue Aug 24, 2021 7:57 pm

Yowie wrote:But are you saying that different pre-turbo pipes have different ported vacuum that materially affects the stock crank gas breather system?

Apart from some conjecture in the linked catch can thread about which spigots (described by size and proximity to turbo) flow more, I cannot see any evidence in that thread that (eg) Brand X aftermarket pre-turbo pipe affects the stock crank gas breather system differently from a stock pre-turbo pipe or a Brand Y pipe.

[Excluding the "blocking the flow" or "remarkably changing the plumbing" chat of course.]


Flatirons mentioned this in their videos, yes.
The FSM explains the intent embodied in the pcv engineering Subaru debuted with the gen4 turbo.
The solution wasn’t spitballed, it became the default pcv system till today.
That’s why Perrin offered the inlet since year dot, and why most of the aftermarket has finally caught up.
Yes KillerB have the option on their new hard inlet pipe.

Conjecture is possibly related to some comprehensive aos/cc setups still showing oil in the inlet, I’d say.
What would a crankcase pressure test reveal?

If I would hook up a manometer between both ports, yes, we could confirm what subaru already took care of for us :)

Avo style inlets that differ from the stock arrangement:
Its yet another thing grandfathered in from another brand, model, or application.
Like mega heavy aftermarket swaybars and the valving on generic coilovers, you’re going backwards when you have the option to improve.

Ultimately, to get the best out of the stock pcv system or an aos/cc setup, its helpful to first understand the intent behind the configurations for your specific application.
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Re: AOS/CC discussion about air oil separators and catch can

Postby Yowie » Tue Aug 24, 2021 8:24 pm

Flatirons mentioned this in their videos, yes.
The FSM explains the intent embodied in the pcv engineering Subaru debuted with the gen4 turbo.
Yes KillerB have the option on their new hard inlet pipe.

If I would hook up a manometer between both ports, yes, we could confirm what subaru already took care of for us :)

Avo style inlets that differ from the stock arrangement:
Its yet another thing grandfathered in from another brand, model, or application.
Like mega heavy aftermarket swaybars and the valving on generic coilovers, you’re going backwards when you have the option to improve.



Quote above from the first version of your response I found. I see that the edit-after-posting process is relentless so a snapshot record is needed.

1. Please post the specific flatiron video/s and note the specific time/s. I have spent enough time today reading the three-page catch-can thread for a non-existent answer you claimed to be there. As good as it is, I am not going to re-watch the one-hour crank pressure Flatirons video (that I don't recall asserting that different pre-turbo pipes have different ported vacuum that materially affects the stock crank gas breather system).

2. For the third* time, do you claim, based on evidence or conjecture, that different pre-turbo pipes have different ported vacuum that materially affects the stock crank gas breather system?

(*see viewtopic.php?f=18&t=36900 )

3. If "yes, based on evidence" - please supply. Assuming that answering Item 1 does not sort that out of course.

4. If "yes, based on conjecture" - I'm happy to discuss the matter and present my conjecture that any source of ported vacuum in the pre-turbo pipe will be sufficient to do the job (which is just sucking vapours from the crank & valve covers, not critical flow like past a valve.).


Other broad-ranging comments are not of interest to me if we cannot nail down your claimed position on this issue which arises from your original statement:

Using a Perrin or psr v2 silicone inlet (more affordable) should maintain the correct pressure differential in the inlet for the pcv returns, meaning less reliance on an aos/cc setup for a street driven car not running e85.
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