Re: AOS improvement

There is a great write up by Pedro on replacing the AOS
[www.pedrosgarage.com]
There has been a lot of discussion about improving the effectiveness and longevity of the AOS. I don't consider the $1000 "motorsports' part aserious option.
One of the affordable enhancements sometimes mentioned is fitting a catch can between the AOS and the inlet manifold. But there is no definitive "This is the Answer" diy proposal that I could find .
The catch can addition may help after the diaphragm has started to fail but you would have to be OCD to check the can frequently enough to observe a sudden increase in aqumulated oil?
A catch can may also provide an effective secondary 'scrubber' to remove oil in the fumes that escape the AOS even when it is in good working order ?
What I am striving to achieve is an oil-free intake system. I have recently cleaned the inside of the entire intake system and it was filthy will oil deposits. I presume that some of the oil was just a result of a less than 100% effective AOS?
Has anyone got any experience of an effective oil catch can on the M96?
I have found them to be very effective on other cars but space is so limited on the Boxster ,I am reluctant to start experimenting.
Thanks for any suggestions.

have an oil free intake unless you fit some lab quality air/oil separator between the AOS and the intake system, and a catch can ain't it.

The bit of oil that ends up in the intake and eventually gets burned by the engine is of no consequence. My advice would be to follow good oil hygiene practices and move on.

Actually it does not get burned -it lines the intake manifold and causes well known problems in any engine.
Striving to make improvements despite the difficulty seems to be the essence of owning a Porsche .
And a great man said:"Expect the best, and accept no substitute". I like that approcah to Porsche upgrades.

Quote
tonyd
Actually it does not get burned -it lines the intake manifold and causes well known problems in any engine.
Striving to make improvements despite the difficulty seems to be the essence of owning a Porsche .
And a great man said:"Expect the best, and accept no substitute". I like that approcah to Porsche upgrades.

and the matter, it does get burned. And I have read of no post, have heard of no report of any Porsche engine intake suffering from this condition.

The oil won't hang around but gets pulled into the engine and burned. There are no well known or even any not so well known problems with this seemingly neanderthal method disposing of crankcase fumes (and any oil vapor that gets carried along with the fume's other ingredients) or the streets would be clogged with broken down cars. Every automaker uses for all practical purposes essentially the same method of crankcase fume disposal for its automobiles.

Uh, check that: I kind of take back that no well known problems comment in at least one case. During my time with my 2002 VW Golf TDi I learned that the engine could suffer from an intake blockage due to a build up of a mixture of soot (courtesy of exhaust gas recirculation intended to pollute the incoming air and lower combustion chamber temperatures to avoid the creation of NoX) and oil vapor (courtesy of the crankcase ventilation system failing to remove all the oil vapor from the crankcase fumes) that over time would harden and form into what many VW TDI owners referred to as "coke" that would line the intake walls to the point the flow of air into the engine would be insufficient for any engine speed above a fast idle.

Rather than fret about this like many other owners did I relied upon fundamental good engine hygiene which included regular oil/filter services (every 5K) and running a good oil -- Mobil 1 0w-40 (IIRC recommended by VW) -- along with using good quality diesel fuel and avoiding operating the engine at too low an RPM kept the intake free of any buildup. Shortly before I sold the car with IIRC around 140K miles on it I checked the intake and while the inside walls were coated with a black oil film the film showed no signs of any build up.

'course, you are not alone in your "concern" regarding finding oil in the intake manifold. The Challeger R/T forums are full of posts bemoaning the presence of a bit of oil in the intake. One might have thought the owners found feathers for all the clamor that is being made and all the wild schemes being put forth -- including catch cans -- to deal with it rather than just let it be as it does no harm.

While I admit I didn't know Dr. Porsche I dare say you are no Dr. Porsche. But I will withhold judgement on any modification you make in this area regarding whether or not it is an improvement until after there has been some time passed and the benefit (or lack there of) of your modifications is better known. 'course, by what metrics we shall know this I have no idea. The Dodge R/T boys go all crazy with joy over finding a teaspoon of oil in the bottom of a catch can after thousands of miles of driving. That many more teaspoons of oil were not caught doesn't cross their minds. Periodic disassembly to inspect the intake walls to monitor the effectiveness of the catch can setup is not practical.

until the AoS truly fails and large amounts begin to move into the intake, why is this such a problem?

My intakes were fairly clean - no, not spotless,bit better than most cars i see that rely on PCV valves and a rubber hose...

Since i've had two AoS failures, i too, would like something better. but i am not aware of issues before they fail (e.g.: during normal operation, up to the point of failure). Also, both of my failures occurred during or immediately after extended track use, and during very hot weather. Conclusion: the membrane melted.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

Quote
grant
until the AoS truly fails and large amounts begin to move into the intake, why is this such a problem?

My intakes were fairly clean - no, not spotless,bit better than most cars i see that rely on PCV valves and a rubber hose...

Since i've had two AoS failures, i too, would like something better. but i am not aware of issues before they fail (e.g.: during normal operation, up to the point of failure). Also, both of my failures occurred during or immediately after extended track use, and during very hot weather. Conclusion: the membrane melted.

Grant

My Boxster has gone through 3 AOS's now. Each was fine until rather suddenly it wasn't. The bit of extra oil passed through to the engine in the latter failing stages of the AOS would have overwhelmed a catch can of any reasonable capacity.

(As an aside, I too would prefer a more durable AOS, but it ain't going to happen. Oh, I don't consider the Motorsport AOS a viable alternative given its very high cost and in more general terms that it is not 100% with but a subset of the cars.)

I see no benefit in going to the trouble of fitting a catch can for what in the case of my Boxster occurs once every 80K to 100K miles and for which the catch can would be of no value.

The 1st AOS failure I went overboard and had the plugs replaced and asked the intake be cleaned out. I doubt the intake was cleaned out, as I do not recall seeing any labor time listed for this.

The 2nd and 3rd times I didn't bother. I just drove the car and any oil in the engine worked its way out and did so with no issues. Plugs didn't foul. Engine didn't misfire. The engine didn't even smoke any after a bit of smoke upon the 1st start after I got the car back.

Oh, I doubt the AOS membrane melted. No other seals -- internal or external -- suffer any signs of melting and they are all exposed to the same hot oil. What I suspect happens is tracking subjects the membrane to excessive flexing. This is the failure mode I observed when I cut a bad AOS apart. During track time the extremely high RPMs coupled with closed throttle coast down from high RPMs means the intake pressure swings from nearly atmospheric pressure to very low pressure and back again over and over as the engine RPM's rise and fall. Since the AOS membrane is exposed to this extreme pressure difference this just accelerates the membrane's failure mode.

The membrane is like I guess in some ways a plastic fork. One can slowly and only slightly bend the fork handle back and forth and over time the handle will fail at the bend. But if one vigorously bends the handle and bends it more of course the handle fails sooner.

I did see a write up where someone used Moroso catch can and hoses to replace the AOS. Had it mounted in the trunk.
I think it was from Texas. Silver Boxster if I remember.
I would think there is a work around for the AOS.

No I am not an Engineer and I did not stay at Holiday Inn last night.

Quote
Van914
I did see a write up where someone used Moroso catch can and hoses to replace the AOS. Had it mounted in the trunk.
I think it was from Texas. Silver Boxster if I remember.
I would think there is a work around for the AOS.

No I am not an Engineer and I did not stay at Holiday Inn last night.

against an intake backfire and the overpressure blowing out expensive to replace seals. It also serves to quench any flame from a backfire to avoid igniting explosive fumes in the crankcase. A catch can might quench the flame but it won't deal with the overpressure.

A catch can mounted in the trunk is not a viable solution to me. I want the Boxster's rear trunk left alone as a major factor for buying the Boxster was its impressive amount of trunk space. A catch can in the trunk not only eats into valuable space but puts the catch can plumbing at risk of being damaged using the trunk for well, carrying stuff.

Might add that a catch can mounted in the trunk requires holes be cut on the car's sheet metal to run the vapor hose to and then from the catch can just puts one more nail in a catch can's coffin.

In the case of a Boxster (or really any Porsche model made in oh the last 50 years or so that came with a factory installed crankcase ventilation system) a catch can is a solution for a problem that doesn't exist.

The membrane is suspended by a 'surround" much like a speaker cone the surround allows it to move back ad forth, as you describe.

In both of my actual failures, the surround cracked (just like speakers often do!). It may be due to the rapid flexing, as you propose, or due to weakening with hot oil, as i do, or both.

I really don't know, your explanation is just as plausible - maybe more so.

Interestingly, i also had two other AoS "failures" but it was not the membrane at all - it was the bellows that secures it to the crankcase (the breathing point). I have no idea why. few others see this, but i had two.

in fact, you all may recall that last year i was using more and more oil and suspected motor issues. It appears that it was different, a strange combination of three minor issues:

1. the techno sump gave me inconsistent, erroneous low readings, which caused me to inadvertently over-fill
2. The bellows broke ( maybe due to #1?)
3. A spark plug tube cracked

While my car uses oil, it now uses a very reasonable amount, and passed both leak-down and compression testing with decent - good readings.

Grant

Grant

gee-lenahan-at-gee-mail-dot-com

believed that in a good number of cases where an engine uses a lot of oil and with no real signs the oil consumption arises from the more common sources of excessive oil consumption: bad rings/piston/cylinders or bad valve guides/seals; the excessive/elevated oil consumption is not due to the engine but due to the AOS.

The AOS's oil vapor removal performance is subpar due to just a lousy design/implementation or as your post strongly suggests because of some non-catastrophic failure with the failure's only real symptom (my theory at any rate) is more oil consumption because the failure has reduced the AOS's efficiency.

A problem is that I am not going to advise someone with a car with an "oil consumption problem" to replace the AOS unless the AOS clearly needs replacing due to an obvious failure or problem with the AOS. A suspicion of it contributing to excessive oil consumption is not sufficient.

OTOH, I have to say that were it my car I'd seriously consider doing this but would talk things over with a tech to see if there was some way to qualify the performance of the AOS to perhaps ID the AOS was under-performing. I might even push to have this put to the factory to see if the factory could suggest some test/measurement.

I thought of one way though I hesitate to mention it given the context of this thread, but what the heck, and that is to install a mini-oil catch can in the hose between the AOS and the intake manifold to get a handle on the amount of oil the AOS is passing through to the intake. If the amount of oil in the catch can over a span of say 250 miles of normal driving was excessive - what excessive would be I am not sure, but on the order of ounces, then this could suggest the AOS was the reason the engine was using oil.

Possibly then I could ok an AOS replacement and retest the AOS with hopefully finding less oil in the catch can over the same number of miles and the same usage as before.

and i really am! :-)

Grant

gee-lenahan-at-gee-mail-dot-com

If you start monkeying around with the intake, it might also affect the computers. I would think the intake computations take into account the added pressure, hydrocarbons, etc that the crankcase would went into the intake.

I have seen setups on older cars where the crankcase is instead vented to atmosphere with a catch can to prevent signigicant oil loss. But those setups were all pre-OBD II. I bet that the Porsche engine management takes this vented air into account and changing the configuration could result in a rich/lean problem.

In short, I submit that changing one parameter may well require changing others - kind of like a pandora's box. Bottom line, I would not want to be the guinea pig - but if others have already done....

Do long and broad research...

Jm ,thanks for your concern.Monkeying ? I'm Mech Eng.You?
The DME will function much better without 'reading' corrupted data caused by the oil contamination in the Intake. Detonation is the eventual consequence because the DME will retard the spark excessively to compensate for the oily mixture.The presence of the oil depresses the effective RON/octane.This is a common problem in forced induction also.
The fumes are not vented any way other than the Dr. intended. We are just removing excess oil that occurs when the AOS begins to fail.Smog Test results would improve especially for HC.
The risk of carbon build up in a nice newly rebuilt engine is unacceptable.
For the Boxster,the catch can is best fitted in the trunk ,so it is easy to check.
The main challenge is the fittings. The lines are very large diameter - approx. 1-1/4" so standard catch cans are useless. Probably need (?) -20AN 90 degree bulkhead AN833-20 (mocal). Need a totally sealed system if it is in the trunk! Any suggestions about fittings?
I speculate that this catch can mod. is ideal when combined with Pedro's Deep Sump and horizontal baffle. Why? - because some of the AOS failures seem to be associated with over-filling the sump and Track use. With a deep sump+baffle(correctly located!) there is no need to worry about running with an oil level between "Min" and 1/2 full. The pickup has an extra 2 qts of oil to 'feed' from and is submerged at all times(including Track & turn 17 at Sebring). So I am hoping Pedro will chime in and tell us what he has done- if anything.
It may be that simply running the oil level between Min. & 1/2 full in the Deep Sump is all we need to minimize intake oil contamination? If so ,that is another reason to install Pedro's Deep Sump kit.I did.



Edited 1 time(s). Last edit at 03/06/2015 04:40PM by tonyd. (view changes)

To answer your immediate question, I have been on this board and its predecessor for a number of years. I have been a lurker on several other boards. I have never seen - or at least I do not recall - a detailed post about creating a catch can/vented to atmosphere bypass on a Boxster engine.

That is in marked contrast to other boards I float around. Because it is such a common hack with other marques, I would think that someone must have tried it on a Boxster at some point in the history of man. That said, if folks have not heard about it, that - itself - should tell you something.

Given your question, I assume you are trying to do something new and different. That is cool by me. You will note that I did not critique the plan by suggesting it was not smog compliant or whatever. That said, if it were my car I would be worried about confusing the computer brain. If you have that potential problem thought out or worked around - good. As an engineer, I hope that your proposed solution works as intended.

But I could hardly be expected to know that you are an engineer. Or anything else about you for that matter. In answer to your second question - I am not an engineer nor do I play one on TV.

I NEVER said vented to atmosphere !!!!!!!!! You did.

In my Boxster there is over a foot of distance between the MAF and the AOS connection to the intake. The MAF doesn't get fouled with oil from the AOS. I have driven my Boxster over 100,000 miles and not bothered to clean the MAF.

While oil in the intake charge can affect gasoline's octane rating, it lowers it, I'm not sure by how much. I suspect way less than the difference between 93 octane vs. 91.

Also, the amount of oil an otherwise healthy AOS routes to the engine is minuscule compared to the amount of oil that it put into gasoline at the refinery.

My info is gasoline contains 1% oil added to help prevent steel lines and pipes and tanks that carry or are exposed to or used to store the gasoline from rusting.

My Boxster engine uses 1 quart of oil in 5000 miles. In that same 5000 miles the Boxster engine burns 200 gallons of gasoline, assuming 25mpg fuel consumption. This 200 gallons of gasoline contains 1% oil which works out 2 gallons of oil. Another quart of oil on top of this is of no consequence.

Also, I have to point out that the way the AOS works under hard acceleration or under low throttle opening but high engine load when any degradation of the gasoline's octane rating could have an affect on the amount of timing advance the DME could dial in the AOS is less active as the intake pressure under these conditions is higher than it would be at other times. When the air pressure in the intake manifold rises the amount crankcase fumes drawn through the AOS falls way down and thus less fumes routed to the intake the less oil vapor routed to the intake manifold and in this case essentially the intake charge is not contaminated to any substantial level by any oil from the AOS.

One has to consider what impact a catch can plumbed in to the existing crankcase ventilation system would have on the effectiveness of the crankcase ventilation system. The extra lines, sharp bends, the general restriction to air flow introduced by the presence of a catch can means the speed of air flowing through the AOS would likely be less thus the effectiveness of the AOS is reduced. The catch can could look like it is it really "catching" the oil but it is doing this because there is more oil to catch due to the negative impact catch can has on the effectiveness of the AOS.

oh my. another "engineer"... seriously, unless you work in the auto business designing cars and specifically car engines, you are just tinkering. Dont be offended if someone says youre "monkeying around"

Actually ,that is exactly what I did.
But I can see I chose the wrong Forum.

is the (unnamed) well-know non-engineer Porsche engine rebuilder who claims that everything of his is over-engineered.

marketed instead?

"A mile of highway will take you one mile. A mile of runway will take you anywhere."

Yes