Unmetered air through oil filler?

Daggar

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Jul 19, 2004
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blackcloud50 said:
I see alot of confusion with regards to this particular subject in countless posts and now I am confused somewhat. Here I cut and paste a response that I recieved from one member:

Removing the TB/VC line is not a good idea as this is the source of fresh air for the crankcase. It is the fresh air running through the crankcase that picks up all of the volatile contaminants from the crankcase, to be purged via the pcv.
No TB/VC hose = No Fresh Air = Lots of Contaminants in oil.
The only time this line should be eliminated is if the engine is running boost, or there is a vac pump running on the crankcase.

Using a breather on a pcv system will essentially create a vac leak, as the air entering the crankcase via the breather will not be metered by the MAF. This can cause typical vac leak symptoms.

You may be right about the confusion. In reference to the quote you posted... I don't see what the problem would be having unmetered air enter into the crank case. That portion of the motor is not used for combustion. If that were the case, then you'd not be able to run the motor without the oil filler cap on (which obviously, you can), not to mention the probably THOUSANDS of folks out there that run valve cover breathers on both carb and fuelie applications.

The oil filler neck to throttle body hose is separate from the PCV system. What they have in common is that BOTH vent positive crank case pressures. The PCV from an area that's inhearantly rich in unspent that can also have a tendancy to PULL air during a portion of one engine rotation and PUSH air during another portion of one engine rotation. Thus the requirement for the PCV check valve. The valve cover area (so far as I know) is not effected to the same degree. It's almost a constant PUSH of air form that location, not a PULL or vacuum.
 
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blackcloud50

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Daggar said:
You may be right about the confusion. In reference to the quote you posted... I don't see what the problem would be having unmetered air enter into the crank case. That portion of the motor is not used for combustion. If that were the case, then you'd not be able to run the motor without the oil filler cap on (which obviously, you can), not to mention the probably THOUSANDS of folks out there that run valve cover breathers on both carb and fuelie applications.

The oil filler neck to throttle body hose is separate from the PCV system. What they have in common is that BOTH vent positive crank case pressures. The PCV from an area that's inhearantly rich in unspent that can also have a tendancy to PULL air during a portion of one engine rotation and PUSH air during another portion of one engine rotation. Thus the requirement for the PCV check valve. The valve cover area (so far as I know) is not effected to the same degree. It's almost a constant PUSH of air form that location, not a PULL or vacuum.

Unmetered air that enters into the crankcase will get sucked in by the pcv into the intake causing the a/f to be on lean side. Now I just looked at a good reference manual that reinforces what I have been mentioning above before I said I was confused. Carbed cars will be a little different as there obviously is no MAF.

As stated, the tube that runs from the v/c to the tb is the source of fresh "metered" air that gets pulled into the crankcase and then out via the pcv. (this is along with blowby) This occurs at idle, cruise, and light throttle.

Under heavy acceleration or high speed the crankcase is vented by both the pcv and the tube that runs from vc to tb.
 

Daggar

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How can that be???

The pistons and rings are what separate the induction system from the crank case. The PCV is vented from the TOP of the motor.... The lower intake manifold to be exact. The PCV valve vents going OUT.

Now... take a look at your throttle body where the line comes in from the filler cap. Let me know if you see soot or oil in there. Chances are that you will... even if just a little. What do you think that indicates?

There should be no reason that you would have negative crank case pressure for that line to pull air in unless A) something is wrong or B) I'm missing something and not seeing it (which has been known to happen upon occation... lol) or C) a vacuum pump is being used.
 

criticman

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Sep 7, 2003
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I am 100% with Daggar on this one.

Blow past the top of a straw (90* angle). Air shouldn't reach your fingers. Air is being pulled up through the straw.

Same for the TB. The tube is at such an angle that air is not going to be pulled into it...the positive pressure crossing it (because your engine, a giant air pump, is sucking in air when the TB blade opens) draws air through the tube, into the TB.

As Daggar points out, you will likely find soot/oil where the tube connects to the TB. That is from the crankcase, not magically from behind the TB blade.

The PCV valve lets air out - once again, as Daggar said, it has the check valve (take yours out and play with it). Air can only properly go one way with a functioning PCV valve.

The only air that is supposed to be brought into your engine is through the TB...unless you want to count the smog pump which when setup in stock form, pumps air through one of the tubes into the back of the heads.

EDIT: I too have seen posts similar to what you mention, also talking about how the breather element is "bad" when used to cap the oil fill neck, how it destroys the function of the PCV system, blah blah blah. So, I don't know, maybe I'm crazy, maybe Daggar is wrong...but to me, our view on it makes the most sense.
 

blackcloud50

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Here you can reference-
 

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Daggar

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Nice illustration!!!!

So there is in fact... something I was missing. I had not considered the reduction of the blow by at idle. Illustration B is how I imagined it would run all the time.

It makes sense though. At idle there'd be more likely hood of fuel rich gasses making their way to the crank case. In illustration A, those gasses are scooped up and tossed into the intake.

Illustration B shows the functioning of that system as is normal under power and through the majority of engine operation (if motor is running it stands to reason that you're at power and moving).

Ok... now a question:

I don't think anyone would agree that blocking that oil filler port off is a good idea with out without having seen that diagram. The bad effects are usually pretty apparent within a few miles however....

What then, would be the downside to the air breather that was mentioned before?

At idle, spent crank case gasses would be expelled to the engine bay. So long as you're not in boost (which at idle you'd not be) or there was not excessive amount of oil being put into the filter then it might be ideal. The air entering would be filtered of contaminates prior to being allowed to enter the valve cover.
 

blackcloud50

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Mar 30, 2005
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Essentially the initial poster is allowing unmetered in which many make a too big deal about. His setup is just like having an open breather on the oil fill neck. Both still allow unmetered air into the combustion chamber..to what extent I am unsure.

But regardless of that alot of people use some sort of tuning device and can tune around this if it posed any issue. I believe the that even if the unmetered air was great enough to actually change the a/f, that the feedback from the O2s would make the ECM add more fuel to compensate and return a/f back to what it should be.
 

Daggar

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blackcloud50 said:
If the tube from the vc was routed between the maf and the inlet side of the blower then the system would work just like OEM setup. All air would be metered.

The only problem with that setup might be that if the venturi effect going into the blower is greater than what it is going into the throttle body, then the crank case scavenging that appears in your illustration might not take place.

As for the unmetered air entering into the induction system through the pcv... I'm sure that you are correct in that the adaptive control can easily adjust for such a minute amount of air. Particularly considering (as I mentioned before) the sheer number of individuals running breathers on the valve covers on F.I. cars with zero issues. If anything... I might try installing a restrictor in that line to reduce the amount of incoming air if I'd come across someone showing systems similar to a vac leak with no other apparent issues.
 

blackcloud50

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Daggar said:
The only problem with that setup might be that if the venturi effect going into the blower is greater than what it is going into the throttle body, then the crank case scavenging that appears in your illustration might not take place.

As for the unmetered air entering into the induction system through the pcv... I'm sure that you are correct in that the adaptive control can easily adjust for such a minute amount of air. Particularly considering (as I mentioned before) the sheer number of individuals running breathers on the valve covers on F.I. cars with zero issues. If anything... I might try installing a restrictor in that line to reduce the amount of incoming air if I'd come across someone showing systems similar to a vac leak with no other apparent issues.

I agree that the difference in venturi effect depending on where tube is routed may have some effect as you do mention. But then again, many think (or thought) that the venturi effect at tb in OEM setup was so strong thus not allowing the PCV to pull air from it. And the illustration shows that not to be the case.

Good thing I found that illustration or this could have gone on forever....lol
 

Daggar

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blackcloud50 said:
I agree that the difference in venturi effect depending on where tube is routed may have some effect as you do mention. But then again, many think (or thought) that the venturi effect at tb in OEM setup was so strong thus not allowing the PCV to pull air from it. And the illustration shows that not to be the case.

Good thing I found that illustration or this could have gone on forever....lol

Well it does make sense that the operation of the PCV valve pulse would PULL air from any source it could. Now I'm able to see what it was you were trying to explain at the beginning of the thread. I was not able to envision what it was you were trying to describe.

Now... given that "PCV Pulse" (that's what I'll call it), it does also make sense that for a lack of positive crank case pressure at idle and an otherwise tight system, the it would STILL pull air from that location; having no other as a source.

I still maintain that it's the natural tendency for crank case air to be expelled FROM the oil filler neck port. Only now, I understand why (due the operation characteristics of the PCV) it is that, that's not always the case. Thanks for that! :nice:

My quick summery:

It's expected that crank case scavenging under power is accomplished by the combustion chamber gasses that vent past the piston rings. At idle, it's expected that there will not be enough of those gasses to make that scavenging happen. This is why there's a PCV system... It ensures that crank case scavenging takes place regardless of throttle setting. The better your rings, the more work the PCV will have to do.
 

Nutzy19

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Mar 30, 2005
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Ok I have the same supercharger setup (SN-89) and I
ditched that air filter cover , made my own boostpipe out of 3" black PVC pipe and plumbed a barb fitting in it after the Maf but before the SN's inlet. I ran a 3/8 hose from the oil filler nipple to the barb fitting. Now I have cleaner oil and a better working pcv system. Only downfall is that I have to clean the blower and tb every 10,000 miles to remove oil deposits.
 

Daggar

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I've seen what you're talking about many times Nutzy. A popular fix for that seems to be putting an in-line fuel filter between the line and the throttle body. Give it a shot and see if it works for ya.

Just need one of those see through deals in the help section of the parts store.
 

blackcloud50

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Nutzy19 said:
Ok I have the same supercharger setup (SN-89) and I
ditched that air filter cover , made my own boostpipe out of 3" black PVC pipe and plumbed a barb fitting in it after the Maf but before the SN's inlet. I ran a 3/8 hose from the oil filler nipple to the barb fitting. Now I have cleaner oil and a better working pcv system. Only downfall is that I have to clean the blower and tb every 10,000 miles to remove oil deposits.

You should put a separator or filter inline between the tube running from nipple on filler neck and the inlet side of blower. Vortech kits come supplied with a filter.
 

Strype

Cuthbert catcher
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May 11, 1999
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:D Okay subscribing...

So if I can ask ya real quick guys, I have a blank TB spacer, no egr, no smog pump. Will it hurt my N/A stock car to cap off at the TB and have that little filter on the Oil Filler Neck??? Seems to run fine :shrug:
 

blackcloud50

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HoodStrype said:
:D Okay subscribing...

So if I can ask ya real quick guys, I have a blank TB spacer, no egr, no smog pump. Will it hurt my N/A stock car to cap off at the TB and have that little filter on the Oil Filler Neck??? Seems to run fine :shrug:

It will be fine
 

JChalfan

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Nov 27, 2002
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Daggar, blackcloud and others: Thanks for all the posts, they were incredibly informative. Especially the diagram. I have seen a lot of confusion about this issue in other threads I have read. This has definitely helped clear it up.

So it sounds like in some situations (at idle mostly), I do in fact have a small amount of unmetered air entering the engine. Whether or not it's enough to effect the engine seems to still be undecided, but it does make sense that the computer might be able to adjust for it using the O2's.

Once I get some sort of hard intake pipe for my SC (not my dryer tube setup), it sounds like the best thing would be to install a fitting and route the line from the oil filler into my SC intake (after the MAF), with a oil seperator.

Nutzy, I'm curious what your home made boostpipe looks like, I'll send you a PM.

Thanks for all the info, this thread has probably helped a lot of people.

Jeff