Unmetered air through oil filler?

JChalfan

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Nov 27, 2002
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I have a '90 5.0 with a Paxton supercharger. When I installed the kit, I removed the hose from the oil filler to the throttle body. I plugged the throttle body where the hose went, and my supercharger kit came with a hose that goes onto the oil filler and runs into the air filter cover.

I searched on this topic quite a bit, and everyone said to just leave the stock oil filler to TB hose in place on a naturally aspirated car. Unfortunately I can't do that, or I will pressurize my crankcase under boost. I couldn't find much information on what to do with a supercharger

I realize I am letting unmetered air into the engine, and that's not a good thing. My PCV system is completely stock.

Does anyone have any suggestions?

I saw a post where someone else ran the line from the oil filler into a threaded fitting in their SC intake tube, after the MAF. I don't have a hard pipe going into the SC though, so I don't see how I could do that.

Here's a picture in case my description sucked.

oilfillerline.jpg


Thanks a lot.

Jeff
 

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Daggar

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Jul 19, 2004
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You are NOT allowing unmetered air into the engine with that configuration.... not unless there is a SERIOUSE internal engine problem.

The pistons and rings are intended to separate the top of the engine and combustion chambers from the bottom portion of the engine. Ideally, there would zero exchange of gasses between those two areas. Now we all know that there is a certain amount of combustion chamber gasses that are acceptable for making their way past the rings and into the crank case without causing problems. The setup that you've got going in the pic takes those vented crank case gasses and routes them back through the intake system. I would be the same if you vented the oil filler neck directly to the throttle body.

I do not see any cause for concern in the setup depicted in your post or picture.
 

blackcloud50

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Mar 30, 2005
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Daggar said:
You are NOT allowing unmetered air into the engine with that configuration.... not unless there is a SERIOUSE internal engine problem.

The setup that you've got going in the pic takes those vented crank case gasses and routes them back through the intake system. I would be the same if you vented the oil filler neck directly to the throttle body.

I do not see any cause for concern in the setup depicted in your post or picture.

First I would say that I've seen numerous posts concerned with letting unmetered air into the engine when using an open breather and PCV set up. I believe people make too big of a deal with regards to it.

Second, the setup pictured, which is the same for Vortech install, essentially allows unmetered air into the combustion chamber because of the postion of the hose routed from nipple on the oil fill neck in relation to MAF. It needs to be after the MAF, not before.
 

Daggar

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The thing is: If it's crank case air then it's already been metered. It slipped past the rings in order to get to the crank case inthe first place. So essentially, it's allready been metered in order to make to the top of the pistons.

Excessive blow-by might cause a problem but if that's the case, there are more serious issues at hand beyond worrying if air is bypassing the MAF.
 

TheRedBlur

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Jul 7, 2003
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like everyone said, if it's between the MAF and the throttle body, you're good to go, it's already been metered. The tube is there because when vapor gets sucked through the PCV, it's unmetered, so the filler neck to intake tubing makes up for that. Believe it or not, air travels from the intake tube TO the valve cover, not the other way around, unless you are under heavy acceleration in which case the amount of air drawn in pales in comparison to the WOT draw from your engine. there was a long and sort of confusing thread on PCV about a week ago.
 

criticman

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Sep 7, 2003
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And when it is connected to the air filter cover (I have this setup too, Novi 1000), it is not really doing all that much to pull that air out and into the filter to the MAF, etc. It is just producing some positive pressure across it, as it does when the tube is connected to the TB. It pulls it up to help "relieve" the system.
 

JChalfan

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Nov 27, 2002
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Daggar, congrats on becoming a moderator!

Looking at the picture I already posted, it may be a bit misleading. It looks like the line from the oil filler is being routed back into the intake system after the MAF, but in fact it's not. The hose from the filler just "dumps" into the air filter housing, so it is essentially open like I was running an open breather. Here is a pic of the air filter cover flipped over, you can see the hose doesn't connect to anything:

View attachment 462566

With the engine running, if I pull the hose off the oil filler and cover it with my finger for a couple seconds, when I take my finger off I can hear a small amount of air being sucked into the valve cover from the vacuum that built up.

Thanks for all the responses.

Jeff
 

Daggar

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Jul 19, 2004
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Ok.. so basically what you're saying is that your crank case air is being re-metered as it goes into the motor.

Even so, I still don't see this as being a problem. Here's why.

The metered air that goes into your intake is measured by the computer. The computer then adjusts the injector pulse width to provide what it thinks the ideal air/fuel ratio is. If you do have any blow-by, then it is from gasses that are already "spent" from combustion. Therefore, that air has already been mixed with appropriate level of fuel to go "bang" and push the piston down. Routing those spent crank case gasses back to the inlet (whether it's prior to or after the meter) is more of an emmisions thing than anything else. It's an attempt to have the motor burnt any remaining unspent gasses. The mass of air that's able to travel through that relatively small hose might make for a nice vac leak if improperly routed to the intake but otherwise will be inconsequential.

If you're feeling vac to the valve covers at idle but that tube has positive pressure when you're in boost then that tells me that things appear to be in good order. Plugging that line is not a good idea (if you considering that). You would prevent excess case pressure from leaving and probably end up forcing it through the PCV system.

If it's bother you or causing a problem then you might consider deleting that line all together and installing a valve cover breather. I don't recall you indicating that it was causeing a problem though. I'd leave it just like it is. It's standard configuration for a lot of blower setups.

The big thing is just that you don't want that line fed to the throttle body or intake when you're under boost if there is any significant amount blow-by due to the additional boost pressure.

Does that make sense?
 

Daggar

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Jul 19, 2004
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On a side note:

Were it me, I'd get a Power Pipe to replace that dryer hose you got there. If nothing else, it should reduce your blower outlet temps a degree or two and provide a little more air mass to the blower inlet.
 

blackcloud50

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Mar 30, 2005
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Daggar said:
Ok.. so basically what you're saying is that your crank case air is being re-metered as it goes into the motor.

Even so, I still don't see this as being a problem. Here's why.

No.
Since he has the stock pcv valve set up and installation as in his picture, he is pulling in unmetered air into the combustion chamber. In my opinion the amount being introduced into the combustion chamber this way is so small that it shouldn't create any concern.

Crankcase air being re-metered is of no concern here.
 

JChalfan

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Nov 27, 2002
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Daggar, makes sense, thanks.

As far as I know, it's not causing a problem. I have a part throttle pinging issue, which I have solved by setting the timing at 6 or 7 degrees BTDC with the spout out. The car pulls strong with the timing where it is, and I'm beginning to think my balancer may have slipped a bit or something, and my timing isn't really as retarted as the timing marks indicate.

I was thinking that this unmetered air might be contributing to the part throttle pinging (low rpm's, unrelated to supercharger). I doubt it is. I may try plugging the line from the oil filler just to test the theory, but I have no intentions of plugging it for the long term.

I have thought about a powerpipe. I'm not sure they make one specifically for my old school Paxton SN92. It's more a matter of $$$ at the moment, I just bought a bunch of suspension stuff for my car. I should start looking into it more though, I don't like the dryer hose.

Thanks for the help.

Jeff
 

blackcloud50

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Mar 30, 2005
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What you guys seem to be missing is that in the stock, OEM configuration, the tube that normally runs to the TB from the valve cover is where the PCV pulls "metered" air from to flow into the crankcase and out the PCV valve to the upper intake.
 

TheRedBlur

Active Member
Jul 7, 2003
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if it aint broke, don't fix it lol. its a good thing to have that tube there, it lets fresh air in, which in turn slows oil deterioration. It's not like the motor is gonna blow up or anything. if you had a loud tick, then that'd be different.
 

Strype

Cuthbert catcher
Founding Member
May 11, 1999
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I have a small red filter on my valve cover... go to advance auto parts and pick one up- it looks a lot better than the hose :D

PS: Believe it or not it's made by APC and fits perfectly
 

Daggar

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Jul 19, 2004
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blackcloud50 said:
No.
Since he has the stock pcv valve set up and installation as in his picture, he is pulling in unmetered air into the combustion chamber. In my opinion the amount being introduced into the combustion chamber this way is so small that it shouldn't create any concern.

Crankcase air being re-metered is of no concern here.

I'm not sure what you mean here. The PCV system (Positive Crankcase Ventilation Valve) is not depicted in either of the images above nor does it introduce unmetered air into the combustion chamber. All it does is vent positive crank case pressures to the intake. If there IS positive pressure in the crank then it's already been metered.

I'm think that I'm just not understanding what you're saying here.
 

blackcloud50

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Daggar said:
I'm not sure what you mean here. The PCV system (Positive Crankcase Ventilation Valve) is not depicted in either of the images above nor does it introduce unmetered air into the combustion chamber. All it does is vent positive crank case pressures to the intake. If there IS positive pressure in the crank then it's already been metered.

I'm think that I'm just not understanding what you're saying here.

The pcv system is not depicted in the photo but the original poster says that "my pcv system is completely stock". SO.....

The tube that used to run to the tb from the v/c (where it allowed "metered" air to flow into the crankcase" is no longer there). Rather it is routed before the MAF where it is now pulling in "unmetered" air from the atmosphere into the crankcase.

Does this explanation help?
 

go4it

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Jul 15, 1999
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blackcloud50 said:
The pcv system is not depicted in the photo but the original poster says that "my pcv system is completely stock". SO.....

The tube that used to run to the tb from the v/c (where it allowed "metered" air to flow into the crankcase" is no longer there). Rather it is routed before the MAF where it is now pulling in "unmetered" air from the atmosphere into the crankcase.

Does this explanation help?

The hose that ran from the v/c to the throttle body, wouldn't the air be sucked into the throttle body from the v/c? Now the hose is ran in front of the mass air to the filter box where it will also have air sucked from the v/c. It is doing the same thing in either location, it just can't be after the supercharger now because it would pressureize the crankcase. Thats the way that I see it,
 

Daggar

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go4it -- you got it bro. :nice:

As for the oil filler vent "sucking air in". That's not likely to happen unless there is a problem. The crank case vent on the valve cover will release positive crank case air, not suck it in. Leaving that port completely open doesn't create a vacuum. Instead, you'd stand a much better chance of oil dropplets being expelled.
That positive air again, comes from gasses expended in the combustion chamber that slips past the rings and down into the crank case.

Too much of this "blow by" can create a problem. Some small amount of course, it acceptable and expected.

Many racers run vacuum pumps to the crank case to ENSURE a negative air pressure in that area. It helps to seat the rings, and reduce the amount of blow-by present in the crank case.

I think you may have the airflow coming from that oil filler neck backwards. On an OEM setup, crank case air flow INTO the throttle body. Not the other way around.
 

blackcloud50

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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.