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Crank Case breather question

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Old 10-16-2007, 08:07 PM   #1
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Crank Case breather question

Hi Guys,

what is the purpose of a crank case breather? Ive heard a few guys talk about it and i have no idea what this would be? What are the advantages of it?

Thanks,
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Old 10-17-2007, 12:22 AM   #2
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In any engine, you need to vent the crankcase (the part below the pistons) because you will get some blowby of combustion gases past the pistons. In the pre-emission days, this was accomplished by venting the crankcase to the atmosphere through a crankcase breather or filter. When people became concerned with emissions, the PCV (positive crankcase ventilation) system was used to pull the blowby back into the intake manifold and burn it in the combustion chamber instead of letting it vent to the atmosphere.

The only benefit of using a breather that I can think of is that the carbon deposits that form around the throttle body and intake manifold are mostly the result of the PCV system. So perhaps the upper intake would stay cleaner with a crankcase breather. However, I don't believe that it is legal to modify or remove the PCV system under Federal Law because it is part of the emission system.

I don't see a performance benefit unless there is something I'm missing.
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Old 10-17-2007, 07:28 AM   #3
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well-put, Dogfriend! That pretty much sums it up!

If you were to install a breather cap in place of the oil cap, the odds are your vehicle would notice a lean condition due to the PCV system drawing in un-metered 'fresh' air through the crankcase. There is no performance benefit to using one.

-Joe




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Old 10-17-2007, 08:01 AM   #4
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If you were to install a breather cap in place of the oil cap, the odds are your vehicle would notice a lean condition due to the PCV system drawing in un-metered 'fresh' air through the crankcase. There is no performance benefit to using one.

-Joe
I have had a breather on mine for quite some time. I do not experience any lean condition. I have experienced no ill effects whatsoever.

The major plus is that the throttle body stays clean since the install of the breather.




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Old 10-17-2007, 08:13 AM   #5
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I know, Al, I know. We've had this discussion before.

I should have stated that in some cases, it can cause a lean condition. There's no denying the fact that it lets un-metered and (depending on the breather one uses) un-filtered air into the intake air stream.

In *some* vehicles, it doesn't matter, however. The breather element on my old Dodge Caraven was in the air filter housing, so the air recycled back into the intake was up-stream of both the air filter and the Mass Air Flow Sensor. That's not always the case.




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Old 10-17-2007, 09:28 AM   #6
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I'm assuming that if you add a crankcase breather, you remove the PCV valve and plug the port in the intake manifold. Otherwise you would have a huge vacuum leak.

In California, you would have to switch back at smog test time because it would fail the visual part of the smog test without a PCV system.
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Old 10-17-2007, 09:40 AM   #7
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I too have the crankcase breather, and no ill effects either. It does keep my intake much cleaner and the oil seemed to last a little longer, wouldnt get so dirty so quickly.
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Old 10-17-2007, 09:42 AM   #8
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I'm assuming that if you add a crankcase breather, you remove the PCV valve and plug the port in the intake manifold. Otherwise you would have a huge vacuum leak.
Nope, the PCV valve is left intact. There is no vacuum leak.




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Old 10-17-2007, 09:47 AM   #9
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Nope, the PCV valve is left intact. There is no vacuum leak.
Are you using a breather that replaces the oil cap? I was thinking that it was a breather that would install in place of the PCV line coming out of the crankcase.
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Old 10-17-2007, 10:24 AM   #10
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Are you using a breather that replaces the oil cap? I was thinking that it was a breather that would install in place of the PCV line coming out of the crankcase.
No. The breather replaces the hard plastic line from the passenger side valve cover that goes to the intake tube.




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Old 10-17-2007, 11:55 AM   #11
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No. The breather replaces the hard plastic line from the passenger side valve cover that goes to the intake tube.
What happens at the other end of the line? Do you plug the port? Maybe a picture or link?
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Old 10-17-2007, 12:03 PM   #12
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Yea, you plug it, ill, go to this link, sorry the pix is small, but it does the job, hope this helps.



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Old 10-17-2007, 01:56 PM   #13
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I will have to look at the diagrams to see the routing of the PCV system, but I'm pretty sure that the PCV valve is just dead weight because the breather will break the vacuum in that circuit. I'm still not sure why it wouldn't be pulling unmetered air (aka a vacuum leak).....
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Old 10-17-2007, 05:53 PM   #14
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Because that doesnt have to do with ANYTHING with the pcv system at all. It filters the gases from the crankcase over the valve cover. i dont know alot about PVC systems, but i know this doesnt effect it at all. And the filter isnt puling in air, its releasing it. and instead of putting it through the intake again and getting oil in your manifold, it just releases the gas into the atmosphere! (sp?)
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Old 10-17-2007, 06:26 PM   #15
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Thanks for all of the info guys. So, the main point is to keep the intake cleaner. But, i was wondering, does this help at all with keeping the air being taken in colder? I dont how big of difference it will make, just an idea. I imagine that this mod plus plugging the erg valve would make some difference? Does anyone have this done also?
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Old 10-17-2007, 06:26 PM   #16
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instead of putting it through the intake again and getting oil in your manifold, it just releases the gas into the atmosphere! (sp?)
That is what the PCV (positive crankcase ventilation) system was designed to prevent. Instead of releasing the gas into the atmosphere (where it contributes to the emission problem aka pollution) it recirculates the gases into the manifold.

I have no doubt that the breather works since engines were built this way back in the 50's and 60's, but those engines were carburated, not fuel injected, so there was no feedback to try to control A/F ratios.

I will look at the diagrams when I get home later this evening and try to figure out what is happening to the rest of the PCV flow when you substitute the breather for the tube going to the intake.

Right now, I agree with GI Joe, I think you are pulling unmetered air through the breather, but I haven't looked at the details of how the flow is routed for the SOHC engine.

Does the breather have a check valve? (i.e. Can air flow both directions through the breather, or just one way?)
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Old 10-17-2007, 06:57 PM   #17
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Does the breather have a check valve? (i.e. Can air flow both directions through the breather, or just one way?)
No check valve.

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Old 10-17-2007, 06:58 PM   #18
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I imagine that this mod plus plugging the erg valve would make some difference? Does anyone have this done also?
Eliminating the EGR valve is not a good idea.




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Old 10-17-2007, 07:11 PM   #19
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Ok, Ok,

If I were to disconnect the Oil fill breather from the intake, should I plug it, install a filter, or install a one way valve?

If I install a valve, should it allow air in (back through the PCV valve) of should it vent out (Back into the atmosphere)?





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Old 10-17-2007, 07:35 PM   #20
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If I were to disconnect the Oil fill breather from the intake, should I plug it, install a filter, or install a one way valve?

Yes, you must plug the opening in the intake tube.




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