Breather=Unmetered Air !!??
11-23-2006, 05:55 PM
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Breather=Unmetered Air !!?? In an effort to keep oil out of the intake manifold/combustion chamber.....
Many of us run a catch can in the PCV line (valley to intake manifold line). Then instead of running the passenger valve cover line to the TB (or air bridge on LS2) we put a breather in place. Or cap the vent and put in a breather oil cap.
There seems to be two schools of thoughts.
1. That this is a good idea which allows venting of crank case.
2. That this is a bad idea because it allows unmetered air (not seen by the MAF) to enter the engine .... specifically the intake manifold. This obviously could mess with AFR and such.
Please input your thoughts.....Thanks!!!!!
DH
Many of us run a catch can in the PCV line (valley to intake manifold line). Then instead of running the passenger valve cover line to the TB (or air bridge on LS2) we put a breather in place. Or cap the vent and put in a breather oil cap.
There seems to be two schools of thoughts.
1. That this is a good idea which allows venting of crank case.
2. That this is a bad idea because it allows unmetered air (not seen by the MAF) to enter the engine .... specifically the intake manifold. This obviously could mess with AFR and such.
Please input your thoughts.....Thanks!!!!!
DH
Last edited by dirty howie; 11-23-2006 at 11:30 PM.
11-23-2006, 07:16 PM
#3
YES!!! A breather AND the PCV system will allow unmetered air to get into the engine, obviously this will make tuning very difficult. Now, if you get a breather filter then you should remove the PCV system.
A breather filter merely opens up the crankcase to the atmosphere, letting out the fluctuations in pressure. The PCV system allows a constant flow of fresh air into the crankcase constantly "cleaning" it out. Breather filters are good in FI applications where there is more blowby, which also provides somewhat clean air into the crankcase.
A breather filter merely opens up the crankcase to the atmosphere, letting out the fluctuations in pressure. The PCV system allows a constant flow of fresh air into the crankcase constantly "cleaning" it out. Breather filters are good in FI applications where there is more blowby, which also provides somewhat clean air into the crankcase.
11-23-2006, 09:08 PM
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You either keep the PCV system, or remove it and use a breather.(or Two, some say it's overkill 
) You can't have both otherwise there will be issues. Also removal of the PCV system will shorten the life of your oil. So be sure to keep tabs on it.
) You can't have both otherwise there will be issues. Also removal of the PCV system will shorten the life of your oil. So be sure to keep tabs on it. 
11-23-2006, 09:12 PM
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Originally Posted by SPRAYED 01
What am i missing, if you block off your vacum ports that used to be part of the pcv how is unmetered air going by?
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11-23-2006, 11:26 PM
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Originally Posted by Ferocity02
YES!!! A breather AND the PCV system will allow unmetered air to get into the engine, obviously this will make tuning very difficult. Now, if you get a breather filter then you should remove the PCV system.
A breather filter merely opens up the crankcase to the atmosphere, letting out the fluctuations in pressure. The PCV system allows a constant flow of fresh air into the crankcase constantly "cleaning" it out. Breather filters are good in FI applications where there is more blowby, which also provides somewhat clean air into the crankcase.
A breather filter merely opens up the crankcase to the atmosphere, letting out the fluctuations in pressure. The PCV system allows a constant flow of fresh air into the crankcase constantly "cleaning" it out. Breather filters are good in FI applications where there is more blowby, which also provides somewhat clean air into the crankcase.
By the way I have run my car with the breather on the valve cover outlet. And with the valve cover outlet connected to my air bridge in front of my LS2 TB. When I run it this way I have a flilter/catch cat in the line. I don't see any observable differences. I will be checking both ways with a scanner (HPTuner) in the neare future.
DH
11-24-2006, 02:00 PM
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Originally Posted by Blue02Ws6
I alreay answered this question I think on the corvetteforum.....Fine don't take my advise... 
This site has a lot more tech minded people for sure. 
This site has a lot more tech minded people for sure. The REASON I am asking here is that I wanted to get more opinions (not that I don't value yours!!).
And I have heard very knowledgable people (engine builders and tuners) tell me different opinions.
Actually I am very surprized that there is any divergence of opinion at all.
I don't know enough about engine internals to figure it out myself
DH
11-24-2006, 02:37 PM
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Originally Posted by dirty howie
The REASON I am asking here is that I wanted to get more opinions (not that I don't value yours!!).
11-25-2006, 12:21 AM
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Originally Posted by Blue02Ws6
I was just kidding with ya. I thought you would get that from my post.
But seriously, I was hoping for some definative info
DH
11-25-2006, 02:14 AM
#14
Originally Posted by dirty howie
In an effort to keep oil out of the intake manifold/combustion chamber.....
Many of us run a catch can in the PCV line (valley to intake manifold line). Then instead of running the passenger valve cover line to the TB (or air bridge on LS2) we put a breather in place. Or cap the vent and put in a breather oil cap.
There seems to be two schools of thoughts.
1. That this is a good idea which allows venting of crank case.
2. That this is a bad idea because it allows unmetered air (not seen by the MAF) to enter the engine .... specifically the intake manifold. This obviously could mess with AFR and such.
Please input your thoughts.....Thanks!!!!!
DH
Many of us run a catch can in the PCV line (valley to intake manifold line). Then instead of running the passenger valve cover line to the TB (or air bridge on LS2) we put a breather in place. Or cap the vent and put in a breather oil cap.
There seems to be two schools of thoughts.
1. That this is a good idea which allows venting of crank case.
2. That this is a bad idea because it allows unmetered air (not seen by the MAF) to enter the engine .... specifically the intake manifold. This obviously could mess with AFR and such.
Please input your thoughts.....Thanks!!!!!
DH
11-25-2006, 08:48 AM
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The air in the crank case is obviously not metered and is not part of the airflow path into the intake. Breathers equalize the pressure between the outside air and the crank case, preventing buildup of pressure in the crankcase from blowby/etc.
The only way I can see any air getting in unmetered would be having a breather hooked up in addition to the stock PCV. The engine vacuum would pull air through the PCV valve into the intake where it enters behind the TB, because the crankcase is not sealed and air would continue to come in via the breather(s). In this case it would be incoming air not read by the MAF, but it would still be read by the MAP so not a big deal for speed density tuned cars.
You really need to do one strategy or the other, not both. Either block off the PCV and put a breather(s) on to equalize the pressure between the crankcase and the atmosphere - OR - use the PCV (positive crankcase ventilation) system to keep pulling on the sealed crankcase to pull out any buildup of pressure. Vacuum pressure inside the crankcase will help with ring seal as well, where you don't get that extra benefit with a breather - however you trade that good ring seal for the necessity to run catch cans and whatnot to try to keep oil out of the intake with the PCV.
Rob (Bad30th)
The only way I can see any air getting in unmetered would be having a breather hooked up in addition to the stock PCV. The engine vacuum would pull air through the PCV valve into the intake where it enters behind the TB, because the crankcase is not sealed and air would continue to come in via the breather(s). In this case it would be incoming air not read by the MAF, but it would still be read by the MAP so not a big deal for speed density tuned cars.
You really need to do one strategy or the other, not both. Either block off the PCV and put a breather(s) on to equalize the pressure between the crankcase and the atmosphere - OR - use the PCV (positive crankcase ventilation) system to keep pulling on the sealed crankcase to pull out any buildup of pressure. Vacuum pressure inside the crankcase will help with ring seal as well, where you don't get that extra benefit with a breather - however you trade that good ring seal for the necessity to run catch cans and whatnot to try to keep oil out of the intake with the PCV.
Rob (Bad30th)
11-25-2006, 09:05 AM
#16
Maybe I'm doing a really bad thing by having both on mine then? I have an LS6 valley cover for my PCV, and I run a breather for my oil cap. I personally don't see how any extra air could be getting in to my engine in any way, shape or form...the PCV is pulling from the valley, and the breather vents whatever is in the passenger side head. I have no fresh air line going to my TB, so I'm pretty sure there is no way unmetered air could be getting in the engine.
Not that it matters, since I tune SD only. Never had a problem, and I don't intend on switching my setup.
Not that it matters, since I tune SD only. Never had a problem, and I don't intend on switching my setup.
11-25-2006, 09:18 AM
#17
Originally Posted by MeentSS02
Maybe I'm doing a really bad thing by having both on mine then? I have an LS6 valley cover for my PCV, and I run a breather for my oil cap. I personally don't see how any extra air could be getting in to my engine in any way, shape or form...the PCV is pulling from the valley, and the breather vents whatever is in the passenger side head. I have no fresh air line going to my TB, so I'm pretty sure there is no way unmetered air could be getting in the engine.
Not that it matters, since I tune SD only. Never had a problem, and I don't intend on switching my setup.
Not that it matters, since I tune SD only. Never had a problem, and I don't intend on switching my setup.
Also of note, running breathers will not avtively evacuate the fumes out of your crankcase like a PCV will. These fumes contaminate your oil and dramaticaly shorten your oil life. Thats why I went back to a PCV setup after trying breathers.
11-25-2006, 09:20 AM
#18
Originally Posted by GuitsBoy
Meents, the valley and both heads all have passages venting into one another so the whole motor shares the same pressures. Youre intake vacuum is pulling air from teh valley cover which in turn is pulling outside air in through the breather. Like you said, its bypassing the MAF, but not that big a deal for you since youre running SD. Its also bypassing the IAC valve, so if youre counts are already low, this may bottom you out.
Also of note, running breathers will not avtively evacuate the fumes out of your crankcase like a PCV will. These fumes contaminate your oil and dramaticaly shorten your oil life. Thats why I went back to a PCV setup after trying breathers.
Also of note, running breathers will not avtively evacuate the fumes out of your crankcase like a PCV will. These fumes contaminate your oil and dramaticaly shorten your oil life. Thats why I went back to a PCV setup after trying breathers.
11-25-2006, 09:31 AM
#20
Originally Posted by MeentSS02
Hmmmmm...after thinking about it some more...wouldn't the setup I have be introducing fresh air into the crank case, but still be evacuating everything since it is pulling a vacuum? Hmmmmmmm...