I have been wondering this for some time now so I decided to ask. I have a breather on each of my valve covers and for some reason I think its a vacuum leak. It been heard getting the car to idle. I thought this may be one factor.
Are valve cover breathers a big vacuum leak?
- Thread starter str8stang036
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One can either use breathers or a PCV but should not use both.
If only breathers are used (no PCV), this works alright.
Or the stock PCV plumbing works for most NA combos. Because PCV is active (vacuum is pulled on the crankcase instead of just venting like breathers), PCV allows greater efficiency.
Anyhow, run one system or the other but do not mix them.
Good luck.
If only breathers are used (no PCV), this works alright.
Or the stock PCV plumbing works for most NA combos. Because PCV is active (vacuum is pulled on the crankcase instead of just venting like breathers), PCV allows greater efficiency.
Anyhow, run one system or the other but do not mix them.
Good luck.
Methodical
Active Member
By what you said with your application ...............
YES ... they are
As always :Word:
Mr. Wizard ... He has the knowledge
Grady
StadEMS3
Dirt-Old 20+Year Member
Really? I did not know that. I have both the (1)breather and the PVC on. Now the dumb question- what do you do to elliminate the PVC? Plug the line or take it out and put a piece of tube in? Will it cause any problems to run both? Will it run better, I thought it was running good? 
ronstang94
Member
Is it ok to just eliminate the PCV valve and tubing at the rear of the intake manifold? I could leave the tube going from the filler neck to the intake tube so that there is still ventilation, but I have oil coming up the PCV valve going into the manifold and fowling my two rear plugs. I would rather not have to put an in line oil seperator in there to fix this problem, but I have to do something. Will it still pass emissions as long as they don't realize the PCV is gone?
So as long as I use the breather method strictly is not a vacuum leak? Or is it still? I have seen some people weld bungs on the valve covers for vacuum lines. Thats why I ask.
A breather alone is not a vacuum leak per se. In other words you should not have issue using breathers and plugging the PCV.
Most of the issue with mixing the two methods comes from unmetered air (air being pulled in through a breather and redistributed for reburn through the PCV. The MAF never knew this air existed).
Most of the issue with mixing the two methods comes from unmetered air (air being pulled in through a breather and redistributed for reburn through the PCV. The MAF never knew this air existed).
95cobraguy
Member
you can also run a breather in the back of the intake where the pcv valve goes. its better to have too much ventilation than not enough.
Mustangless
Member
I don't want to pull my VC off. I am really thinking about just running a breather on my oil fill. Could I put a breather on my lower intake instead of the pcv valve or would that still be a leak?
95strokerPSU
Member
I think the only question that hasn't been answered yet is is one breather sufficient? With our manifold design, it's hard to get a breather on the driver side cover.
Anyone?
Anyone?
Hissin, could you elaborate? Is there more crankcase pressure in a modded motor, overwhelming the design of the stock PCV?
Along those lines, is the reason that a breather does not present a vacuum issue that it generally only expells (assuming the PCV connection is removed) air due to blowby?
Just curious. I had AFM work on and tune my TFS top end kit, and Danny recommended a breather, but I can't recall whether he plugged the PCV. Now I'm curious, but I'll never know, because I cracked my block and had a shop tear it down (a whole 'nother story).
Along those lines, is the reason that a breather does not present a vacuum issue that it generally only expells (assuming the PCV connection is removed) air due to blowby?
Just curious. I had AFM work on and tune my TFS top end kit, and Danny recommended a breather, but I can't recall whether he plugged the PCV. Now I'm curious, but I'll never know, because I cracked my block and had a shop tear it down (a whole 'nother story).
Brad, a modded motor can introduce a couple of added factors. When a leakdown test is done on a fresh mill, it can often display notable (note I didnt say excessive, but notable) blowby.
On modded motors which turn higher RPMs, the air displaced by piston movement can create extra pressure.
When tearing down a motor, seeing a ton of non-solvable grime indicates that there was a bottleneck. The trapped vapors can make a corrosive goo that's tough to remove.
If a PCV system is overwhlelmed, the fluid (air, contaminates, etc) moves at a faster clip, which can allow it to transfer more liquid volume to the intake. Reconfiguring the system to flow more volume at lesser pressures can help. This generally requires multiple points of egressing crankcase vapors. Making shorter runs of plumbing in general can help too (the stock PCV plumbing is kinda long).
I don't think I followed the question in the second paragraph (my fault, not yours). There is indeed less expulsion with a breather (since it passively vents, rather than being connected to intake manifold, which actively sucks the vapors out). Often, just the breather placement is what helps (the vapors have an easier, less convoluted way out).
With a breather set-up, the MAF isnt affected by umetered air. If the PCV and breathers are mixed (remember, the little line from the oil filler to the air-inlet is part of the PCV), then the unmetered air (sometimes called a vac leak) issue arises. On a SD car, it wouldn't matter (it's just an issue with accountability of air mass).
On modded motors which turn higher RPMs, the air displaced by piston movement can create extra pressure.
When tearing down a motor, seeing a ton of non-solvable grime indicates that there was a bottleneck. The trapped vapors can make a corrosive goo that's tough to remove.
If a PCV system is overwhlelmed, the fluid (air, contaminates, etc) moves at a faster clip, which can allow it to transfer more liquid volume to the intake. Reconfiguring the system to flow more volume at lesser pressures can help. This generally requires multiple points of egressing crankcase vapors. Making shorter runs of plumbing in general can help too (the stock PCV plumbing is kinda long).
I don't think I followed the question in the second paragraph (my fault, not yours). There is indeed less expulsion with a breather (since it passively vents, rather than being connected to intake manifold, which actively sucks the vapors out). Often, just the breather placement is what helps (the vapors have an easier, less convoluted way out).
With a breather set-up, the MAF isnt affected by umetered air. If the PCV and breathers are mixed (remember, the little line from the oil filler to the air-inlet is part of the PCV), then the unmetered air (sometimes called a vac leak) issue arises. On a SD car, it wouldn't matter (it's just an issue with accountability of air mass).
if your questions weren't answered here or would just like some more info check this out:
http://www.sn95forums.com/forum/index.php?PHPSESSID=9450f5ac26de94bd009f8ac6cac7d8a8&topic=9567.0
http://www.sn95forums.com/forum/index.php?PHPSESSID=9450f5ac26de94bd009f8ac6cac7d8a8&topic=9567.0
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