# PCV on ABA



## bretthbmx (Jun 20, 2007)

I have a mk4 manifold swap, I've had the PCV routed fine but I was wondering if it would hurt anything to block off the crankcase one? Right now, I have it ran into the intake and just a little breather filter on the valve cover one. The bottom of my air filter is soaked after a couple of months from it though.

Just trying to see if it was bad to block off the crankcase breather?


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## 95shagwag (Feb 14, 2011)

yea you can block the crank case vent off with no problems engine will be fine but not PCV


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## bretthbmx (Jun 20, 2007)

95shagwag said:


> yea you can block the crank case vent off with no problems engine will be fine but not PCV


Okay cool. Guess I'm going to pick up this all metal valve cover with the built in PCV from the junkyard, then run a catch can to the Driverside strut tower.


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## Sycoticmynd29 (Jan 17, 2011)

I've heard that blocking off a PCV can cause some serious oil leaks?


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## ziddey (Apr 16, 2006)

Still venting through the valve cover, just not the block.


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## Sycoticmynd29 (Jan 17, 2011)

But the point of a PCV is to ventilate the crank case, not the valve cover...


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## ziddey (Apr 16, 2006)

same thing. a traditional PCV system runs fresh air through the crankcase (positive). by plugging the crankcase vent, its no longer positive.

venting the "valve cover" is venting the crankcase


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## tacurong (Jul 13, 2009)

*PVC*

true its all connected , its just for emissions


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## Nico. (Oct 8, 2008)

ziddey said:


> same thing. a traditional PCV system runs fresh air through the crankcase (positive). by plugging the crankcase vent, its no longer positive.
> 
> venting the "valve cover" is venting the crankcase


The purpose of a PCV system isn't to run fresh air through the crankcase. It's there to recirculate the left over gases of the combustion chamber back into the intake system to be burnt.


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## WaterWheels (Aug 14, 2005)

Might I suggest a little research and reading up on the subject of PCV systems before making a response like the above. Just a suggestion on my part because what was stated is in fact correct. If the blow-by created by the running engine were just “re-circulated” back into the intake system without anything to fill in the void you would have a negative crankcase pressure (vacuum), which would draw more blow-by (fuel mixture) down into the crankcase causing more problems. I really don't understand what you mean by "left over gasses", just a loose term for blow-by maybe? But you are correct in that the “purpose” is not to draw in fresh air but rather to reduce harmful vapors from exiting into the air. It does however use fresh air drawn in to fill the void in the crankcase left when the contaminated air is drawn out.


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## Nico. (Oct 8, 2008)

WaterWheels said:


> Might I suggest a little research and reading up on the subject of PCV systems before making a response like the above. Just a suggestion on my part because what was stated is in fact correct. If the blow-by created by the running engine were just “re-circulated” back into the intake system without anything to fill in the void you would have a negative crankcase pressure (vacuum), which would draw more blow-by (fuel mixture) down into the crankcase causing more problems. I really don't understand what you mean by "left over gasses", just a loose term for blow-by maybe? But you are correct in that the “purpose” is not to draw in fresh air but rather to reduce harmful vapors from exiting into the air. It does however use fresh air drawn in to fill the void in the crankcase left when the contaminated air is drawn out.


It came out a little funny. it was late. 
Basically i meant the main purpose isn't to run fresh air into the case but to burn the blowby. Blow by = left over gases from the combustion chamber am i wrong? I did a lot of emissions work at my old job it's not fun.


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## bretthbmx (Jun 20, 2007)

Right now I have the crank case breather blocked and the valve cover vented, that's fine, correct?

I need to get this adapter piece off eBay to block the crank case one better.


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## WaterWheels (Aug 14, 2005)

I'll give you credit for poor formulating, but the person you seemed to be correcting, ziddey, did not state that the purpose of the PCV was to introduce fresh air into the crankcase, only that it does. Left-over refers to being left behind or not used, blow-by is not something left over. Like I stated, it could have been, and was it seems just a loose term which I understood even if not really correct. Un-burned fuel in the exhaust I could see being left-over, deposits which the crankcase ventalation can't extract I guess would also be left-over, but blow-by by itself is really in my mind not something left over. But that's what makes the world go round I guess


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