one pvc, or two
Thread Starter
Melting Slicks
Joined: Jun 2004
Posts: 2,077
Likes: 0
From: westmoreland N.H.
one pvc, or two
i'm toying with the idea of two pvc's for more crankcase ventilation. my breather has a tendancy to weep a little oil, and was wondering if a second pvc will help with this problem... the current pvc is new.. 
Drifting
Joined: Mar 2005
Posts: 1,806
Likes: 3
From: Burlington WI
??
If you put a pcv valve in both valve covers you will be putting full manifold vacuum on your crankcase.
The air needs to flow in one side and then out through the pcv.
If your breather cap is loading with oil, that tells me your pcv valve isnt working properly and needs to be replaced.
The air needs to flow in one side and then out through the pcv.
If your breather cap is loading with oil, that tells me your pcv valve isnt working properly and needs to be replaced.
C6 the C5 of tomorrow
Joined: Nov 2000
Posts: 6,665
Likes: 2
From: Twin Cities Minnesota
I disagree. Pulling a vacuum is a god thing. T PCV's would be great except that manifold vacuum drops to zero at WOT.
The best arangement is a tube that connects to the clean side of the airfilter, just like stock. That way at WOT the fumes get burned and don't mess up the engine compartment
The best arangement is a tube that connects to the clean side of the airfilter, just like stock. That way at WOT the fumes get burned and don't mess up the engine compartment
Drifting
Joined: Mar 2005
Posts: 1,806
Likes: 3
From: Burlington WI
Originally Posted by 427V8
I disagree. Pulling a vacuum is a god thing. T PCV's would be great except that manifold vacuum drops to zero at WOT.
The best arangement is a tube that connects to the clean side of the airfilter, just like stock. That way at WOT the fumes get burned and don't mess up the engine compartment
The best arangement is a tube that connects to the clean side of the airfilter, just like stock. That way at WOT the fumes get burned and don't mess up the engine compartment
There are valve cover breathers with a hose fitting for that purpose.
I hadnt really thaought that all the way through.
Chris B
C6 the C5 of tomorrow
Joined: Nov 2000
Posts: 6,665
Likes: 2
From: Twin Cities Minnesota
Um it's a vacuum...
The point of a pcv system is to pull the blowby gasses out of the crankcase otherwise it will actually pressurise untill it does vent.
Pulling vacuum is a good thing, racers do it to reduce windage, that means the crankshaft is acting like a fan on the air / oil in the crankcase.
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Le Mans Master
Joined: Jul 2005
Posts: 5,752
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From: Austin Texas
If you are running an aggressive camshaft with low idle vacuum, your p.c.v. system may not be able to keep up with the blow-by. Then you may need to plumb 2 breathers, 1 to each exhaust collector tube (only applies to vettes with headers). Or, add a vacuum pump for the crank-case... but that's getting off track for this thread..IMO! 
Drifting
Joined: Nov 2001
Posts: 1,469
Likes: 6
From: 68 427 4.11s Roadster
Your missing the point. For there to be flow you have to have the air come in one spot and out the other. Vacuum is the out, so where is the in? A dirty gasket?
If the in (breather) is on the same cover as the vacuum you don't have any vacuum on the other cover. Your vacuum is sucking only through that valve cover. The rest of the engine is bypassed.
Reverse it. Your carb is supplying pressure. The breather is letting it out. flow.
If you pressurize both covers there is no air flow.
If you put a breather on one cover there won't be any pressure in the closed cover since it won't go there. It won't follow the path of most resistance. It will go in the cover and right out the breather.
If the in (breather) is on the same cover as the vacuum you don't have any vacuum on the other cover. Your vacuum is sucking only through that valve cover. The rest of the engine is bypassed.
Reverse it. Your carb is supplying pressure. The breather is letting it out. flow.
If you pressurize both covers there is no air flow.
If you put a breather on one cover there won't be any pressure in the closed cover since it won't go there. It won't follow the path of most resistance. It will go in the cover and right out the breather.