Closed vs open PCV system?

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Thanatos340

Thanatos340

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How critical is it to have a closed PCV system vs an open PCV system?

I have a new 408 that is just starting to get broke in. Like many "uninformed" before me I did not understand the importance of a PCV system. After chasing a oil pan leak and then reading a good bit here, It seems that just having two pretty breathers on my valve covers is a really bad idea.

Almost all aftermarket VC breathers come with one PCV and One Breather. This would be an open system yet this is what I see on most cars.

How necessary is it that one side (PCV) goes to intake vacuum and the other side goes to Carb Breather for a closed system? Wouldn't you need the positive air flow from the carb breather to really be a "Positive" crankcase ventilation system?

As always, thanks for all the advise. I am still buying my education one wrong part at a time. ;p
 
I know out there in ciber space there is a diagram that will show you how the PCV system works.I'll try to explain without a picture.The PCV valve pulls vapors out of the right side valve cover into the intake at the carb.Thus the left side valve cover will have the breather element in it to "pull" air into the crankcase completing the cycle.As far as closed, all that was done was to "pull air at the air filter housing instead of from the atmosphere.
If I got this wrong,,Hey, I'm old.....:) There ya go Demon 408 got it for you..
 
just 2 breathers is not bad, that is what was used back in the day, and what many a race car uses today. the pcv system was invented so less blowby (pollution) went to the atmosphere. when your foot is to the floor, there is no vacuum, so even with a pcv blowby is vented, and if u have a basic breather it goes to the atmosphere, if u have a breather with a hose going to the air filter most of the pollution gets sucked back in to engine
 
Unless they were really small, or plugged up, the open breathers on each valve cover could not have possibly caused your oil pan to leak.
PCV pretty much has to have the PCV valve on one valve cover, connected to intake vacuum, and one filtered breather on the opposite valve cover. OEM had a simple breather with a hose attached to it that pulled air from inside the air cleaner. Either way works.
 
I'm not sure why you feel there's a difference in systems. One side goes to the carb and has a valve to prevent backfires from going into the crankcase. The other has a breather. Even the factory as 69 mentioned uses a filter at the valve cover. otherwise it pulls air from a factory air cleaner, but it's outside the element and thus unfiltered air that enters it there.
Also - two breathers will work - it can just get messy over time. Leaks and crankcase pressure don't come from the PCV or lack thereof. It comes from blowby, aka the rings. They take time to seat, and some may never seat fully depending on the machining and assembly practices of the builder.
 
Both sides of the PCV system are filtered. See this diagram. One side uses the air filter in reverse, but it does use the filter.
 

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X2^ exactly how the pcv system on my 340 is set up, left(drivers side) valve cover has pcv valve and hose going to port on carb, other valve cover has a breather and hose going to the air cleaner
 
71DodgeDemon340 said:
X2^ exactly how the pcv system on my 340 is set up, left(drivers side) valve cover has pcv valve and hose going to port on carb, other valve cover has a breather and hose going to the air cleaner
Click to expand...

at idle or low rpm, the pcv valve is working. at hi rpm where there is no vacuum , the breather will be working because of higher vacuum up there. I have 2 breathers on my 505, but am going to convert to the aforemention set up. should have great vacuum w/ gapless rings.
 
The air, entering the hose within the factory air cleaner assembly, is NOT filtered. See the attached pic. The nipple is placed outside the filter. It's outside the element on these. The filter for the PCV is in the breather. So it's unfiltered until it passes through the breather. That was my point.
 

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Taken to the extreme there are belt driven vacuum pumps used by many racers for crankcase evacuation. Some are to help on boosted applications and some claim it is like supercharging in reverse because it is sucking on the bottom of the piston. Since there are as many pistons going up as there are coming down that doesn't really add up but they do use them and go fast plus there are much fewer leaks.
 
The vacuum pumps are for aiding ring seal. Similar to gas porting the piston to have the combustion gasses push the rings against the wall. They extend the rpm range, and reduce losses that will always be a part of an internal combustion engine. The leakage occurs during the compression and power strokes, and to a much less extent the intake stroke. So there's a lot more leakage out, than in... if that makes sense...
 
moper said:
The air, entering the hose within the factory air cleaner assembly, is NOT filtered. See the attached pic. The nipple is placed outside the filter. It's outside the element on these. The filter for the PCV is in the breather. So it's unfiltered until it passes through the breather. That was my point.
Click to expand...

And that is exactly why I built my PCV system the way I did.
On one valvecover it has the PCV valve, and on the other a breather with a hose going up under the chrome base of the filter housing (inside the filter area)

The main reason for doing it in the first place was to help clean the bad (acidic gasses) out of the engine and the air being pulled in is actual filtered air.
Most of the OEM PCV systems used a small piece of foam that somewhat filtered the air, but it was on the outside of the actual filter element and I was not comfortable with that.
 

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