[PortDover335xi]

I bought a new PCV valve with replacement Cap, received it in the mail today. Just curious how it works. Looking at how the valve fits into the cap where does the pressure go the valve is supposed to control?? Any PCV valves I see on other cars it's usually attached to a hose that I think goes back into the intake.

[Emilime75]

It's all internal within the valve cover. I don't fully understand it myself, but I believe it ends up coming out/through the flapper valve(crankcase vent) and into the rear inlet.

[Sgop335]

Originally Posted by PortDover335xi

I bought a new PCV valve with replacement Cap, received it in the mail today. Just curious how it works. Looking at how the valve fits into the cap where does the pressure go the valve is supposed to control?? Any PCV valves I see on other cars it's usually attached to a hose that I think goes back into the intake.

Good question. There is a hidden port/hole in the valve cover right where the threads end for the CAP. One can feel the port with fingers. This port goes to the intake manifold that communicates vacuum or pressure to the valve.

[PortDover335xi]

Ok cool thanks for the info! Gonna install today.

[dpaul]

Originally Posted by Emilime75

It's all internal within the valve cover. I don't fully understand it myself, but I believe it ends up coming out/through the flapper valve(crankcase vent) and into the rear inlet.

When the intake manifold is below atmospheric pressure (at idle and part throttle), air flows from the rear inlet back through a small hole in the flapper into the valve cover and thus crankcase. This partially makes up for what is sucked though the check valve into the intake manifold though ports internal to the valve cover, as described above by Sgop335. I presume the idea is that crankcase negative pressure should not become excessive.

During boost, where the manifold is above atmospheric pressure, the check valve is closed and the flapper is fully opened so crankcase positive pressure developing from blowby is vented though the flapper in the opposite direction from described above, into the intake pipe.

For the sake of completeness and to test my understanding, the BMS catch can collects only under boost and since most of us don't spend all that much time at full throttle, it generally doesn't collect all that much oil. The low pressure side must be "externalized" in order to add a catch can to it - I think this was first done by Rob Beck, who has patiently explained how the N54 PCV system works, over and over again, to idiots like me who cannot seem to hold it all in our heads at one time. This externalized low pressure system collects quite a bit of oil and oil/water vapor condensate, in my experience.

Someone please correct me if I've got something wrong.

[PortDover335xi]

While I got you guys here, take a look at this photo from when I took the engine cover off. Does this look like a valve cover leak? Check out the ports above the ignition coils there's oil collecting in all 6. On a scale of 1-10 10 being bad.

[Emilime75]

Generally speaking, if there's oil down there and it isn't from sloppy fill ups, it's a leaky valve cover. There's also the possibility of a cracked valve cover, which is somewhat common.

[Emilime75]

Originally Posted by dpaul

When the intake manifold is below atmospheric pressure (at idle and part throttle), air flows from the rear inlet back through a small hole in the flapper into the valve cover and thus crankcase. This partially makes up for what is sucked though the check valve into the intake manifold though ports internal to the valve cover, as described above by Sgop335. I presume the idea is that crankcase negative pressure should not become excessive.

During boost, where the manifold is above atmospheric pressure, the check valve is closed and the flapper is fully opened so crankcase positive pressure developing from blowby is vented though the flapper in the opposite direction from described above, into the intake pipe.

For the sake of completeness and to test my understanding, the BMS catch can collects only under boost and since most of us don't spend all that much time at full throttle, it generally doesn't collect all that much oil. The low pressure side must be "externalized" in order to add a catch can to it - I think this was first done by Rob Beck, who has patiently explained how the N54 PCV system works, over and over again, to idiots like me who cannot seem to hold it all in our heads at one time. This externalized low pressure system collects quite a bit of oil and oil/water vapor condensate, in my experience.

Someone please correct me if I've got something wrong.

Great explanation, and I am also one of those who needs to hear/read this a thousand times before it becomes actual knowledge. I've read and asked several questions regarding the RB external PCV+OCC setup and ended up buying it, just haven't installed yet.

[PortDover335xi]

Another question about the new PCV I installed, the factory cap has what I call 4 teeth that protrude from the open end my maybe a 16th of an inch. So when the pcv valve is sitting in the cap there's an opening. The aftermarket valve/cap setup I bought sits flush together, is this a bad thing?

[Sgop335]

Originally Posted by dpaul

When the intake manifold is below atmospheric pressure (at idle and part throttle), air flows from the rear inlet back through a small hole in the flapper into the valve cover and thus crankcase. This partially makes up for what is sucked though the check valve into the intake manifold though ports internal to the valve cover, as described above by Sgop335. I presume the idea is that crankcase negative pressure should not become excessive.

During boost, where the manifold is above atmospheric pressure, the check valve is closed and the flapper is fully opened so crankcase positive pressure developing from blowby is vented though the flapper in the opposite direction from described above, into the intake pipe.

For the sake of completeness and to test my understanding, the BMS catch can collects only under boost and since most of us don't spend all that much time at full throttle, it generally doesn't collect all that much oil. The low pressure side must be "externalized" in order to add a catch can to it - I think this was first done by Rob Beck, who has patiently explained how the N54 PCV system works, over and over again, to idiots like me who cannot seem to hold it all in our heads at one time. This externalized low pressure system collects quite a bit of oil and oil/water vapor condensate, in my experience.

Someone please correct me if I've got something wrong.

I once had the same understanding. But something important i want to point is that the n54 uses the flapper valve route under boost (as you say) and also Idle (e.g. -8.2psi)!! It appears the only time the other route (to intake manifold) is used is for Decel (e.g. -11psi). I know trying to wrap your head around. If you like a little evidence i can provide from bmws engine mechanical literature. But the best evidence was when i measured cc pressure at idle (

[arkie6]

With the the N54 PCV valve when the engine is operating under vacuum (vs. boost), crankcase gases are pulled through the center of the PCV valve outward into the cap, then over the tip of the PCV valve nipple and back into channels in the valve cover. A small amount of fresh air is admitted into the crankcase via the small hole in the flapper valve. These ventilation channels lead to six (6) individual small ports in the aluminum head right before each cylinder's intake valves. This is the most direct cause for carbon buildup on the intake valves and the need to periodically walnut blast the intake valves. You can plug the ports in the head with a tap and setscrews. This eliminates the vacuum side PCV unless you install an external PCV valve arrangement (either aftermarket or DIY).

When the engine is under positive boost pressure, the 6 ports in the head and channels in the valve cover provide this positive pressure to the PCV valve which closes if it is working properly to prevent pressurizing the crankcase. Under boost with the PCV valve closed, any need for crankcase ventilation is through the flapper valve into the rear turbo inlet pipe.

[arkie6]

Originally Posted by dpaul

When the intake manifold is below atmospheric pressure (at idle and part throttle), air flows from the rear inlet back through a small hole in the flapper into the valve cover and thus crankcase. This partially makes up for what is sucked though the check valve into the intake manifold though ports internal to the valve cover, as described above by Sgop335. I presume the idea is that crankcase negative pressure should not become excessive.

During boost, where the manifold is above atmospheric pressure, the check valve is closed and the flapper is fully opened so crankcase positive pressure developing from blowby is vented though the flapper in the opposite direction from described above, into the intake pipe.

For the sake of completeness and to test my understanding, the BMS catch can collects only under boost and since most of us don't spend all that much time at full throttle, it generally doesn't collect all that much oil. The low pressure side must be "externalized" in order to add a catch can to it - I think this was first done by Rob Beck, who has patiently explained how the N54 PCV system works, over and over again, to idiots like me who cannot seem to hold it all in our heads at one time. This externalized low pressure system collects quite a bit of oil and oil/water vapor condensate, in my experience.

Someone please correct me if I've got something wrong.

I doubt the flapper valve is ever fully opened under boost unless you have a lot of piston ring blowby. It probably just flutters open as necessary under boost as I doubt most engines have enough flow to cause it to swing wide open.

I have a JB4 installed and am running my fuel gauge as my boost gauge. When I'm running 75-80 MPH down the interstate with the cruise control on, I'm generally showing 1-2 psi boost. Under this condition, the PCV valve should be closed and all ventilation is coming through the flapper valve.

The externalized PCV system and catch can likely catches most of the oil during cold startup and the first few miles of driving prior to the piston ring end gaps closing up when they approach normal operating temperature.

[dpaul]

Originally Posted by arkie6

I doubt the flapper valve is ever fully opened under boost unless you have a lot of piston ring blowby. It probably just flutters open as necessary under boost as I doubt most engines have enough flow to cause it to swing wide open.

I have a JB4 installed and am running my fuel gauge as my boost gauge. When I'm running 75-80 MPH down the interstate with the cruise control on, I'm generally showing 1-2 psi boost. Under this condition, the PCV valve should be closed and all ventilation is coming through the flapper valve.

The externalized PCV system and catch can likely catches most of the oil during cold startup and the first few miles of driving prior to the piston ring end gaps closing up when they approach normal operating temperature.

Unfortunately for me, most of my driving is not running down the interstate at 80mph. It's slogging through traffic and stop lights. I collect much more volume from the externalized negative pressure circuit than the boost circuit. I suppose it is possible that the externalized circui is functioning mainly during the first few miles of driving. But that is not the impression I get.

In regards to the flapper, I'm not sure what the difference between fully open and "flutters" open is but it certainly doesn't take much effort to fully open it. It will fall fully open under it's own weight (when the vent hose is out of the car and positioned correctly). Of course, I have no quantitative measure regarding the extent or timing of flapper valve opening.

[dpaul]

Originally Posted by Sgop335

I once had the same understanding. But something important i want to point is that the n54 uses the flapper valve route under boost (as you say) and also Idle (e.g. -8.2psi)!! It appears the only time the other route (to intake manifold) is used is for Decel (e.g. -11psi). I know trying to wrap your head around. If you like a little evidence i can provide from bmws engine mechanical literature. But the best evidence was when i measured cc pressure at idle (

Thanks, it would be interesting to read that literature

[Sgop335]

Originally Posted by dpaul

Thanks, it would be interesting to read that literature

Yes, here is part of it that basically says Deceleration is one mode and "Acceleration or Idling" is the other mode...little strange

[gde061]

I have been trying to get my head around how the plumbing on my car was done when the intake was upgraded -- the flapper tube from the PCV high pressure side (I think I got that right after reading this post) is disconnected at the back of the engine. Ignoring for the moment pollution issues (the plan is for it to be more track car and less daily driver), what is the risk to a VTA setup? I found somewhere on another site a discussion of doing it this way (there's a link in my original post here)

Also, is there a sticky or can someone provide links to the explanations of the PCV / low circuit externalization mentioned by Rob Beck? I am also having some trouble making out the text in the from the BMWs engine mechanical literature above and I think reading that would help... I really want to try to get the best solution -- my mechanic says go back to a stock intake and reconnect the flapper tube as BMW designed it. Not my preference.

[arkie6]

Originally Posted by gde061

I have been trying to get my head around how the plumbing on my car was done when the intake was upgraded -- the flapper tube from the PCV high pressure side (I think I got that right after reading this post) is disconnected at the back of the engine. Ignoring for the moment pollution issues (the plan is for it to be more track car and less daily driver), what is the risk to a VTA setup? I found somewhere on another site a discussion of doing it this way (there's a link in my original post here)

Also, is there a sticky or can someone provide links to the explanations of the PCV / low circuit externalization mentioned by Rob Beck? I am also having some trouble making out the text in the from the BMWs engine mechanical literature above and I think reading that would help... I really want to try to get the best solution -- my mechanic says go back to a stock intake and reconnect the flapper tube as BMW designed it. Not my preference.

I provided an explanation of how the BMW N54 PCV system works in your original post linked above.

[gde061]

Originally Posted by arkie6

I provided an explanation of how the BMW N54 PCV system works in your original post linked above.

I read your post... Very helpful, thanks. After I went back to the diagrams above and it made more sense, but I'm a little confused because usually the terms I recognize are "flapper valve" and "PCV valve". While in the pic's above it talks about "check valves". Which parts in these diagrams represent the PCV and the flapper, if someone can help with that?

Thanks.

[Sgop335]

Originally Posted by gde061

I read your post... Very helpful, thanks. After I went back to the diagrams above and it made more sense, but I'm a little confused because usually the terms I recognize are "flapper valve" and "PCV valve". While in the pic's above it talks about "check valves". Which parts in these diagrams represent the PCV and the flapper, if someone can help with that?

Thanks.

I will say there are errors in the description above if anyone catches them. Regardless #12 is your flapper valve and #14 is your "pcv" valve

[arkie6]

Originally Posted by gde061

I read your post... Very helpful, thanks. After I went back to the diagrams above and it made more sense, but I'm a little confused because usually the terms I recognize are "flapper valve" and "PCV valve". While in the pic's above it talks about "check valves". Which parts in these diagrams represent the PCV and the flapper, if someone can help with that?

Thanks.

Both the PCV valve and flapper valve are technically "check valves". In the diagram above, 14 is supposed to represent the PCV valve and 12 is supposed to represent the flapper valve.