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BDSF
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Discussion Starter #1 (Edited)
So there still seems to be a little confusion on the proper way to have your pcv system modified when boosted (or even n/a). 2J has an excellent write up on the subject, so I'll try not to regurgitate what they have already explained, instead I recommend anyone/everyone read this thoroughly first: https://onedrive.live.com/view.aspx?resid=522D7D76DE502434!5281&cid=522d7d76de502434&app=WordPdf&authkey=!AKUoE3odJTlr7XM


It is important to understand how the pcv system is setup to work on a stock car before attempting to modify it yourself.

There is a one way valve on the back of the valve cover, which I will simply refer to as the "pcv valve". There is also an opening on the drivers side of the valve cover, which I will refer to as the "valve vent".

During idle/partial throttle, vacuum from the intake manifold draws air through the valve cover/crankcase from the pcv valve. Metered air is let in via the valve vent to allow this flow of air to occur. This air MUST BE METERED since it entering the manifold/combustion chambers where the ecu is injecting fuel based on what the mass air flow has already calculated.

At WOT, vacuum in the manifold approaches zero, and an increased amount of blowby is escaping past the piston rings. At this point blowby is now exiting via the pcv valve and also the valve vent because of this.



***Here is the PCV system overview directly from the FSM:







***Here is a diagram of the stock setup (please excuse my poor photoshop drawings):









***A very common mistake (when n/a or boosted) is to put a filter on the valve vent and to cap the inlet on the intake pipe. This is BAD, as you now have unmetered air entering into the intake manifold, equivalent to drilling a hole into your intake manifold, etc.

If your setup is like this, put it back to stock:








***If you followed 2J's write-up, your setup should look like this. This is probably the best way to have the pcv system setup on a boosted car, as you have vacuum from the turbo inlet drawing fresh air into the crankcase, and pulling out blowby/contaminated air that get's trapped in a catch can. Vacuum in your crankcase is a good thing, it keeps all the internal moving parts moving freely which will increase power.
You MUST drill out the pcv valve for this to work correctly and the line running to the turbo inlet MUST be pre-MAF (ie. this won't work on a Turbonetics inlet pipe!)









***Here is another variation of the 2J setup, it has the exact same effect as it just changes where air is entering/exiting the crankcase. Again, the pcv valve MUST be drilled out/removed for this to work properly and the line from the can MUST be pre-MAF.








***Now there are some of us who don't have a turbo inlet pipe or are supercharged without the room for an inlet pipe. In this case you can just vent both lines to a breather tank. You won't have a vacuum in your crankcase, but you can still efficiently evacuate blowby with this setup. This is the exactly how my ProCharged car was setup and it captured a ton of blowby (even without a vacuum source).

 

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BDSF
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Discussion Starter #4
So for cars that are not boosted, best(or only) setup is stock routing with a catch can behind the PCV?
Yes. You could run an additional catch can between the valve vent and intake if you really want to keep everything clean, but most blowby is expelled out of the pcv valve.

You COULD run a setup as shown in the last diagram if you have built or all-out race car that sees a lot of high rpm use, but I wouldn't recommend it if you ever have to pass any type of visual emission inspection.
 

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Great Post Karl, ALLOT of people are confused and dont understand the function of a pcv system and how to modify it (even when 2J has a good write up)

I have the 2J-Racing Version 2 you drew up.
 

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this is a superb explantion
both elegant and clear, thank you

yogi the rouge, has another purpose here
for emissions purposes, i must maintain the pcv function and stock set up
and i don't want oil in my intake
[the idea of oil mixing with nitrous just gives me shudders, true or not]
so this set up is to help keep oil out, but let the engine vacuum continue to assist the pistons
[ read satisfy barry's fear of intake explosions, due to combustion of the oil with nitrous application, this has never happened , he is just old enough to remember the old horrors]

or for those who just want somthing shiny to cover the tranny lol


Please hear this, if you are trying to modify or eliminate the pcv system this is absolutely WRONG
edit too strong a statement
it lacks a second can to eliminate oil coming from the pcv valve at high rpm into the intake manifold
with this provision it does relive pressure and catch oil
the way it is set up now, oil can still enter the intake manifold
i present this here simply to show there are other goals that affect this system, those setups are not incorrect but just have a different purpose

 

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Barry, this is correct for NA. Not for boost. As Karl mentioned. The recirc is done PRE TURBO. For NA its POST MAF.
Oh am I going to have fun with this
1st I’m going to call joe wrong
Lol
That should get peoples attention
no he is not wrong, he is just looking at it from a different perspective
this is half the arguments on here, watch the argument turn into enlightenment as we come to understand these two different perspectives

We both see that at high rpm positive crankcase pressure develops
We are looking at the pressure under the pistons
This comes from air and combustion products pushed past the piston rings, plus normal air pressure
This costs power to push out of the way
If it was possible to produce a vacuum under the pistons on the power stroke [“sucking” the pistons down] we might get more power
Positive pressure under the piston rings also tends to unseat them, causing more blow by the pistons rings and increasing crank case pressure even more

This is the science we agree on

Btw this systems comes from the Sherman tanks of wwII
They needed something to replace the draft tube on the radial engines [came from aircraft] when used on tanks. The engines with draft tubes allowed water to flood the crankcase when the tanks forded streams
Ever wonder how old I really am lol

So obviously it was not designed for hi-po engines

I quote from the original referenced paper
“It just so happens if you read the factory service manual, states that the PCV valve and system is insufficient at WOT and high RPMs and actually has to flow backwards out of the PCV inlet by design because the PCV valve can’t handle the increased blow by flow. High RPM and WOT are exactly when a performance oriented car needs it to be working best.”
This is the reason my catch can is where it is and why joe calls this the correct set up for na

But this doesn’t work for me, evidenced by oil being forced out what is supposed to be the inlet vent for metered air

from my point of view
Imagine a cvt transmission [that worked] keeping my engine at 7000rpm from launch to finish line
At that constant high rpm this system is pumping oil out of every orifice possible
So you would need two catch cans, one for the pcv gaget and one where it is now
And you would still need to understand you are just reliving pressure and not producing vacuum

Joe your turn
 

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As you stated Barry the engine is more efficient and effective with a couple inches of Hg in the crankcase. The best way that I have found and am eventually going to run is with the utilization of a vacuum pump from a desiel. If you run a two inlet/one outlet catch can with one of the inlets hooked up to the gutted PCV valve and the other inlet to the catch can to the valve vent. Then hook the outlet (where the little filter goes) to the vacuum pump with a pressure regulator (or pulse width modulate the vacuum pump). This way you can retain a slight vacuum under the pistons while keeping all of the blow-by/oil out off your engine.
Running this setup for the would be especially beneficial for the F/I guys because they could then run their brake booster off of the vacuum pump since many of them complain about their brake pedal getting hard after entering boost
 

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thats why my set up is "wrong" for NA
it lacks the second can and the pump

with those
the system draws meterd air
removes oil
and lowers crankcase pressure

[for a longer run like Bonneville you might want a drain from the cans back to the crankcase to maintain oil level]
 

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i though the valve vent has a check ball in it too !!!!so basically with a mini filter and no vac on it its doing nothing but building pressure and forcing its more threw the pcv...
i remeber at the bbq you was telling me about this then lucs was telling me that i had to actually drill it out for it to really do something then do the same for the pcv side bu my cars daily driven but beaten on
 

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BDSF
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Discussion Starter #17
Nope, there is no check valve on the valve vent, it is only restricted enough to keep idle from freaking with the stock setup. You aren't building any excess pressure Reggie, but as I mentioned in the last post, it is creating a small vacuum leak.
 

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Yes. You could run an additional catch can between the valve vent and intake if you really want to keep everything clean, but most blowby is expelled out of the pcv valve.
Cool, Thanks for the info. Is it OK to drill out both the valve vent hole and PCV in N/A? Best to leave it stock or maybe drill the valve vent hole larger?

Going to run 2 catch cans either way, 1 for PCV and 1 for the valve vent. When doing my 2J Plenum install, there was oily crap on the TB plate and bore. Not soaking but a little oily and very dirty. Oil was on the old plenum's butterflies too.
 

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BDSF
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Discussion Starter #19
Cool, Thanks for the info. Is it OK to drill out both the valve vent hole and PCV in N/A? Best to leave it stock or maybe drill the valve vent hole larger?

Going to run 2 catch cans either way, 1 for PCV and 1 for the valve vent. When doing my 2J Plenum install, there was oily crap on the TB plate and bore. Not soaking but a little oily and very dirty. Oil was on the old plenum's butterflies too.
Don't drill out anything if you are leaving the lines setup as stock, the car will not idle properly (that's what the restriction in the valve vent is for).
 
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