Not sure on how the F-body setups are, but on the C5/ATI, the PCV is configured as follows:
PVC is hooked up to the nipple on the manifold, rear of the TB
Fresh air feed runs to the airbox, in front of the S/C
TB Fresh air is capped.

Under vacuum, the manifold pulls crankcase air from the PCV line. This is then equalized with the fresh air being pulled from the airbox, into the front of the valve cover.

Now, put the car under boost. The positive pressures in the manifold should push past the weak stock PCV valve, while at the same time I believe that the ATI will create a vacuum situation inside the airbox at WOT. I would think that this would then pull air from the front of the passenger side valve cover, essentially reversing the flow of the PCV system.

What to fix this?
Putting a checkvalve(McMaster-Carr) in the PCV line, before the intake manifold will stop the blow-by experienced by the stock PCV valve. However I would think that the crankcase gasses would be both pulled(airbox vacuum) and pushed(ring blow-by) out of the fresh air vent in to the airbox. Although this may be minimal if the check valve is in place.

Some of the issues that I am looking at is that with this configuration, at idle, is that the PCV functions normally, but the engine is still getting unmetered air. Under a boosted condition, the PCV should stop functioning or minimally move air from the fresh air vent to the airbox.

Is this fine, or should I look at doing other changes. I can put a breather in place of the fresh air inlet on the valve cover. This would permit the crankcase to release any blow-by and remove the airbox as a vacuum source at WOT. The downside is that the engine is still seeing unmetered air.

I can live with the unmetered air while the engine is a vacuum, but my main question is if the PCV should operate at WOT or not. At WOT, do we just need a way to vent any positive crank case pressure, or is vacuum needed to maintain ring seal<--- not sure on this... thought I read it somewhere. If ring seal is not an issue, then I can simply run a PCV setup as follows:

PCV Out to catch can
Catch can to intake manifold, rear of TB
Check valve and Filter in-line between can and manifold
TB fresh air tube capped
Valve cover fresh air inlet ran to a breather.

This will prevent blow-by past the stock PCV valve, reducing positive crank case pressures while under boost, at the same time pulling crank case gas when the manifold is under vacuum. The fresh air breather will not see a vacuum condition, as running to the ATI airbox would, preventing the PCV system from reversing. Any positive crank case pressure would vent out the breather if the crank case pressures are lower than those ovserved in the manifold.

One other solution I was looking at, if the PCV should see vacuum at WOT is to do all of the above, but split the line exiting the catch can/filter. One line would run to the manifolf with a check valve in-line. The other line would run to the airbox, also with a check valve in place. With this setup, at idle, the check valve running to the manifold would be open, while the check valve running to the airbox would be closed. At WOT, while the manifold is under boost, the check valve running to the manifold would close and the vacuum in the airbox would open the check valve in the line running to it. With this setup, the PCV outlet would see vacuum both at idle and at boost. Fresh air would be drawn from a breather hooked up to the fresh air inlet on the passenger side valve cover.

I know its long... Any opinions?

 

i have tried a bunch of pcv set ups and crankcase vaccum set ups.. what i ended up withe is just a vent to atmosphere off the valvecover.

any stock style pcv system only helps you at idle unless you are looking for something other than performance (gm's intention) at wide open you are only as good as or worse than a vent to atmosphere.

 

I have my (99 valve covers) pcv hoses looping from the rear of the driver's side to the back of the passenger side, and I have a hose coming off the front part of the passenger cover, venting to open air but I have the filter running way far away from the motor. I have the TB inlet capped off.

 

I also have a c5 and have been contenplating a PCV solution.

I had my crankcase pressurized so much that it blew the dipstick, but it did not seem like any oil came out the inlet line (the one going to the air filter/box). I'm not sure why this is, but I'm assuming it resist air going out that direction for some reason. Do all those lines just go to the valve covers, or do they route down into the crankcase in some specific fashion? I know that people without a check valve in the PCV get oil out this line, but I have never heard of it with a check valve in place.

Here is what I did to resolve the problem (and it seems to have worked).

The PCV line comes out of the manifold and through a check valve and then the PCV valve. After that it goes to a catch filter and then there is a T. One side of the T goes to the valve cover and the other goes to a normally closed solenoid inlet. The solenoid outlet then goes to an open air catch can. The solenoid only opens under boost via a simple pressure switch. This allows regular positive ventilation under non boost, and a breather when under boost.

Another option is an EVAP setup that creates a vacuum from the exhaust header for positive ventalation under boost. I'm still looking for details on one of these. I have another post in this section with "blowby" in the title asking for more details.

 

The header aspiration thingy will only work well if you are running open headers/high exhaust volume. Perfect on a drag only race car, but in a street car it will not do much/may hurt. It depends on high flow and 0/low backpressure to work.

 

Thanks for the replies. What I had originally decided on was to run a setup similar to Mightymouse and PSJ. I was going to run the PCV out to the manifold, with a check valve inline and then run the fresh air to a breather.

But after looking at QuickSilver's setup I noted a few differences. No fresh air and also no unmetered air entering the motor. The unmetered air part is a plus, but without a fresh air inlet I dont think think that any air will be pulled, other than blow-by while the engine is in a state of vacuum. Any air pulled will create a vacuum situation in the crankcase until the pressures equalize. QS, this is not a rip on your setup, I'm just pointing out something that you may have overlooked. Trying to help us both.

 

No offense taken, but I do have a fresh air source.

Let me explain my old setup and then my new setup. A discovery that I just made tonight helps explain exactly what has been going on. Although, I don't have a perfect solution yet.

My old setup consisted of the valve cover inlet going down to my air filter and the valve cover outlets going to the PCV valve and intake manifold (with a check valve to keep boost from directly pressurizing the crankcase). This seemed to work fine until the cooler weather caused a boost increase and the dipstick blew out and sprayed oil in the engine bay (I probably also just have more blowby in the motor now). In thinking about the setup, I assumed that the PCV system would reverse under boost, and that blowby gasses would be evacuated out the inlet (since it becomes a slight vacuum and the outlet is blocked). This made me think that I had a ringland or piston problem and that the blowby just overtook the evacuation capabilities of that small outlet hose. I pulled off my filter and inlet bridge to check for oily residue and there seemed to be none. This made me realize that there was very little if any evacuation taking place under boost and that I could eliminate the dipstick blowout problem by just providing an exit on the outlet side while under boost.

I decided to try something and this is what I came up with.
The valve cover outlets now go to a T, where one side of the T goes to the PCV valve and intake manifold, and the other side goes to a solenoid and eventually to an open air catch can. The solenoid only opens under boost. My thought was that this would allow for vacuum and normal PCV under non-boost, but would allow for breathing of the crankcase pressure out into the catch can during boost conditions. Testing this setup in various conditions showed that the dipstick no longer blew out and that some decent ventilation seemed to be taking place. I put the car on the dyno and took it to the track. It seemed to run fine, except there was now a little KR that had not previously existed. So I pulled off the blower inlet tonight and guess what was there? Sure enough, a nasty thin coat of oily residue. So I’m pretty sure that my new open air catch can is just acting as an air inlet (under boost) and that the system is reversing and the gasses are going straight into my intake and causing the motor to knock. Not to mention contaminating my intercooler….

The only good solution I can think of is an external vacuum pump with an isolated inlet breather and outlet dump. In the meantime, I’ll probably just put a catch can and filter on the inlet side to keep that nasty stuff out of my intake.

Anyone have any ideas on where I can find an electric vacuum pump. Part#s and sources would be greatly appreciated.

Wait, I might already have on on the car. What about the A.I.R pump.

 

I just drew out your setup and think I may have found the problem... although I'm not sure. You stated, "...The valve cover outlets now go to a T..." I'm assuming that you mean that the PCV out(stock line) goes to a T and that the fresh air inlet at the front of the valve cover runs to the airbox, ahead of the S/C. If this is the case, I could potentially see a possibility for oil consumption.

Assuming that all the check valves work properly, under a boost condition the only line that should be open is the vent from the rear passenger side PCV out to the catch can/breather. The other half of the T, going to the manifold should be closed at boost. The potential problem I see with this is that under boost the oil in the motor is going to move to the back of the motor from the vehicles acceleration, right where the pressure vent line is located. I would think that there would be a greater chance for oil to enter the line as pressures are released from this location. Now when you let off the gas, closing the line running from the T to the catch can, the rest of the line functions like the stock PCV. Any oil left in the line would then be pulled in the direction of the manifold.

One sollution may be to move the breather to the front fresh air tube on the valvecover.
Setup something like this:
Rear PCV out to check-valve(-->) to Manifold, rear of TB
Fresh Air tube, front passenger side valve cover, to a T
T out #1 to checkvalve(<---) to airbox(fresh air source)
T out #2 to checkvalve(--->) to breather(crankcase pressure vent)

This would allow the same funcion as stock, but would allow for the excess crankcase pressures at boost to be vented from the front of the motor, rather than the back where oil can collect.

 

I've also been doing some checking on the net and the only thing I can find is that the PCV system is only for emissions and to let the oil last longer. For some reason I thought it had something to do with ring sealing, but couldnt find any info on it. Anyone know anything about this?

If its only for emissions, I'll simply close up everything and just run a breather as a vent for the crankcase pressure. I'll just have to change the oil more frequently.

 

Here is what it looks like
PCV

I think the inlet is getting a decent vacuum under boost and the blowby gasses are being sucked into the air filter. Blowby gasses are nasty and oily by nature and will cause KR.

The sealed catch filter in the drawing above is pretty much dry. This tells me that not much stuff is going in that direction.

I'm going to try to rig up a vacuum gauge tonight (on the inlet) and see what it says under different conditions.

 

I just got back from testing a breather only setup. Capped off everything and hooked up a breather to the front passenger side valve cover. With this setup, there is no positive evap, only a way to vent any ring blow-by. Additionally, no un-metered air is entering the motor.

What I observed was:
1. Idle vacuum remained unchanged(autometer gauge)
2. Driveability improved(idle + part throttle)
3. LTerms at Idle and Part Throttle became closer

Prior to the breather only, when the PCV was bringing in unmetered air, my LTerms at idle were right around +1.6, while those at part throttle were around -4 to -6. Now LTerms at idle are -2.6, much closer to what they are at part throttle. I originally thought this difference in LTerms was attributed to the SVO injectors, but now I believe it is directly related to the unmetered air entering through the modified PCV setup, as laid out by ATI.

Looks like I'm just going to keep the PCV disconnected and run a breather for a vent, unless I find a good reason for needing one... other than for emissions.