Catch Can Setup With Blow Through Set-Up?

[SFRacingGST]

Here is my problem: I have been heavily reading up on how to properly run the PCV system with catch can’s inline. However the problem I am running into is that I have a blow through setup so when I set it up like the stock configuration, the system pulls un-metered air through the PCV valve from the air intake (which is before my mas). Originally I had the PCV line and valve cover line routed to a vented RR&E catch can. That was not an ideal way of running because there was no vacuum pulling the excess crank pressure out. Right now I have it set up better that just running to a can. I took off the breather on the RR&E catch can and put 1/4 inch to 3/8 90 degrees fitting on the top. However, I know this isn’t really effective either, especially at idle. In the dsmlink forums’ they stated that they have tested that the line coming from the air intake will only pulls 2psi of vacuum at full boost from the intake side, comparing that to 10 (heavy cams at idle) or 20 (the vac on a decal).
I need a better way of routing my PCV system. I had came to this conclusion when oil was leaking out of the oil cap seal and around my valve cover, also when my oil started smelling like fuel (which isn’t good at all!). I have came up with several ideas, however none of them are perfect yet.

 

[SFRacingGST]

The check valve that is green (that you can't read the writing above) is a USPlastic Check valve 64175.( http://www.usplastic.com/catalog/pr...e=usplastic&category_name=45&product_id=15641)

The second picture is a simplified version of the first with one can.

The flaw with this setup is that the PCV needs to draw fresh air in from somewhere after the mas. The stock configuration does it from the intake at vacuum. Any ideas?? If you have a MAFT, how are you running yours??

I need something with less variable if possible.

 

[turbosax2]

My brother just switched to blow through on his car and we have 2 Husky catch cans and a Mcmaster check valve set up like your first picture (which is basically the stock set up with 2 catch cans thrown in the middle of the lines). The car hasn't run at all yet so I can't vouch for how well it will work.

I'm somewhat confused with what you're saying. "the system pulls un-metered air through the PCV valve from the air intake (which is before my mas)" - The pcv connects to the intake manifold, not the air intake pipe, so in stock configuration or in blow through, the vacuum from the intake manifold is still pulling air through the pcv, right?

Somebody please correct me I'm wrong here, just trying to make sense of what you're saying.

Edit: I said we had the catch cans set up like in your first pic, but actually we don't have a check valve on the line from the vc to air intake pipe.

 

[turbosax2]

Have you read these threads?

http://www.dsmtuners.com/forums/showthread.php?t=254437
http://www.dsmtuners.com/forums/showthread.php?t=229338

 

[SFRacingGST]

Thanks for the two threads turbosax but that is where my whole adventure had started. I tried the whole 2 catch can setup like the one in VFAQ and in those threads. The way stock runs it, with a catch can in each line and a check valve on the PCV line between the can and intake manifold.

Here is the problem. The PCV valve opens under vacuum. During idle, the vacuum would be drawing in fresh air (through the valve cover breather and from the air intake) which at this point would be unmetered air because it is before the MAS.
I noticed a problem because my dsm airflow meters had to be ajusted alot after setting the system up like the write up in the vfaq. Under boost i would not have a problem because of the check valve.

Here is what i don't get. Even if you have a stock dsm with a blowthrough setup on it, it sould still do the same at idle. It is hard to believe that all these people have a MAFT, and this issue hasn't been mentioned before.

 

[SFRacingGST]

No one experienced this?

 

[BaileyBoy]

old thread i know, but I am curious if you ever found an answer for this. I am looking to just throw in a nipple in my IC piping because I made my own turbo inlet pipe....so no intake hose provisions....should I put the nippe after my maf, or still put it on the turbo inlet pipe. I just dont want to run into the unmetered air problem...

 

[WillRaceForBeer]

Sorry to bring this back, but I am working on a solution to this exact issue and felt this is the place to share and prompt discussion.

The main problem as the OP points out is that for those of us running blow through on a DD, we suffer some drive-ability issues brought on by the intake of unmetered air, and this seems to really become an issue in sub-freezing temperatures. Eliminating PCV all together is a solution, but not a good one for DD vehicles.

Ideally I want to keep the PCV functionality intact for Idle/Cruise without introducing unmetered air into the system. This means that during Idle/Cruise the source of fresh air will be immediately after the GM Maf, and the vacuum will need to be a stronger vacuum then that which is present before the TB, which is the same as stock, the Intake Manifold. During WOT I want to avoid the loss of metered air, but still have a vacuum on the crank case.

I mocked up a solution tonight that allows fresh metered air to be pulled in at Idle/Cruise, while still preventing pressurized air from entering the crank case. The key here is a pressure actuated solenoid that closes off the fresh air source. I studied a number of sources on our Emmisions parts, and it seems that in theory the EVAP solenoid on the firewall will perform the way that is required. If not it may be possible to use a Hobbs switch or similar to operate an electronic solenoid (perhaps one that we already have)

Here is what I am proposing during Idle/Cruise:

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And during WOT

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Something to keep in mind:
The vacuum hoses between the fresh air source => evap => VC and VC => IM are stock diameter because the flow rate at Idle/Cruise has not changed. The vacuum hoses to the CC and from the CC => Intake are larger diameter to account for high boost applications during WOT.

I hope to apply this setup in the next week or so.