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Help with PCV for turbo setup

94GrandPrixSE

94GrandPrixSE

New member
I have read everything I could find on how to make the pcv functional instead of breathers I'm sort of lost and was hoping someone could verify what I'm thinking is right before I start drilling and tapping. Engine is l67 with l67 heads, NA intake manifold. Can I block off the stock pcv on top the manifold and run a hose from the rear valve cover to catch can to check valve to a vacuum source. On the front valve cover run a hose to intake on turbo? (Where this is little to no vacuum)??

what do you guys think?
 


You'll want to check out my thread here: The PCV Thread

Basically, you'll want to follow my adaption of the catch can install, except which head is which depends on what your upper intake manifold is (basically just read all of it). You'll want the catch can I mentioned, as well as one off the intake. If your intake is internal (L67) you'll want to block this off and either modify oil cap or drill a point for your intake.

*IMPORTANT* if you don't add baffling under the cap or point you tapped, you WILL suck oil. There's good universal baffles you can install.

The breather port needs to go before turbo, and the vacuum port (see Catch can install) needs to have a one way check valve pointed towards vacuum (this is to prevent positive crankcase pressure when turbo is at high boost).

There's many ways you can do this, but the dual catch can system I described is hands down the most effective and the cleanest turbo setup possible.

Good luck!
 
Important note, make sure you read the thread thoroughly. Stock L67 your intake is the front head, with L37 or L26 intake manifold, your intake head is actually the rear one. (I know, why gm?) Even the all data diagram has it listed wrong!

If you tap the wrong head, your pcv will not function correctly, if at all.
 
I read your write up a few times ton of info great post thank you! I mostly understand what I have to do but I don't understand the point of an catch can on the intake side. I apologize for my lack of understanding here haven't had much experience with pcv systems because I haven't need to yet. Also I do not understand if I could just run hoses off my valve covers instead of going through the UIM. I could make a cleaner looking setup if It would work and should eliminate designated sides to use for intake and dirty side?
 
94GrandPrixSE said:
I read your write up a few times ton of info great post thank you! I mostly understand what I have to do but I don't understand the point of an catch can on the intake side. I apologize for my lack of understanding here haven't had much experience with pcv systems because I haven't need to yet. Also I do not understand if I could just run hoses off my valve covers instead of going through the UIM. I could make a cleaner looking setup if It would work and should eliminate designated sides to use for intake and dirty side?
Click to expand...

You are correct. If you run your own setup external you wouldn't have to worry about the heads, but you would need to tap both heads. The air intake catch can is to catch any stray oil or moisture from the turbo or if the system reverses. Basically, during high boost, the regular vacuum side of the loop completely closes off (check valve) to prevent the crankcase pressurizing, but the engine is still producing positive crankcase pressure. So the pressure causes the loop to "reverse" and the intake becomes like the vacuum side and vents crankcase pressure to before the turbo, so without the catch can there, all the vapor and oil mixture will spray onto your turbo. Again, this only happens during high boost so it isn't much, but personally, I wouldn't want to spray that into my turbo.... it's up to you.

If you route everything external (which is actually what I'm planning on doing), you need to install baffles to make sure the oil doesn't get sucked up or clog the lines with buildup and you'd have to do BOTH. Then you'd have to drill and tap where the old pcv valve went and run one external. The tricky part is that the pcv valve is actually designed for the flow rate of our engine, so the only universal one that will work would be this one: Dual Flow Adjustable PCV Valve – M/E Wagner Performance Products. Your other option is to somehow create an inline "holder", or find a way to adapt a grommet like off a sbc. Most of the sbc used a similar pcv valve that just uses a grommet in the valve cover to hold the pcv valve. The latter option would be the most practical.

With both options though, you will either have to find a place on the valve cover that has enough clearance for the lifters both for the pcv valve and the baffle, or you'll have to have custom valve covers made, or you'll have to pick up another valve cover with oil filter hole and find a way to add baffling under it and install the grommet for your pcv valve and hose.

Obviously you'll have to remove both valve covers, drill the holes for the pcv, install the pcv valve in one of the valve covers as mentioned, then route the pcv one to a catch can, then to a source of vacuum, and the other one either directly before the turbo, or to another catch can then to before the turbo.

Oh, and do NOT forget the one way check valve after the pcv valve side catch can going to the vacuum. The pcv valve does a good job at stopping backfires, but not so good at completely closing with boost, so without it, boost will leak past and pressurize the crankcase and cause issues.
 
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And remember, when looking for a catch can, you're looking for a "closed loop" not an "open loop" with a breather on it. It must be able to function under vacuum without leaking (or you'll have a vacuum leak). Mishimoto makes good ones but they're very pricey.

The one I referenced in my pcv thread I've had installed without issues for several months and works quite well. Plus, it's dirt cheap.
 


94GrandPrixSE said:
with the check valve you really wouldn't leak boost tho right? So would you still need a better pcv valve?
Click to expand...

Basically the pcv valve isn't designed for boost. You get around that by adding the check valve to the pcv valve. The reason you place the check valve after the catch can is so that it doesn't get clogged with oil. There really isn't a need to get a new pcv valve.
 


If you're re-routing both front and rear, the position doesn't matter. The only thing that matters is that one head is your fresh air intake and has the first catch can going to intake before the turbo, no check valve or pcv valve; then the opposite head is your crankcase exhaust that first goes through the pcv valve, then the second catch can, then a one way check valve, then to a source of vacuum. This setup covers all stages of pressure and keep the crankcase from being pressurized even under high boost and keeps oil out of your intake in all scenarios. Hopefully this makes a bit of sense. Here's a diagram I found that shows the setup (this is not my image, I just found it on google)

pcv_2ls1extfi.jpg
 
Ok thanks for the reply. Could I tap the old pcv location (vacuum is blocked) and use that instead of my front valve cover? And route that through my catch can and then to my air filter before turbo? Using series 3 upper and lower intake.
 
94GrandPrixSE said:
Ok thanks for the reply. Could I tap the old pcv location (vacuum is blocked) and use that instead of my front valve cover? And route that through my catch can and then to my air filter before turbo? Using series 3 upper and lower intake.
Click to expand...

nononononononon don't do that! The heads and routing has to be on separate heads. Since you have the L26 upper, your intake head isn't your front head like L67, it's your rear head. Your front head is actually the exhaust route. You can keep your stock location just fine for your pcv and just re-route the map sensor like I did and plug the little hole inside that goes to vacuum and route an elbow out the original map sensor location and route that to your catch can to your check valve to vacuum. Using that, your options for the intake are to either to tap the rear valve cover and bring that to before your turbo, or to tap into the stock intake location and route that through a catch can to before your turbo intake. If you have L36 plastic intake, you'll have to plug the stock pcv intake at either where the throttle body attaches to the manifold and drill and tap somehow into the internal routing to bypass, or if you're using the L26 aluminum upper, all you have to do is bring the stovepipe intake hose out to before your turbo intake. Aluminum intake is really the way to go here. That being said, again, you can tap the rear head for air intake, just make sure you have baffling and check your valve clearance!
 
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