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Old 05-22-2018, 07:46 PM   #1
PVNRT
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Default Question about keeping boost out of catch can

I just finished a triple catch can install, one dedicated for each head breather and one that intercepts PCV line going directly into the manifold. I was sitting back looking at it all and realized that the PCV can will see boost pressure, I cut the line after the valve and ran it to the can but the can outlet connects straight to the manifold. On a stock setup this works ok because it only pressurizes a small 6" line back to PCV then it is blocked by the PCV. In my situation it will pressurize the whole can.

So I am thinking instead of using a mystery brand Chinese check valve, using an OEM turbo car PCV to prevent can from seeing boost as these are designed to close with boost. I will put it on the line feeding the can and leave the Subaru PCV in factory location, on the block.

I don't want to use another Subaru valve because of the stupid diagnosis port. I am looking for a valve with an in and an out and thats it.

Has anybody used a DSM or other factory car PCV to do what I am doing? I will scour ebay and hopefully find one with 5/16th ports but wanted to know if anybody has found an oem PCV to do what I need with only 2 ports?

Questions comments concerns insults are all welcome.
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Old 05-22-2018, 07:53 PM   #2
PVNRT
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Picture of setup just because...all lines are on now though. Those are basically Mishimoto cans without the label or the markup. 1/2" all the way through with a baffle. Probably overkill to run 3 but it seems ideal.


Last edited by PVNRT; 05-22-2018 at 08:14 PM.
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Old 05-23-2018, 06:18 AM   #3
A-man07
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The PCV closes under boost and keeps boost pressure in the intake manifold. You should not need an additional check valve. Your picture does not explain your routing.
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Old 05-23-2018, 10:15 AM   #4
PVNRT
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Quote:
Originally Posted by A-man07 View Post
The PCV closes under boost and keeps boost pressure in the intake manifold. You should not need an additional check valve. Your picture does not explain your routing.

The picture was just to show where I put them....cheap eye candy it doesn't show the routing.

One can is dedicated to PCV line, from oem PCV valve outlet to intake manifold inlet just that one line. The intake manifold will pressurize the can when in boost so I was looking for a factory turbo car PCV that will seal against boost not just vacuum and just wondering if anyone has found one with similiar size ports that will fit inline.

Goes like this (2004 WRX) Oem PCV valve on block outlet---> catchcan---->directly back to intake manifold. Under boost it flows out of manifold instead of in so I was looking to put a valve there.

Edit: I just realized 2002-2003 wrx pcv doesn't have the diagnostic port so I think that will work it looks like a simple 2 port valve.
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Old 05-23-2018, 11:19 AM   #5
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Google to the rescue...found a corvette forum where they were discussing this same issue. They use a Ford turbo coupe PCV or a turbo Supra PCV inline with the catchcan, they also said you can use a power brake booster check valve. I think I will go with the Ford because it is designed to seal boost, but brake booster check valve should work ok too just gotta keep an eye on it. Just adding this post for future searchers.
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Old 05-23-2018, 03:08 PM   #6
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Ok last update I promise ***128516;.

I just bought a 2002 wrx pcv valve and it turns out it is a direct replacement for the (hollow) brass barb fitting on the back of intake manifold where the original PCV line connects!

That means you can block boost right on the manifold with no chance of boost getting to catch can.

Just make sure you buy a decent quality metal PCV.

Again just posting for future readers this is a great alternative to putting a check valve in the line.
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Old 05-23-2018, 04:18 PM   #7
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The PCV closes under boost so the intake manifold keeps the pressure. If it did not the engine would not see the boost pressure. If there is any chance you are pressurizing your can you don't have it hooked up correctly or you are not understanding the PCV system.
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Old 05-23-2018, 04:53 PM   #8
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Quote:
Originally Posted by A-man07 View Post
The PCV closes under boost so the intake manifold keeps the pressure. If it did not the engine would not see the boost pressure. If there is any chance you are pressurizing your can you don't have it hooked up correctly or you are not understanding the PCV system.
I think the picture alone says that plenty

If you think three cans are good, I'll sell you a kit with four - no one else goes that high so it's gotta be better, right? I'll also sell you an amp that goes up to 11, if you want!
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Old 05-23-2018, 05:27 PM   #9
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I don't think you guys understand what I am doing. There is a can for each valve cover vent, I wanted each valve cover vent to have unrestricted 1/2" venting. Line goes from valve cover vent to can to turbo inlet, two cans are set like that dedicated to vent each side. Disregard PCV for those two cans.

One can intercepts PCV vent line runs to can then returns to intake manifold just like oem. I added the second PCV on intake manifold port because it goes directly to can and would pressurize it when under boost, I left oem PCV in place to work normally. I think what people are missing is the line from can to intake manifold would see pressure without that added PCV. That line also gets pressure with oem setup but its only a small 6" line then it hits PCV and stops....

For some reason PCV routing always starts an argument on here, I will put up pics later, I swear it makes sense.
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Old 05-23-2018, 06:35 PM   #10
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Overall view of 3 cans forgive photo quality its a burner phone and getting dark outside.

Yes 3 cans may be overkill but I wanted to do everyting I can to keep oil out of intake tract, I could have Tee'd valve cover vents together and run 2 cans but then they would have to share a 1/2" line.




Passenger side showing valvecover vent and PCV diagnostic line Tee'd in



Here is where oem pcv line was re routed




Shows where pcv line returns to intake manifold this is where I swapped oem barb fitting for 2002 wrx pcv valve oriented to prevent boost from leaving manifold

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Old 05-23-2018, 06:51 PM   #11
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Just wanted to add I changed over to simple JDM evap solenoid hose routing so that freed up a nipple on the turbo inlet letting each valve cover have its own vacuum source. And yes I junked the windshield washer reservoir to make room I never use it anyways.

Last edited by PVNRT; 05-23-2018 at 06:57 PM.
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Old 05-23-2018, 07:50 PM   #12
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I see what you are talking about, but the thing is... to keep oil out of the intake you only need zero catch cans.

You've probably got 8 lbs of weight in that heavy-ass rubber hose alone right there.

I honestly can't tell if you're trolling or you actually think you need a pile of catch cans under the hood here...

But to answer your question - relocate the PCV between the manifold and can. That means a single PCV. One. Done deal.
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Old 05-23-2018, 08:46 PM   #13
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Quote:
Originally Posted by mrsaturn7085 View Post
I see what you are talking about, but the thing is... to keep oil out of the intake you only need zero catch cans.

You've probably got 8 lbs of weight in that heavy-ass rubber hose alone right there.

I honestly can't tell if you're trolling or you actually think you need a pile of catch cans under the hood here...

But to answer your question - relocate the PCV between the manifold and can. That means a single PCV. One. Done deal.

We can agree to disagree then. The cans were only $25 each and that is money well spent for what they do. And yes this whole thing was a ruse to troll you, you got me. I am a sucker for that legendary NASIOC charm.
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Old 05-24-2018, 06:06 AM   #14
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Quote:
Originally Posted by mrsaturn7085 View Post
But to answer your question - relocate the PCV between the manifold and can. That means a single PCV. One. Done deal.

Listen to mrsaturn if you don't believe me then.

Quote:
Originally Posted by PVNRT View Post
We can agree to disagree then. The cans were only $25 each and that is money well spent for what they do. And yes this whole thing was a ruse to troll you, you got me. I am a sucker for that legendary NASIOC charm.

You agree to disagree on matters of opinion or hypothesis but you are adding complexity to an essentially solved problem. And as to the efficacy of cheapie catch cans, well, you should check after a short time to see if they are actually solving the problem you hope they will. In any case, good luck.
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Old 05-24-2018, 10:06 AM   #15
PVNRT
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After I slept on it you are right it does make more sense to move oem PCV to intake manifold only. When I bought the second valve yesterday I didn't realize at the time it would thread right in to the manifold and replace that nipple, I was about to buy a generic brake booster check valve but decided to get metal PCV and just smooth the threads down and put it inline, I was surprised it fit in the manifold instead.

Its a bit of a mess on the block side where the oem valve is, if I remember right that port on the block is 3/4", I guess I can adapt that to 1/2" and feed back to intake.

I am going to stick with the 3 can setup though, they are good enough quality, I chased the threads and wrapped them all in teflon, the cans do come with o ring seals on all ports also. They have a smaller internal can baffle you can pack with media to help filter also.

When I bought the car, the turbo inlet, compressor housing and intercooler all were coated with a film of oil....the IC had a few ounces trapped inside, guess I am just paranoid about keeping it out now that turbo and inlet are brand new.

I appreciate any help and comments so far, if anything it was worth it to learn that you can just move the oem valve to manifold hopefully it helps somebody in the future. I looked at the oem pcv yesterday and thought that the whole piece including diagnostic port and plastic junction thing as one piece, turns out you can unscrew just the pcv and move that to manifold and just junk the rest of it, replace with a single vent hose instead.

Last edited by PVNRT; 05-24-2018 at 10:30 AM.
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