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Old 10-22-2022, 01:25 AM   #1
StiLimited
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Default Rerouting the crankcase/valve cover venting system, need help

6. The OEM PCV and crankcase venting system seems way over complicated. Why do they put 2 vent ports on each valve cover and right next to each other? I see the crankcase vent and it then goes UP and over and then back down to the valve cover vents. Why? Why not just run straight lines to the valve covers? Again seems overly complicated to me and make it more complicated than it needs to be, unless there is some technical reason they do that. I will be installing my own AOS and just want to run the rear vents on each valve cover and the crankcase vent to the input of the AOS and cap off those other vents in the valve covers. Can I do that? And what about the PCV valve? Where/why is that there? How is where it's drawing from different from that large crankcase vent? I must be missing something here.
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Old 10-22-2022, 09:09 AM   #2
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IIR one of the ports on each valve cover has a simple oil baffle and the other is open to the top of the head. The open port is to equalize pressure between the two valve covers (not sure how important that is). You should be able to determine which is which by the hose routing. Maybe someone with a set of valve covers off their motor can elaborate. There's some really smart members here with their own theories on how the PCV system should be routed. If you're not in a rush you can wait for them to chime in.
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Old 10-22-2022, 09:12 AM   #3
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Speed density or MAF? If SD run that shot through a large catch can and then overboard.
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Old 10-22-2022, 10:56 AM   #4
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This video by Flatirons Tuning explains it the best with visuals:

https://youtu.be/mO9mxDUDUDc
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Old 10-22-2022, 04:47 PM   #5
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Quote:
Originally Posted by benflynn View Post
Speed density or MAF? If SD run that shot through a large catch can and then overboard.
Just curious but what does that have to do with it? Oh, you are saying if I'm doing SD we can vent outside the engine, right? Don't have to worry about "containing" the air?

Thank you.
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Old 10-22-2022, 04:57 PM   #6
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Don't block any of the ports.

The large ones are the crankcase balance ports and the smaller ones are PCV.

The PCV Valve is either on the back side of the manifold, or in the plastic adapter on the rear breather port tee (depending on what year engine). Some AOS units (like ours) remove the PCV valve, some do not.
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Old 10-22-2022, 04:58 PM   #7
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delete double post
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Old 10-22-2022, 05:45 PM   #8
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Quote:
Originally Posted by a5m View Post
This video by Flatirons Tuning explains it the best with visuals:

https://youtu.be/mO9mxDUDUDc

Yes, I had viewed that before, but watched it again. And I"m glad I did because at the end it suggested this video:


Which was amazingly helpful. Really helped explain the whole situation. Those guys at Flat Irons are really good. Thank you your reply, indirectly it answered my questions. ;-)
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Old 10-22-2022, 07:04 PM   #9
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Quote:
Originally Posted by KillerBMotorsport View Post
Don't block any of the ports.

The large ones are the crankcase balance ports and the smaller ones are PCV.

The PCV Valve is either on the back side of the manifold, or in the plastic adapter on the rear breather port tee (depending on what year engine). Some AOS units (like ours) remove the PCV valve, some do not.
Got it. So the issue is we are building crankcase pressure, using the turbo inlet (or manifold vacuum) to remove it, but in doing so we suck up oil and need to separate that oil from the intake. Which is a really hard job to do. My intake is always full of oil even on a mostly stock engine. I don't like burning oil. :-) I want that intake to be as clean as a whistle. Oil in the IC kills efficiency. Thank you.
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Old 10-22-2022, 08:32 PM   #10
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Quote:
Originally Posted by StiLimited View Post
we are building crankcase pressure, using the turbo inlet (or manifold vacuum) to remove it, but in doing so we suck up oil and need to separate that oil from the intake.
This sounds like you have an engine health issue that no AOS is going to solve for you. You should not be building any crankcase pressure pulling vacuum from the turbo inlet, and if you are sucking up lots of oil (through an AOS), that's another indication there's an engine health issue.

I would recommend a compression and leak-down test before going any further.
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Old 10-22-2022, 11:27 PM   #11
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Quote:
Originally Posted by KillerBMotorsport View Post
This sounds like you have an engine health issue that no AOS is going to solve for you. You should not be building any crankcase pressure pulling vacuum from the turbo inlet, and if you are sucking up lots of oil (through an AOS), that's another indication there's an engine health issue.

I would recommend a compression and leak-down test before going any further.
No, it's a brand new engine. Rings may not be fully seated but even with the original engine totally stock, whenever I pulled the TMIC there was always oil in it. Not cups, but enough to cause a small puddle where I set it up on end.
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Old 10-23-2022, 12:27 AM   #12
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Quote:
Originally Posted by StiLimited View Post
Yes, I had viewed that before, but watched it again. And I"m glad I did because at the end it suggested this video:

An In depth look at what Crankcase Pressure can tell us on a Turbo Subaru Engine. - YouTube

Which was amazingly helpful. Really helped explain the whole situation. Those guys at Flat Irons are really good. Thank you your reply, indirectly it answered my questions. ;-)
Yes I've come across that one but never watched it because the other one mostly went over my head lol. Yea love their content. They know what they're doing. I should probably watch it to make sense of Subaru's setup.

Glad I could help though

Btw my TMIC always has a light coating of oil, most of it collecting around the gasket on the turbo outlet. Perhaps something isn't exactly right or could be improved with your setup.

Last edited by a5m; 10-23-2022 at 12:33 AM.
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Old 10-23-2022, 01:47 AM   #13
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Well I have a beast of an AOS. It's for a diesel engine. I'm going to try it. It has 1" inputs. :-)
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