External PCV too much vacuum?

Stevo585

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Dec 16, 2022
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Here is the setup -

Head ports are plugged.

I have the VTT valve cover with a -8 line into catch-can then out of catch-can to a check valve flowing into a -8 on the intake manifold.

The car is pulling tremendous amounts of vacuum that the car won't idle without the oil cap off (which makes sense because the system is closed) When the oil cap is off I still measured 25hg of vac at idle.
I also have the VTT vac relief fitting that does not seem to do anything.

What is the best way for me to get vac relief? I thought about getting the VTT crank case breather and taking out the ball to just have a filtered vac relief, are there any other options?
Do I replace my check valve with a PCV valve to limit the amount of vac?
 

Stevo585

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Dec 16, 2022
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@KnighTT I just read your thread - Please chime in with your thoughts.

My high-side also has a check valve. With the closed system I need a way to vac relief and my VVT vac relief fitting is not giving enough relief / even working.
 

steve30

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Sep 26, 2019
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I think your low side hose size is too big and you should be using the oem flapper on the high side. I just finished my external pcv setup and I'm not experiencing any issues. Also make sure the valve for the low side is an actual PCV valve and not just a simple one way check valve.
 
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BEAT_ITN54

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Aug 25, 2022
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After several diffrent diameters I ended up using 5/16 as the vaccum source. I imagine your pulling too much that the relief valve cant keep up. I'm using a cheap brass valve and its fine.
 
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ShocknAwe

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I think I'm using 3/8" with vac off the TB. Wasn't pulling vacuum in my crankcase recently so deleted my flapper rather than buy a new one and using the aforementioned vac relief following instructions from Martymil and it works fine.

Low side Routing: VC with PCV delete -> 2jz valve -> catch can -> check valve -> TB
 

Stevo585

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Dec 16, 2022
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@ShocknAwe @martymil Yeah I am going to step down my low side hose size. Do I just need a stock 2jz pc valve?

Also is the OEM high side flapper acutally metered? it looks like a simple 1 way valve as there is no resistance/spring on the "door/flapper" it's either open or closed for vac or boost.
 
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ShocknAwe

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@ShocknAwe @martymil Yeah I am going to step down my low side hose size. Do I just need a stock 2jz pc valve?

Also is the OEM high side flapper acutally metered? it looks like a simple 1 way valve as there is no resistance/spring on the "door/flapper" it's either open or closed for vac or boost.

There's a small hole in the flapper door.

Yes I'd just get a stock 2jz valve. But I'm a believer in the stock VC so grain of salt we don't have the same hardware.
 
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martymil

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If you use a vtt valve in the high side you need a vacuum relief valve in the valve cover otherwise use the oem flapper.

in the low side use a valve like this or similar that will sort you out.

20230521_153917.jpg
 

Stevo585

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Dec 16, 2022
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@martymil this is going to be my new setup:
VVT valve cover

Lowside: 8an into catch can -> 8an out catch can -> 2jz PCV valve (mounted vertical) -> one way check valve -> Intake manifold
Highside: Flapper into catch can -> out catch can VTA

If the vac is still to much I'll run the same set up and just step the hose sizing down.

I'm not sure if I have an older VTT VC but the 3rd port where a vac relief would go is on the right side front of the VC, with the vac relief valve on I can't close the hood...

Side note I hate the look of hose clamps - without the hood closing I'm stuck using the flapper valve. Could I put the flapper valve on the out of the catch can so I could at least hide the valve in the engine bay and not have it on top of my valve cover? or does it have to be before?
 

BEAT_ITN54

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Aug 25, 2022
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ahhh you just blew my mind. Did not even think of that.

is it the same thread pitch?
No it's not. I used a 90° fitting to 3/8 hose that runs the valve out of the way with a small filter. Don't remember the size. I think a post was made. Look for service port on head
 

ShocknAwe

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On the front head service port.
 
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Dumaurier7

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I think most people go with 8AN or larger lines which are too big (in my opinion) for the system. I recently did my install using Radium cans, VTT VC fitting, VTT mini check ,6AN hoses on the low side and 10AN on the high side with the OEM flapper valve. With the engine idling and the dipstick removed from the low side can removed there is a very strong vacuum (in the can) which suggests that the vacuum pull is more than enough to evacuate the crankcase during low load conditions. To date I have not gotten a single code nor drop of oil in the system.
 
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