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2006 Red Jewel AWD
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Discussion Starter · #1 · (Edited)
I figured i'd post this over here and hope that some of the better tech people and/or GM techs would be able to help with this...I am just having a few issues with the plumbing as my AOS is configured...

As most of you know, I decided that a simple catch can wasn't the best option for relieving PCV system issues that cause our engine to push oil into the intake. I decided to give the Crawford Performance Air-Oil Separator a try. Basically a fancy little unit that uses in an internal centrifuge to separate the oil out and automatically drain it back into the crankcase and feed the clean air back into the engine.

What I need help with is the theory behind how the PCV system works and how I can make the Crawford AOS function properly. As the photo I found in the interwebz below shows, the vehicles equipped with a car intake manifold/throttle body are plumbed as described...


The only difference with the truck intake manifolds is that the port labeled in black as "Blank" is fed to the intake and the port in the LS6 valley cover labeled in the photos as "stale air out" is actually capped off.

What I need to know is, can I change the PCV system's direction of ventilation in any way?

The way the crawford AOS works is in the photo below. Basically, the dirty air/oil feeds from the engine to the (2) side ports on the AOS marked with the red arrows. The centrifuged/separated oil returns via gravity and vacuum into the crankcase from the bottom port on the AOS marked with a green arrow. The clean air after being separated from the oil is returned to the engine through the top port on the AOS marked with the black arrow.


My question is this, how do you see making the connections so all of the ports are connected properly so the AOS will function as it should?
 

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2006 Red Jewel AWD
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Discussion Starter · #2 ·
The way I connected it had me baffled until I realized I had made one simple mistake. I plumbed the air return into the intake manifold, which is apparently bad because during decel, the intake's huge amount of vacuum will cause the AOS to basically feed oil right into the intake, so I have to now change the air return to a point outside the intake manifold before the throttle body. Other that that, I figured the (2) valve cover ports would work well for the oil/air feed from the crank case into the AOS and the valley cover (being the lowest port readily available) would be perfect for the oil drain back into the crankcase. The only issue here is the fixed orifices that will limit the amount of oil the AOS can effectively drain back into the crankcase. So I am thinking I will have to drill and weld a fitting into the valley cover or even the front timing cover to work as an oil drain (similar to a turbo return line). Any thoughts?
 

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'08 TrailblazerSS
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OK Steve, I've given it some thought. If you want the ultimate system to keep oil out of the intake, the solution is to use a puke tank with either an electric vacuum pump or mechanical vacuum pump. That way the suction is not refrenced to the intake at all so no chance of getting oil in there. But, vacuum pumps are very expensive and is another item to wear out in short order, so I understand why you are looking to go this route for a more high mileage street friendly setup.

A few questions first. What are you using as a oriface / restrictor to the "stale air out" ports? This on your engine (boosted)?
 

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2006 Red Jewel AWD
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Discussion Starter · #4 ·
Everything in my PCV system is stock. The Valley Cover is stock and unmodified, the valve covers are stock and unmodified. The only change is that I replaced the oil fill cap with a K&N filter.

Yes, this is on my Procharged LS2...
 

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'08 TrailblazerSS
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I know this was a generic pic pulled off the interwebz but I have to make the joke of good luck finding a 1/2 square port and 1/2 cathedral port intake manifold to fit that engine :bum::biggrin2:
 

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2006 Red Jewel AWD
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Discussion Starter · #6 ·
I know this was a generic pic pulled off the interwebz but I have to make the joke of good luck finding a 1/2 square port and 1/2 cathedral port intake manifold to fit that engine :bum::biggrin2:
I noticed that as well...thought it was funny!
 

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Everything in my PCV system is stock. The Valley Cover is stock and unmodified, the valve covers are stock and unmodified. The only change is that I replaced the oil fill cap with a K&N filter.

Yes, this is on my Procharged LS2...
I'm having trouble seeing how this AOS will work in a boosted application without modification. You'd have to put a check valve on the top port of the can to block boost (+ manifold pressure). You'll also need metered orifaces for both the side ports on the can. That will keep the vacuum from running away (spiking) on you when you lift after a hard pass where the vacuum is the highest on sudden engine decel.

The can won't work if you don't have a vacuum refrence. If you plumb the top port of the can pre throttle body and procharger, there is no vacuum present at idle, therefore it wont work. You may get a little vacuum at higher RPMs due to venturi effect but not enough to scavange vapors and moisture IMHO. Plus you'll be running dirty oil vapor and moisture though the procharger.
 

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Some PCM of NC bolton's
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How about this Steve both valve covers to red arrows on can black arrow to pre blower between af and blower (always -psi even greater when @wot) and bottom of can to valley cover (only if can is higher than port so oil will drain back into the engine)
 

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OK now on to port discussion. On the LS6 like in the pic above they moved the PCV vapor pickup to the valley cover from the valve cover. Why? Well the valley cover has the least amount of chance to pick up liquid oil under severe cornering conditions and since that cavity doesn't see anything but splash lube from the crank and cam, there isn't much liquid oil to be picked up at that point. With the pickup at the rear of the driver side valve cover, there is a better chance of picking up liquid oil under vaccum for accelerating and cornering. There are buit in baffles in the valve covers but they dont work all that great or we wouldn't need a catch can at all.

That pickup point in the LS6 valley pan utilized a oriface built into the tube that connected to that port. So if you use that port to extract vapor, it needs to be restricted with an external oriface.

If you look at the pickup port on the rear of the driver side valve cover in your stock LS2 you will see the oriface there. On the LS6 the port at the rear of the driver side valve cover is blocked off as you mentioned because they used the valley port instead.

The oil drainback port like you mentioned has to be down below where the can is mounted for gravity feedback to the pan. Looks like you may have to fab something there.

Why not use the LS6 valley cover and driver side valve cover (blocked off port), cap one of the inlet ports of the can, plumb the other inlet port to the valley cover port, refrence the top vacuum port of the can to the intake manifold with a bad ass high quality check valve in place, and fab up an oil drain back. I don't see the need for multiple vapor pickups to be used on the engine. Whats the point? To me you are doubling the chance of picking up oil.
 

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2006 Red Jewel AWD
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Discussion Starter · #11 ·
I'm having trouble seeing how this AOS will work in a boosted application without modification. You'd have to put a check valve on the top port of the can to block boost (+ manifold pressure). You'll also need metered orifaces for both the side ports on the can. That will keep the vacuum from running away (spiking) on you when you lift after a hard pass where the vacuum is the highest on sudden engine decel.

The can won't work if you don't have a vacuum refrence. If you plumb the top port of the can pre throttle body and procharger, there is no vacuum present at idle, therefore it wont work. You may get a little vacuum at higher RPMs due to venturi effect but not enough to scavange vapors and moisture IMHO. Plus you'll be running dirty oil vapor and moisture though the procharger.
The thing is, this AOS is designed to work specifically with force induction Subaru applications as it sits. No modification needed. The metered orifices you are saying need to be used are already part of the LS2 valve covers and LS6 valley cover on the engine now. My main concern is how the PCS system is designed to "flow" so I can plumb the AOS to match the PCV flow already designed into the engine.

Basically, as designed, the LS2 works like this (as I understand):

The passenger valve cover is where fresh filtered air is fed into the passenger valve cover and cycled down through the rockers and through the pushrod ports and down into the manifold valley. At that point, the condensation and oily air is cycled as follows:

Car manifolds - The port on the valley cover is fitted with a hose that feeds into the intake manifold just behind the throttle body. The port on the driver valve cover is capped off.

Truck manifolds - The port on the driver valve cover is fitted with a hose that feeds into the intake manifold on the very top.The port in the valley cover is capped off.

Knowing this, my feeling is that I can run both the valley cover and the driver side valve cover as the oily air feed into the AOS. Then I can cap the fitting on the passenger side valve cover because I have the K&N filter to bring fresh filtered air into the PCV system.

The clean air return that was plumbed into the intake manifold port (behind the throttle body) was causing too much vacuum draw and actually siphoning oil right into the manifold. So in looking at how it plumbs into the Subaru system (and talking to Quirt @ Crawford) the clean air return needs to be placed in front of the throttle body so the increased vacuum after chopping the throttle will not cause the oil siphoning issue.


How about this Steve both valve covers to red arrows on can black arrow to pre blower between af and blower (always -psi even greater when @wot) and bottom of can to valley cover (only if can is higher than port so oil will drain back into the engine)
That is how I logically thought it should be and how I plumbed it first, but it was wrong...maybe the only thing I did wrong was plumbing the clean air return into the intake, but since the valley cover has a restriction orifice, I can't effectively return the oil through that port in the valley cover.
 

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'08 TrailblazerSS
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Rather than mess with check valves and whatnot, I wonder if this would work on your truck.....

http://www.grimmspeed.com/catalog/product_info.php?cPath=91&products_id=191

It allows you to keep the factory PCV system in place, but still pushes only clean air through the motor.
I think you'll still need a check valve when using this on Steve's setup. Because the subaru PCV has a check valve for boost built in to the stock sytem, Steve's doesn't.

Speaking of which, Steve, what do you have in place now to keep boost pressure from backfeeding into the crankcase with a stock PCV system?
 

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TT AWD TBSS Jeep
TT AWD SS Pwrd Jeep
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If you want to keep it near stock, you will need to move air through the engine and vent it. I did something similar on my GN. I would reroute a bit though. Try this.

1. Take and hook up the red and green ports (stale air out, and fresh air in) to the suction side (middle ports of the unit).

2. For the suction, (sucking clean air only), hook up the Top port of your new device to where ever you have a port that has suction. EX: stock would be the 1/2" port in pipe going to throttle body. If your supercharged, hook to suction side of air inlet on supercharger. But like Jayspeed says, make sure it is clean air coming out of that thing, so your supercharger doesnt get gunked up

3. Route drain to pan as intended

4. Where your last port is, that says blank, you will need some kind of mini K&N breather to let clean air in the engine. This system will work under boost. As the crankcase pressure climbs, the suction side still moves air out via the inlet prior to supercharger. No boost pressure will get into the crankcase this way. If by some wierd chance, the crankcase pressure climbs higher than the suction of inlet of supercharger can take in, the rest will be vented to atmosphere via the mini K&N.

Here is a link to the several differant kinds of mini K&N you will need.

http://motors.shop.ebay.com/i.html?..._sticky=1&_trksid=p4506.c0.m245&_sop=15&_sc=1

Good luck with the system, and write a how to with parts, and costs so others can duplicate your results/efforts.








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Trailblazer SS
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Sorry to run off topic, but its cool to see another GN/TBSS owner in WI. My grandma lives in Germantown lol.
 

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2006 Red Jewel AWD
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Discussion Starter · #16 ·
I think you'll still need a check valve when using this on Steve's setup. Because the subaru PCV has a check valve for boost built in to the stock sytem, Steve's doesn't.

Speaking of which, Steve, what do you have in place now to keep boost pressure from backfeeding into the crankcase with a stock PCV system?
The thing is, both PCV valve and the Check valve are both taken out of the system when you install the AOS on a Subaru...Quirt specifically told me not to run any check valves, just keep the clean air return away from high vacuum areas, like in the intake manifold behind the throttle body...
 

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TT AWD TBSS Jeep
TT AWD SS Pwrd Jeep
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Do you think my routing idea above would work?
 

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2006 Red Jewel AWD
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Discussion Starter · #18 ·
It could have worked, but the LS engines' PCV system is not honestly going to be ideal for using the AOS as designed. Since my system is supergharged, it limits where I can plumb an air return and so on. After speaking with HOB, Andy at A&A Corvette, Crawford as well as a few people on here, we decided to eliminate the whole system and run K&N breathers on each valve cover and call it a day. Not chance of anything going wrong and no chance of any oil making it back into the intake system.
 
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