Catch Can -- AOS/PCV System Installation

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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
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That amount of oil after one day... leads me to believe it's got some serious blow-by issues. Just a guess, based on the fact that several early 2010's GMC/Chevy V8s with AFM screwed up the rings which leads to excessive blow-by. Later PCV systems, I think past 2003 or so, started using fixed orifice PCV, which technically should be changed to PCO, positive crankcase orifice. An engineered leak of sorts.

Catch cans are almost a common installation for a lot of LS engine folks for sure. I have one on the 2010 and 2013 Camaros. I get negligible oil caught, but it does work. When I upgraded my throttle body on the 2010, the intake floor was dry. On the flip side, I know of others that get a bottle capful or two between oil changes. My oil changes are once per year instead of mileage anyway. Do cans help? Most people think so. They certainly do not hurt if a quality unit is installed correctly. It's usually helpful to keep the intake clean and not have the oil gob up the valves. It simply acts as an in-line separator. Difference is you'd either burn that oil, or catch it in the can. One way or the other.
 
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L92 OLDS

Comic Book Super Hero
Mar 30, 2012
2,642
113
West Michigan
I put one on my wife's hot rod Lincoln as a precaution. Running a catch can and using synthetic oil are a good ideas for any modern direct injection engine.

Front.jpg
 

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81cutlass

Comic Book Super Hero
Feb 16, 2009
3,524
113
Western MN
Clean install!

It seems like there are two schools of thought on these systems. Your method (vented can) with minimal vacuum, with a 'clean' air supply of ~1 inch of vacuum supplying suction to one side of the can and dirty crank air supply to the other can port. Other method is the closed, unvented high vacuum setup where the catch can is literally just a filter in the normal PCV circuit.

Do you know if there is some trick valving on your catch can? I see a lot of vented setups like what you have, but I don't understand how they functionally create any vacuum on the crank case like a traditional PCV system. It seems like the filter on the can is just creating a path of least resistance so any vacuum created from inside the air cleaner is just going to route through the catch can filter and never put any vacuum on the crankcase. I just don't see any benefit from routing the suction line to the air cleaner when there is a vent on the can is what I am getting at. Maybe they all have a special valve inside to shut the filter off unless there is positive can pressure that I am not aware of.
 
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Tony1968

Royal Smart Person
Jul 1, 2018
1,445
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NW Indiana
Clean install!

It seems like there are two schools of thought on these systems. Your method (vented can) with minimal vacuum, with a 'clean' air supply of ~1 inch of vacuum supplying suction to one side of the can and dirty crank air supply to the other can port. Other method is the closed, unvented high vacuum setup where the catch can is literally just a filter in the normal PCV circuit.

Do you know if there is some trick valving on your catch can? I see a lot of vented setups like what you have, but I don't understand how they functionally create any vacuum on the crank case like a traditional PCV system. It seems like the filter on the can is just creating a path of least resistance so any vacuum created from inside the air cleaner is just going to route through the catch can filter and never put any vacuum on the crankcase. I just don't see any benefit from routing the suction line to the air cleaner when there is a vent on the can is what I am getting at. Maybe they all have a special valve inside to shut the filter off unless there is positive can pressure that I am not aware of.
In agreement here. Unless some type of check valve is used it wouldn't work properly.
 

Kiko

Master Mechanic
Thread starter
Apr 14, 2009
287
63
Ottawa, Canada
Clean install!
...
Do you know if there is some trick valving on your catch can? I see a lot of vented setups like what you have, but I don't understand how they functionally create any vacuum on the crank case like a traditional PCV system. It seems like the filter on the can is just creating a path of least resistance so any vacuum created from inside the air cleaner is just going to route through the catch can filter and never put any vacuum on the crankcase. I just don't see any benefit from routing the suction line to the air cleaner when there is a vent on the can is what I am getting at. Maybe they all have a special valve inside to shut the filter off unless there is positive can pressure that I am not aware of.

First of all -- thanks! Now, to answer your question: The catch can has a PCV valve on one port and hooks up to the intake manifold from the other port. Fresh, filtered air gets sucked in via plumbing on passenger side valve cover.

FWIW, this was all new to me when I started, so for anyone else out there that needs info, i've attached a good document to read.
 

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Supercharged111

Royal Smart Person
Oct 25, 2019
2,433
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Colorado Springs, CO
First of all -- thanks! Now, to answer your question: The catch can has a PCV valve on one port and hooks up to the intake manifold from the other port. Fresh, filtered air gets sucked in via plumbing on passenger side valve cover.

FWIW, this was all new to me when I started, so for anyone else out there that needs info, i've attached a good document to read.

So the PCV is in the small line leading to the can from the intake manifold? Since the can has its own filter, it won't pull any fumes out of the crankcase via the breather in the air filter. The can should be sealed and installed inline on the side leading to the air filter. The PCV should just lead from the intake manifold to the valve cover. Unless I'm misunderstanding your setup?
 

Kiko

Master Mechanic
Thread starter
Apr 14, 2009
287
63
Ottawa, Canada
So the PCV is in the small line leading to the can from the intake manifold? Since the can has its own filter, it won't pull any fumes out of the crankcase via the breather in the air filter. The can should be sealed and installed inline on the side leading to the air filter. The PCV should just lead from the intake manifold to the valve cover. Unless I'm misunderstanding your setup?

No, the PCV is on the catch can -- hose from driver valve cover connects to catch can, which has the PCV built in. The other side of the catch can is connected to the intake manifold. The manifold, which operates under vacuum due to the pistons drawing air/fuel mixture via the carb, also pulls dirty air from the engine via the PCV and catch can. The can itself is filled with a small mesh so any oil droplets can attach themselves (remain in the catch can) and not flow further via the air stream into the intake. The catch can also has a restrictive filter on top to aid in the scavenging process. There is a really good explanation of this process in the document I attached previously.
 

81cutlass

Comic Book Super Hero
Feb 16, 2009
3,524
113
Western MN
First of all -- thanks! Now, to answer your question: The catch can has a PCV valve on one port and hooks up to the intake manifold from the other port. Fresh, filtered air gets sucked in via plumbing on passenger side valve cover.

FWIW, this was all new to me when I started, so for anyone else out there that needs info, i've attached a good document to read.

Thanks for answering the question by the way, don't mean to criticize. I just see a lot of these vented systems and never understood how they worked. Most places just say "they are great!" and provide no explanation of routing.

Personally I have a closed, unvented system on my LS where the valve cover port routes to a catch can full of steel wool which dumps into the bottom and I have a suction line in the top that extends about half way into the can with a number of small holes drilled in the side which then feeds to the plenum above my blower. I also have a PCV valve in line b/w the can and the vacuum source at the plenum.

It get about 1/4 cup of gooey oil/water every oil change on my unknown mile stock bottom end 6.0, so it works.
 
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Supercharged111

Royal Smart Person
Oct 25, 2019
2,433
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Colorado Springs, CO
No, the PCV is on the catch can -- hose from driver valve cover connects to catch can, which has the PCV built in. The other side of the catch can is connected to the intake manifold. The manifold, which operates under vacuum due to the pistons drawing air/fuel mixture via the carb, also pulls dirty air from the engine via the PCV and catch can. The can itself is filled with a small mesh so any oil droplets can attach themselves (remain in the catch can) and not flow further via the air stream into the intake. The catch can also has a restrictive filter on top to aid in the scavenging process. There is a really good explanation of this process in the document I attached previously.

I understand how a PCV/breather setup works and yours is a bit different. I've always seen the PCV subject to vacuum and with the filter on the can I don't see how it's possible on your setup. I'm sticking to my guns here, no doubt the blowby is being filtered but the ability of the engine to draw in its own crankcase fumes remains in question for me. With the filter on the can, the engine will draw filtered air from it and not the passenger VC/air cleaner.
 

Kiko

Master Mechanic
Thread starter
Apr 14, 2009
287
63
Ottawa, Canada
I understand how a PCV/breather setup works and yours is a bit different. I've always seen the PCV subject to vacuum and with the filter on the can I don't see how it's possible on your setup. I'm sticking to my guns here, no doubt the blowby is being filtered but the ability of the engine to draw in its own crankcase fumes remains in question for me. With the filter on the can, the engine will draw filtered air from it and not the passenger VC/air cleaner.

Sorry for not getting back sooner. I can definitely understand the confusion that the filter on top of the catch can creates. There's a check valve and that filter is only "one way" -- i.e., closed by vacuum and open only for pressure release. Hope that helps explain the setup.
 
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