Catch Can Idea

Mike GMC · March 30, 2019

I know, another catch can thread, but bear with me for a moment. I had an idea and I don't know if it would work or if it's just dumb. It relates to the CSS. I was thinking, it might work to put check valves in the factory lines from the air intake to the valve covers instead of bridging the vale covers and using the oil fill to connect to the air intake. It would force all the air leaving the block to go through the PCV and through the can while allowing only intake from the valve covers. Is this dumb or does it have any merit?

TXGREEK · March 30, 2019

Interesting, hey SS502 what are your thoughts on this idea?

Sent from above

SS502 · March 31, 2019

On ‎3‎/‎30‎/‎2019 at 1:07 PM, Mike GMC said:

I know, another catch can thread, but bear with me for a moment. I had an idea and I don't know if it would work or if it's just dumb. It relates to the CSS. I was thinking, it might work to put check valves in the factory lines from the air intake to the valve covers instead of bridging the vale covers and using the oil fill to connect to the air intake. It would force all the air leaving the block to go through the PCV and through the can while allowing only intake from the valve covers. Is this dumb or does it have any merit?

Are you saying putting one way check valves on each line (the two lines that go from the valve covers to the stock air box) effectively not allowing any airflow INTO the air box from the valve covers? I am probably not seeing in my mind what you’re trying to say. If you’re suggesting that then I would say no AND IT’S NOT dumb to ask or think outside the box. My take on it is this:

If you capped both valve covers or put check valves on the stock lines you would probably blow gaskets or seals. Valve covers vent pressure at WOT. This would probably be ok if you made your pcv 3/4” ID like the diesels do.. then you could probably do that without issues but GM uses a 5/16 pcv line...at idle the manifold vacuum will pull 17 or more and at a light cruise say 1500 rpm even more vacuum.. when that happens it evacuates the pcv pulling a vacuum on the crankcase.. which in turn pulls fresh air into the valve covers. This is good.. fresh air comes in and flushes the bad crankcase windage vapor out the pcv. Now when you floor it.. manifold vacuum drops to practically nothing.. crankcase pressure builds and vents all the pressure out the valve covers. Just an FYI, I run a dual setup that uses a mini can vs a CSS but does basically the same thing but instead of allowing that tiny bit of oil trapped by the CSS to return, it collects in the mini can...since we don’t run WOT all the time my mini can would/will take a very, very long time to accumulate oil. What it does allow is unimpeded access to the oil fill and dipstick. In other words, I don’t have to add oil through a CSS (if it has that disconnect capability) or remove it. You can see that I really don’t have anything in the way.

Edited April 1, 2019 by SS502
Changed the font to a normal size...

SS502 · March 31, 2019

...and on that I will remove myself from Catch Can discussions, too many people get defensive on the issue and it’s really all a personal choice.

BigBlueLB756 · March 31, 2019

But you're right.

Mike GMC · March 31, 2019

Thanks, those are we good reasons NOT to do what I was thinking.

KARNUT · March 31, 2019

Not to throw a wrench in the catch can debate. You would think if GM could convince people to do an injection flush every 30K ( if you use top tier gas it’s not needed), they could convince people to do an induction treatment every so many miles to clean intake valves.

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BigBlueLB756 · March 31, 2019

They probably don't want you to do it. The service department will do a much better job.

Or not.

KARNUT · March 31, 2019

They probably don't want you to do it. The service department will do a much better job.

Or not.

Of course the service department, there’re always trying to up sell. I never had injection cleaning done. Every thirty thousand miles they try to sell me one.

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Paintor · April 1, 2019

This is what men do.

BigBlueLB756 · April 1, 2019

Maybe "little" men.

SS502 · April 1, 2019

5 hours ago, Paintor said:

This is what men do.

April fools joke?

Doublebase · April 6, 2019

Kind of interesting...I always was taught that the valve cover vents were necessary for removal of crank blowby fumes. But it makes sense that during WOT intake manifold drops to the point that you're not pulling through the PCV, yet pressure in the crankcase pushes it out through those valve cover vents.

Explains why ive sometimes seen oil tracking into the throttle body, and up through the air snorkel and those vent lines on some cars. Good info.

As for a catch can, yeah I run one. I empty it every 2,000 miles or so and it's usually pretty full (mix of oil water). I might send a scope down my intake and take a look at the valves - truck has 27,000 miles now - I've run two cleaners into the manifold since new and installed the catch can at around 12,000 miles. Interested to see how those valves look now.

Edited April 6, 2019 by Doublebase

Paintor · April 9, 2019

Your PCV valve SUCKS crankcase gasses into the intake.

Your valve covers hoses by EPA and Patent ...are supposed to provide fresh air in.

You boys getting OIL comin out yer valve cover hoses into the intake....would imply General Motors PCV Emission Control is a ....faulty.

Yer truck will retard timing when it is sensing KNOCK (from burning oil) and give you even worse emissions...mpg.

But of course none of you will admit in 1,000 years GM’s PCV system is faulty and will buy catch cans to try and keep yer truck from retarding timing from knock as she chokes down ZERO WEIGHT OIL. Good luck with that.

Edited April 9, 2019 by Paintor

BigBlueLB756 · April 9, 2019

Doublebase is correct; Paintor has errors in his thinking concerning the function of various parts of the PCV system.

The PCV valve/port "allows" crankcase pressure and possible blow-by an exit medium from the engine to be drawn into the intake plenum by intake vacuum through the driver's side valve cover hose. The passenger's side valve cover hose is a path for any air needed to replace that pressure. That's why, on a boosted engine, check valves are inserted into these lines to prevent excess pressure created by the boost system from possibly damaging engine seals.

Snot in the catch can proves there is something that needs correcting in the design. We're just trying to keep things "clean".

You do use a handkerchief, don't you?