TECH ARTICLE: PCV system theory and Oil catch cans

[trinydex]

http://forums.evolutionm.net/showthread.php?t=200793


[url=http://forums.evolutionm.net/showthread.php?p=3100326#post3100326]]

I did some research so I could could post on this topic better since it has always bothered me seeing jacked up oil catch can setups. In case people did not know, both the connections that are on the head (PCV and vent) are actally connected too the crank case, not to the air volume in the head itself.

Here is a simple diagram of the stock configuration.

In the stock configuration fresh filtered air enters the crank case through the vent connection and exits through the PCV valve into the intake manifold. This maintains a negative pressure in the crank case and carrys out moisture and any blowby gases thus preventing corrosion and sludge buildup in the crank case.

The PCV valve itself is a check valve (one way valve) to prevent back flow from the intake manifold into the crank case. In a naturally asperated carborated car of the past this check valve prevented any fuel/air mix from entering the crank case, in a modern car it prevents exhaust gases from the EGR system from entering the crank case, and in turbo applications like ours prevents the crank case from being pressurized due to the positive pressure in our intake manifold.

Next post shows how a proper single catch can system needs to be configured.

Keith

http://www.socalevo.net/gallery/albums/userpics/10991/normal_mURI_temp_b5178b0d.jpg


[url=http://forums.evolutionm.net/showthread.php?p=3100326#post3100326]]

With a proper catch can setup, the crank case vent is still connected to the air filter box, then you replace the PCV valve on the head with a simple nipple connected to your catch van via a hose. The PCV valve should be moved to the outlet of the catch can to prevent pressurizing the catch can when under boost. From the catch can a hose goes to the intake manifold like normal.

Since most PCV valves leak on turbo cars we end up with a slight positive pressure in the crank case under boost and this back flows out the vent connection into the air inlet hose leading to the turbo crapping it up with oil, water vapor, and blowby gases. My next diagram is of a dual catch can setup to prevent this.

Keith

http://www.socalevo.net/gallery/albums/userpics/10991/normal_mURI_temp_6b413262.jpg


[url=http://forums.evolutionm.net/showthread.php?p=3100326#post3100326]]

OK, here is a diagram of a properly configured dual catch can setup. Each can should have some form of filter media in it to help condence out the nasty crap you are trying to capture.... an open can works, but not nearly as well.

Keith

http://www.socalevo.net/gallery/albums/userpics/10991/normal_mURI_temp_228581b2.jpg

[gofaster87]

You dont need to connect the catch can back to the intake manifold on our small 4 cyclinder cars. Big motors benefit from the vaccum created

[GokuSSJ4]

I have one on the car, dual set up that is
here are some pics of a full functional catch can
http://www.saikoumichi.com/DC3_REV_B_MAIN1B.jpg
here is another one
http://www.saikoumichi.com/DC3_REV_B_SECT.jpg
maybe i should take some pics of the catch can installed :?

[GokuSSJ4]

here is a bit more information on the product :
Finally! The arrival of a oil catch can system designed to DO SOMETHING!

Let's keep it simple. Boosted engines need to keep oil out of the turbo, intercooler, and intake manifold. A catch can can do this...that is if it is actually designed to work the way it is supposed to.

Oil travels out of the valve cover in vapor form, not liquid, so why do the big name companies sell catch cans that work like overflow reservoirs?

The DC3 is designed to interrupt the flow of oil vapor enough so that it condenses inside, and minimizes the traces of oil can go where you don't want it to.

The incoming line has a vapor snorkel that keeps the incoming vapor far away from the exit fitting. The incoming vapor must travel through a maze of stainless mesh before it has a chance of exiting. This creates condensation, and the oil vapor changes into oil drops which will just sink to the bottom of each chamber in the DC3.

So, why 2 chambers ? Why not join the breather and the PCV line into 1 can?

The simplest way to explain it is this... The PCV system works in ONE direction. Under vacuum the flow comes from the valve cover through the PCV valve and into the intake manifold, during this time, the air that is being sucked out is being replaced by the air coming in through the breather hose. Air comes in, and air goes out through the PCV line. When 2 lines go into 1 can, there is NO VACUUM effect possible.

So, why does the breather need a can if the flow only goes in one direction?

Under normal conditions this may be true...but under extreme boost, the breather line may experience a strong vacuum effect and actually cause the PCV valve to leak, allowing oil vapor to be sucked into the turbine and the intercooler which reduces it's efficiency.

[Dagul]

Wow, I was thinking up an idea similar to this a couple days ago...

The guy doing a repair job on one of my rims said he knows an aliminum welder who should be able to modify a catch can I had purchased from another member...

My idea was to have it cut open and have a air tight dividing wall put in the middle and have an extra nipple welded on both sides of the wall and an extra drain port welded as well...

It won't be as pretty as that dc3 dual catch can but it should work in a similar manner and tuck neatly in the middle of the strut bar...

[Alfred@TTech]

The dual catch can system really works and is a good item to have for thos who really hate all that oil in their boost system. Also, many evo owners simply run the front vent to atmosphere and this creates problems, especially bad ones on big turbo cars The intake is under vacuum and under normal operation sucks out blowby. With this being unhooked and the rear pcv having a one way valve on it, whenever you let off the throttle a lot of white bluish smoke comes out of the pipe. The front pcv isnt hooked up to the intake, so almost none of the blowby etc is getting cycled out. You come out of boost, into vacuum, the rear 1way pcv valve opens and all the crap in your motor gets sucked into your engine. Hence the John Force like smoking behind your car. Its not an absolute necessity at some levels but its a great product and does what its supposed to.

Smogrunner has this unit on his 11.0 sec daily driven evo. So did MrCotija when he ran his 11.8. Both had the problems I listed. I had one for myself but donted it to a friend in need. I feel somehow left out of Gokkus elite JDM parts whore group. :mitsu:

Alfred

[gofaster87]

Interesting, I never had smoking bellowing out on my big turbo car. I dont have it happening now either but then again my vent holes inside the valve cover were made bigger to vent more gasses. On another note a dual can isnt needed, both lines can be vented to one single can. It still amazes me why people spend a fortune on expensive catch cans. The money should be spent towards proper fittings and lines if anything.

[Dagul]

Interesting, I never had smoking bellowing out on my big turbo car. I dont have it happening now either but then again my vent holes inside the valve cover were made bigger to vent more gasses. On another note a dual can isnt needed, both lines can be vented to one single can. It still amazes me why people spend a fortune on expensive catch cans. The money should be spent towards proper fittings and lines if anything.


Vent holes made bigger? How so?

As for a dual catch can not necessary? How so? If both lines were connected to one catch can wouldn't the pressure in the manifold create pressure in the crackcase by backflowing into the valve cover vent without the PCV? Wouldn't that also pressurize the catchcan as well? I would like this explained before I spend the time and effort in modifying my existing catchcan...

[Saikou_Kun]

Hey this is cool! I didn't know this had been posted here. I got some updated pics and single versions too if you wanna take a look. The link is in my profile.

[tabio42]

To bring back an old thread - has anyone tried a vacuum pump to evacuate crankcase pressure?

[trinydex]

your turbo is a vacuum pump

[tabio42]

Yes - and so is an electric vacuum pump. The difference being that the electric vacuum pump doesn't feed low octane oil vapor into the combustion chamber and it can keep a vacuum when the turbo is under boost.

[trinydex]

are we not talking about the same thing? the compressor inducting air makes it a turbine molecular vacuum pump. that nipple that connects from the crank case to the intake is the vacuum line.

you only make vacuum under boost.

the intake doesn't feed low octane oil vapor into the combustion chamber and i don't even know what that means. are you saying you'd diesel oil vapors that are getting recirculated? isn't that what this thread is all about... catching the oil? and if it doesn't do so with perfection who really cares? are you gonna knock because of it?? what is the motivation here?

[tabio42]

Well I guess it would be an alternative to the catch cans. But it would be more expensive.

The PCV valve side is under vacuum when the engine is creating vacuum. So that is around 20" of vacuum until you touch the gas pedal and open the throttle plate. From there you are losing vacuum until the turbo spools right? Plus fresh air is coming in through the front side so I don't know how much vacuum is actually in there. Then when you are building boost the PCV valve closes and your turbo starts sucking air in through the intake.

Assuming that you are using a catch can inline on both lines, what I said about the oil is irrelevant. But do we know how much vacuum is created in the intake under boost? My intake doesn't have a nipple so I can't check. Can someone hook up a cheapy boost gauge and see? I can supply the boost gauge for testing.

[1]

great read, lots of info O0

[trinydex]

the vacuum in the intake is probably around 20" of mercury at boost.

the pcv is on the intake manifold so that's under vacuum until you touch the throttle like you said. but to keep that under vacuum all the time i think would mess with something that you don't want to mess with.

[tabio42]

I guess the amount of vacuum you get would also dependon the size of your turbo and the volume of your intake? You think that the vacuum effect gets weaker as your lines get longer?

[trinydex]

that stuff plays a negligable effect.