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Old 05-12-2006, 05:59 PM   #1 (permalink)
 
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Oil catch cans and the PCV system.

I did some research so I could answer this question 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
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Old 05-12-2006, 06:03 PM   #2 (permalink)
 
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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
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Old 05-12-2006, 06:04 PM   #3 (permalink)
 
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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
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Old 05-12-2006, 06:06 PM   #4 (permalink)
 
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My current setup only has catch can #1 of the dual catch can setup because I have a sheet metal intake manifold that does not have a nipple on it for the PCV valve to connect to. Simply put I do not have positive crank case ventilation on my setup and as a result I do oil analysis (blackstone labs oil test system) to determin when to change my oil since I will get more blowby gasses, water vapor and whatnot in my oil than a car that has a correctly operating PCV system. My car is a weekend toy, but if I was going to use it as a daily driver I would go to the trouble of getting another nipple installed on my sheet metal intake and add the second catch can.

Keith
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Old 05-15-2006, 08:10 AM   #5 (permalink)
 
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Even if you run the dual can set-up like in your diagram, you still have to run a PCV valve, and you'll still have a boost leak.

And if you wanted, you could always run a single vented can, with two inlets, as apposed to running two catch cans.

Have you ever considered using the exhaust for a negative pressure source to pull the pressure and blow-by from the crankcase?

We are discussing this over on dsmtuners right now, and I am one of the people concerned about blowby contaminating my engine oil. But I still have not decided which method is best to use.
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Old 05-15-2006, 12:46 PM   #6 (permalink)
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Welcome 99gst_racer. Glad to see you here.
Could you link the tread from dsmtuners when you get a chance?



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Old 05-15-2006, 02:39 PM   #7 (permalink)
 
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Quote:
Originally Posted by turbolarry
Welcome 99gst_racer. Glad to see you here.
Thanks. I've actually been a member here for a year now, I just never posted until now. Chris brought this thread to my attention.

Quote:
Originally Posted by turbolarry
Could you link the tread from dsmtuners when you get a chance?
Sure, here's the link to the original thread: http://www.dsmtuners.com/forums/showthread.php?t=226155

We are also discussing it in the other part of the forum as well, but a link there will do you no good.
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Old 05-15-2006, 02:59 PM   #8 (permalink)
 
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In a nutshell, I no longer want to run a PCV valve. I don't want to take the chance of it being a boost leak. But therein lyes the problem. I still would like some sort of negative pressure (vacuum) source to help pull (evacuate) the crankcase pressure and all of the blow-by in there. I don't feel it will adequately evacuate itself without the help of a pressure source on the other side.

Here is how I have mine set-up currently:



This is a decent set-up, IMO. It is about as good as it can get, without having that negative pressure source that I am looking for.

I would rather not use the intake manifold for a vacuum source, unless I could find a one-way check valve (PCV valve) that was guaranteed not to leak on turbocharged applications. And I don't feel the intake tube will supply enough vacuum to make much of a difference in the evacuation process.

So, this leads me to my next idea. To possibly use the exhaust to evacuate the crankcase.



What do you guys think of this set-up?

My largest concern is oil contamination. I did a compression test yesterday, and the results were very pleasing. But I am still getting a large amount of blow-by. I could only imagine how much of that doesn't make it's way out of the crankcase and contaminates my engine oil. That is my concern for a negative pressure source for the crankcase.
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Old 05-16-2006, 01:32 AM   #9 (permalink)
 
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Quote:
Originally Posted by 99gst_racer
Even if you run the dual can set-up like in your diagram, you still have to run a PCV valve, and you'll still have a boost leak.

And if you wanted, you could always run a single vented can, with two inlets, as apposed to running two catch cans.

Have you ever considered using the exhaust for a negative pressure source to pull the pressure and blow-by from the crankcase?

We are discussing this over on dsmtuners right now, and I am one of the people concerned about blowby contaminating my engine oil. But I still have not decided which method is best to use.
As shown on the diagram it does have the PCV valve, and the potential for a boost leak. If you don't think the PCV valve is good enough you can find high quality high pressure check valves in any store that specializes in air fittings and use that instead. You do need a strong catch can that will not collapse under vacuum though.... I didn't consider this untill it was pointed out by someone else. I have a simple cylinder that would hold up fine, but some of the "box" type catch cans will collapse under vacuum.

A simple vented can is better than nothing, and is in fact what I am running now since I don't have a vacuum fitting on my sheet metal intake manifold to connect to the PCV valve... but without the PCV system operating you will end up with more contamination of your oil system. I used to do oil analyisis once in a while just to see how things were going in my engine, now I will be doing it every 5000 miles without fail.

Keith
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Old 05-16-2006, 01:39 AM   #10 (permalink)
 
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Quote:
Originally Posted by 99gst_racer
In a nutshell, I no longer want to run a PCV valve. I don't want to take the chance of it being a boost leak. But therein lyes the problem. I still would like some sort of negative pressure (vacuum) source to help pull (evacuate) the crankcase pressure and all of the blow-by in there. I don't feel it will adequately evacuate itself without the help of a pressure source on the other side.

Here is how I have mine set-up currently:



This is a decent set-up, IMO. It is about as good as it can get, without having that negative pressure source that I am looking for.

I would rather not use the intake manifold for a vacuum source, unless I could find a one-way check valve (PCV valve) that was guaranteed not to leak on turbocharged applications. And I don't feel the intake tube will supply enough vacuum to make much of a difference in the evacuation process.

So, this leads me to my next idea. To possibly use the exhaust to evacuate the crankcase.



What do you guys think of this set-up?

My largest concern is oil contamination. I did a compression test yesterday, and the results were very pleasing. But I am still getting a large amount of blow-by. I could only imagine how much of that doesn't make it's way out of the crankcase and contaminates my engine oil. That is my concern for a negative pressure source for the crankcase.
Your exhaust system is at positive pressure, so this would not work... even though after the turbo it is not at high positive pressure, it is still positive.

Also, the point of a PCV system is to have fresh airflow into the crank case, then the fresh air picks up the water vapor and other blowby gunk and is sucked out through the PCV valve into the intake manifold. If you do not have a fresh air source you don't suck anything out.

Think of it this way, if you take a glass beer bottle tilt it back and draw a vacuum in it with your mouth while drinking the beer eventualy flow stops because air can not get into the bottle.... but if you had a valve on the bottom of the beer bottle to let air in you would have constant flow of beer and life would be good

Keith
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