Catch Can, Breathers and PCV

Shane361 · 06-14-2009, 12:55 AM

Curious on some of your guys take on my set up. My performance shop threw in a catch can as I asked but threw a breather on the pasenger side. Isnt this letting in unmetered air? Thinking I should run a hose from the passenger side around the back of the enging and T into the driver side which will send both into the catch can. Thoughts? -Shane

Mustangscotty · 06-14-2009, 02:02 PM

Please correct me if I'm understanding your post incorrectly. Air goes out of the breather and not into the valve cover, so unmetered air isn't an issue.

One issue I had with a breather was caught on video during a dyno run, the amount of air exiting the breather was such that it made the breather want to pop out. I ended up with a small amount of breather oil and engine oil being sprayed out all over the engine/ engine bay but only when the engine was under boost.

The cure? Installing a remote breather reservoir and is installed behind the drivers side fog lamp. When ever I do an oil change, I open up the valve to let any moisture/oil out of the reservoir.

Depending on the amount of boost, you may not want to install a breather tank. Lower boost means less oil spray coming out of the valve cover breather. Sean Hyland had the same issue on one of his mod motor cars. He made an air/oil separator which installs on the valve cover. Its effective but doesn't solve the problem, same for the water filters used in air tank lines. Seems the breather tank solved the problem 100%.

I really like the catch installed on the drivers side of your engine. Nice unit and by design its easy to tell it separates oil/air very well. But does it really?? Air under pressure makes it easy for oil mist to get past the catch and into your engine.

If it is as effective as you want it to be, why not run one similar to that on the passenger side? You can keep the stock line direction and not worry about emissions but still keep the air/oil separated.

One question remains, how will an open air breather affect your emissions? You live in Cali? It's easy to remove the breather and return your stock set up before emission testing.

gearmesh, inc. · 06-18-2009, 10:01 PM

Under light throttle with a functional PCV system, your crankcase will be under a slight vacuum in which the vacuum is regulated by the PCV valve. This enables your engine to burn off a lot of the combustion byproducts that sneak by the rings (blowby). If these gasses were allowed to stay in the crankcase, your oil would get dirty very quickly. The PCV system is widely considered an evil requirement of the EPA, but it will keep a street car's oil cleaner between changes vs. being without the PCV system.

The PCV system is never designed to deal with a large volume of blowby gasses, such as a boosted or heavily nitroused mill. What happens under heavy engine load is that the PCV system can't get all the blowby gasses through it so the engine can reburn the gasses, so there will be a backflow up into the fresh air supply side of the PCV system. This is the flow you see coming out of your breather under heavy throttle.

On a stock engine, you will notice that the air supply side of the PCV system will be taken somewhere off the air intake aft of the mass air meter, so this air that is drawn through the crankcase to purge it of blowby will be metered air. When you go to the breather in your picture, unmetered air is getting in the engine through the PCV system, but only at lighter throttles when the crankcase is under a slight vacuum. Under heavy throttle conditions when the PCV system can't handle the extreme blowby, you won't have any unmetered air under this condition because of the excess volume of blowby gasses trying to escape the crankcase. Keep in mind that blowby gasses are originally created by burning fuel with metered air in the first place.

The moral of the story is that you only get the unmetered air through your aftermarket breather under light throttle conditions. If you want to get totally rid of unmetered air, design a catch can for the fresh air side of your PCV system like you have on your dirty side, but in which the top of your catch can has a line that hooks up to the stock location on your intake plumbing, rather than an open filter that sucks in unmetered air.

Another thing to keep in mind is that the older an engine gets, the more blowby you will have due to worn rings. A just broken in engine will have less blowby than a worn engine.

Shane361 · 06-18-2009, 10:27 PM

Thanks guys, seems unmetered air is only during non-boost so there really isnt a huge probem here. Will look into a better route though. -Shane

Mustangscotty · 06-19-2009, 12:50 AM

Quote:

Originally Posted by Shane361

Thanks guys, seems unmetered air is only during non-boost so there really isnt a huge probem here. Will look into a better route though. -Shane

Do a search on ModularFords.com
tons of great information

06-14-2009, 12:55 AM	#1
Shane361 Senior Member Join Date: Aug 2007 Location: The Creek Posts: 2,622	Catch Can, Breathers and PCV Curious on some of your guys take on my set up. My performance shop threw in a catch can as I asked but threw a breather on the pasenger side. Isnt this letting in unmetered air? Thinking I should run a hose from the passenger side around the back of the enging and T into the driver side which will send both into the catch can. Thoughts? -Shane

06-14-2009, 02:02 PM	#2
Mustangscotty Senior Member Join Date: Dec 2007 Posts: 699	Please correct me if I'm understanding your post incorrectly. Air goes out of the breather and not into the valve cover, so unmetered air isn't an issue. One issue I had with a breather was caught on video during a dyno run, the amount of air exiting the breather was such that it made the breather want to pop out. I ended up with a small amount of breather oil and engine oil being sprayed out all over the engine/ engine bay but only when the engine was under boost. The cure? Installing a remote breather reservoir and is installed behind the drivers side fog lamp. When ever I do an oil change, I open up the valve to let any moisture/oil out of the reservoir. Depending on the amount of boost, you may not want to install a breather tank. Lower boost means less oil spray coming out of the valve cover breather. Sean Hyland had the same issue on one of his mod motor cars. He made an air/oil separator which installs on the valve cover. Its effective but doesn't solve the problem, same for the water filters used in air tank lines. Seems the breather tank solved the problem 100%. I really like the catch installed on the drivers side of your engine. Nice unit and by design its easy to tell it separates oil/air very well. But does it really?? Air under pressure makes it easy for oil mist to get past the catch and into your engine. If it is as effective as you want it to be, why not run one similar to that on the passenger side? You can keep the stock line direction and not worry about emissions but still keep the air/oil separated. One question remains, how will an open air breather affect your emissions? You live in Cali? It's easy to remove the breather and return your stock set up before emission testing. __________________ Scotty 67 Mustang fastback 68 Mustang coupe 03 Cobra 13 F150 4x4 69 Harley FLH 67 Camaro Last edited by Mustangscotty; 06-14-2009 at 04:23 PM.

06-18-2009, 10:01 PM	#3
gearmesh, inc. creepy azz cracka Join Date: Nov 2008 Location: Summerville Posts: 1,587	Under light throttle with a functional PCV system, your crankcase will be under a slight vacuum in which the vacuum is regulated by the PCV valve. This enables your engine to burn off a lot of the combustion byproducts that sneak by the rings (blowby). If these gasses were allowed to stay in the crankcase, your oil would get dirty very quickly. The PCV system is widely considered an evil requirement of the EPA, but it will keep a street car's oil cleaner between changes vs. being without the PCV system. The PCV system is never designed to deal with a large volume of blowby gasses, such as a boosted or heavily nitroused mill. What happens under heavy engine load is that the PCV system can't get all the blowby gasses through it so the engine can reburn the gasses, so there will be a backflow up into the fresh air supply side of the PCV system. This is the flow you see coming out of your breather under heavy throttle. On a stock engine, you will notice that the air supply side of the PCV system will be taken somewhere off the air intake aft of the mass air meter, so this air that is drawn through the crankcase to purge it of blowby will be metered air. When you go to the breather in your picture, unmetered air is getting in the engine through the PCV system, but only at lighter throttles when the crankcase is under a slight vacuum. Under heavy throttle conditions when the PCV system can't handle the extreme blowby, you won't have any unmetered air under this condition because of the excess volume of blowby gasses trying to escape the crankcase. Keep in mind that blowby gasses are originally created by burning fuel with metered air in the first place. The moral of the story is that you only get the unmetered air through your aftermarket breather under light throttle conditions. If you want to get totally rid of unmetered air, design a catch can for the fresh air side of your PCV system like you have on your dirty side, but in which the top of your catch can has a line that hooks up to the stock location on your intake plumbing, rather than an open filter that sucks in unmetered air. Another thing to keep in mind is that the older an engine gets, the more blowby you will have due to worn rings. A just broken in engine will have less blowby than a worn engine. Last edited by gearmesh, inc.; 06-18-2009 at 10:04 PM.

06-18-2009, 10:27 PM	#4
Shane361 Senior Member Join Date: Aug 2007 Location: The Creek Posts: 2,622	Thanks guys, seems unmetered air is only during non-boost so there really isnt a huge probem here. Will look into a better route though. -Shane