Vented Catch Can?
Tech Contributor
Joined: Sep 2005
Posts: 1,731
Likes: 82
From: New Market AL
There are 2 ways to vent the crankcase when it develops positive pressure:
1. Pull the air/oil vapor from a high point (valve cover), through a check valve (PCV valve), and route it back into the intake manifold to be used as combustion air.
2. Vent the air/oil vapor directly to the atmosphere (engine bay). Use a filter to keep foreign particles out of the crankcase.
A PCV system will reduce emissions and can help keep the engine bay cleaner, but it can also introduce quite a bit of oil into the intake stream if the crankcase is seeing positive pressure. By adding an oil separator (catch can) in the PCV stream, you can have the benefits of cleaner running without the problem of oil in the intake stream.
1. Pull the air/oil vapor from a high point (valve cover), through a check valve (PCV valve), and route it back into the intake manifold to be used as combustion air.
2. Vent the air/oil vapor directly to the atmosphere (engine bay). Use a filter to keep foreign particles out of the crankcase.
A PCV system will reduce emissions and can help keep the engine bay cleaner, but it can also introduce quite a bit of oil into the intake stream if the crankcase is seeing positive pressure. By adding an oil separator (catch can) in the PCV stream, you can have the benefits of cleaner running without the problem of oil in the intake stream.
Melting Slicks
Joined: Sep 2003
Posts: 2,062
Likes: 117
Thread Starter
Le Mans Master
Joined: Jun 2002
Posts: 9,220
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From: San Diego California
Former Vendor
Joined: Apr 2006
Posts: 2,470
Likes: 2
From: Portland OR
St. Jude Donor '10-'11-'12
debateable
The sytem is made to flow in one direction.
The engine sucks the air from the crank case ( via a tube from the valley cover and hose into the intake behind the tb) and replaces it via the clean air return which is through the valve cover.. so by placing a filter on top of the oil cap your doing the same thing basically. You want your clean air return filtered but the location of where that air comes from is semi important... in some models its a bad setup with the venturri effect reversing flow due to location of the clean air port in the throttle body.... so to avoid that you get rid of that line and draw air from the filtered cap... or move the line from the TB
The sytem is made to flow in one direction.
The engine sucks the air from the crank case ( via a tube from the valley cover and hose into the intake behind the tb) and replaces it via the clean air return which is through the valve cover.. so by placing a filter on top of the oil cap your doing the same thing basically. You want your clean air return filtered but the location of where that air comes from is semi important... in some models its a bad setup with the venturri effect reversing flow due to location of the clean air port in the throttle body.... so to avoid that you get rid of that line and draw air from the filtered cap... or move the line from the TB
Last edited by 99blancoss; May 26, 2011 at 06:59 AM.
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Le Mans Master
Joined: Mar 2002
Posts: 5,955
Likes: 161
From: PNW
Putting an open breather on the catch can doesn't make sense if the catch can is located in series between the valley cover and intake manifold. Under low throttle opening conditions (ie, high intake vacuum) there would be virtually no crankcase vapors drawn out of the crankcase because the intake would just be sucking fresh our through the breather and straight into the intake ... thereby not creating any fresh air flow through the engine.
Putting an open air breather on the oil filler cap (or somewhere on a valve cover) makes more sense because that will retain the correct fresh air flow path.
Putting an open air breather on the oil filler cap (or somewhere on a valve cover) makes more sense because that will retain the correct fresh air flow path.
Safety Car
Joined: Jul 2005
Posts: 3,572
Likes: 9
From: Jackson Tn
St. Jude Donor '06-'07-'08-'09
I use a duel can made by Saikou Michi and it works great
here is some good info
http://www.ls1tech.com/forums/genera...outing-ok.html
Last edited by printmanjackson; May 27, 2011 at 12:42 AM.
Former Vendor
Joined: Apr 2006
Posts: 2,470
Likes: 2
From: Portland OR
St. Jude Donor '10-'11-'12
I missed the vented can part and was thinking the vent on the oil cap....LOL But yes I would think your correct. The direction of flow needs to be kept the same and by venting the can your effecting that system. The SM can is one way/system but certainly not the only way. A good catch can and properly routed clean air retun line will do the same
