What is a dual catch can?
If you have read about the need for doing a walnut blasting to clean the valves... that is what this is all about. The cause of the dirty valves is due to the CCV dumping oily, yucky, blow-by sh$t back into the intake, across the valves and back into the engine to be recirculated instead of vented into our precious atmosphere. Furthermore, the valves do not get cleaned from fuel due to the direct injection system we have.
Many enthusiasts install a single catch can on the high pressure side only. There are a few points to be made here:
1) This is done because it certainly helps the problem
2) This is done because the high pressure side is accessible and is "easy"
3) What about the low pressure side? This is typically skipped because in our engines it is an internal system that is not readily adaptable to a catch can but is in fact the primary cause of severe fouling especially in cyl 4,5,6.
So... the low pressure side is where the second catch can in a "dual catch can" goes to trap some of the sh$t before it fouls up the valves. Our engine spends the majority of its life in low pressure PCV mode because it is not under boost most of the time hence contributes most to intake fouling.
Rob at RBTurbo can supply the parts to convert the internal, low pressure side PCV into an external PCV so that it can be routed through a catch can.
------------------------------------------------------
Some installation notes
A catch can should be as cool as possible in order to get the oil and water to condense and stay in the can as the cleaner air continues on.
This photo shows a location in a Z4 where the cans are in a cooler part of the engine bay protected by a heat shield:
This is where the crankcase ventilation system is.
The low pressure side has the internal PCV valve and the high pressure side is where the flapper hose assembly connects (I have already removed it in this pic)
This one has some notes to help see what is what. Note #4 should say cyl 4,5,6.
(This is best pic I can display with the text)
The External PCV is in place (see #1 above) and the flapper assembly for the high pressure side with the factory plastic pipe removed
Hose Routing. The high pressure side goes from the flapper, through a can, back into the rear turbo inlet pipe.
The new, low pressure external PCV port goes through a can then routed into the intake port.
Rob can supply a convenient adapter that gives you a connection to the intake or you can drill and tap the intake for the new line.
Final note:
The low pressure side catch can is a great improvement on its own, but the solution is not 100% effective unless you go all the way. The internal PCV system routes the blow-by into the intake internally inside the valve cover and these internal passages into the intake are still open.
The ultimate step in this process includes plugging those internal passages.
If you have everything you need and are doing a valve cover gasket project, plugging these passage takes about an hour. Here is a video of the process:
If you have read about the need for doing a walnut blasting to clean the valves... that is what this is all about. The cause of the dirty valves is due to the CCV dumping oily, yucky, blow-by sh$t back into the intake, across the valves and back into the engine to be recirculated instead of vented into our precious atmosphere. Furthermore, the valves do not get cleaned from fuel due to the direct injection system we have.
Many enthusiasts install a single catch can on the high pressure side only. There are a few points to be made here:
1) This is done because it certainly helps the problem
2) This is done because the high pressure side is accessible and is "easy"
3) What about the low pressure side? This is typically skipped because in our engines it is an internal system that is not readily adaptable to a catch can but is in fact the primary cause of severe fouling especially in cyl 4,5,6.
So... the low pressure side is where the second catch can in a "dual catch can" goes to trap some of the sh$t before it fouls up the valves. Our engine spends the majority of its life in low pressure PCV mode because it is not under boost most of the time hence contributes most to intake fouling.
Rob at RBTurbo can supply the parts to convert the internal, low pressure side PCV into an external PCV so that it can be routed through a catch can.
------------------------------------------------------
Some installation notes
A catch can should be as cool as possible in order to get the oil and water to condense and stay in the can as the cleaner air continues on.
This photo shows a location in a Z4 where the cans are in a cooler part of the engine bay protected by a heat shield:
This is where the crankcase ventilation system is.
The low pressure side has the internal PCV valve and the high pressure side is where the flapper hose assembly connects (I have already removed it in this pic)
This one has some notes to help see what is what. Note #4 should say cyl 4,5,6.
(This is best pic I can display with the text)
The External PCV is in place (see #1 above) and the flapper assembly for the high pressure side with the factory plastic pipe removed
Hose Routing. The high pressure side goes from the flapper, through a can, back into the rear turbo inlet pipe.
The new, low pressure external PCV port goes through a can then routed into the intake port.
Rob can supply a convenient adapter that gives you a connection to the intake or you can drill and tap the intake for the new line.
Final note:
The low pressure side catch can is a great improvement on its own, but the solution is not 100% effective unless you go all the way. The internal PCV system routes the blow-by into the intake internally inside the valve cover and these internal passages into the intake are still open.
The ultimate step in this process includes plugging those internal passages.
If you have everything you need and are doing a valve cover gasket project, plugging these passage takes about an hour. Here is a video of the process:
