I've been watching all of the conversations, in multiple threads, on the 'philosophies' of oil separation/catch cans and the theories of how to minimize oil getting into the turbo/intercooler/intake manifold. We all know this is not an ideal situation for any engine and results in less than ideal conditions from carbon build up and loss of performance.
For NA engines, setting up an oil separation system is much simpler than a boosted engine by putting a catch can between the valve cover outlet and the vacuum port on the intake manifold. For a SC or TC engine, which should in practice require the same basic set up, requires addressing both the vacuum side and the boost side of the intake system.
The following are my thoughts on an answer to the TC engine, since this is what I have, and is the path I believe I will be following - unless some other information that contradicts my solution theory is posted. This is not THE solution, as I am sure there is more than way to resolve this issue, and I'm sure others have their own opinions on whether this solution would work for them or not.
Pirating from KSLunsfo's original TC diagram and the edit from Torchandregdoc I have added to it to show what I am explaining in my theory:
-The filtered air input at (3) in the valve cover needs to be pulled off after the MAF, so it is 'metered' and accounted for by the ECM in the total air volume entering the engine. I believe this is the way the factory intake tube port is split off to go to the valve cover thru a check valve. I am on the fence if the check valve is needed for this line or not, but understanding that blow-by, especially under boost, can create a good amount of crankcase pressure that could force its way backward into the intake tube if no check valve is installed.
-The turbo port (A) is always under vacuum when the engine is running and the intake manifold port (B) will vary between vacuum (off throttle) and boost pressure (on throttle). These are the two sides of the system that need to be kept separate with any solution.
-Because (A) is under vacuum, a catch can #1 should be installed between (2) in the valve cover and the turbo intake port to eliminate as much oil vapor from entering the turbo as possible. This oil vapor may or may not coke up the intake turbine, but it will find its way into the intercooler, where it will condense into liquid, and contaminate the interior that reduces cooling efficiency. It can also affect the MAP sensor and, in the extreme, end up in the intake manifold.
-Port (B) under boost will be blocked by the PCV to prevent boost pressure from bleeding back into the crankcase. Under vacuum the port (B) will pull oil vapor from the engine into the intake manifold. Assuming the PCV functions correctly, catch can #2 should be installed between (1) and the intake manifold to capture this oil vapor. I believe this is the source of the majority of the oil being found in the intake manifold, as described by many, and adding this catch can will significantly reduce it.
My solution requires two catch cans, since the two sides of the intake system - before the turbo and after the turbo - must be kept separate to prevent messing up the air metering of the ECM and potential cross bleed of boost/vacuum. I also believe it is important to keep the (1), (2) and (3) port/line sizes close to the factory sizes - for a stock tune - to prevent messing up the 'expected' air metering for the system.
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