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Well, I definitely know what a catch can is, what it catches and its intended purpose.
Most of what they catch vapor-wise is a non-issue. You just don't want liquid going into your intake and coking the back of the intake valves. Routing ALL of that it catches back to the oil pan is a NON-ISSUE. The water vapor will boil off, the rest condenses and is recycled back into the oil.
Again, the purpose is to keep that stuff from coking the back of the intake valves. That only happens because of too much flow-through from the fresh air side to the PVC side in the "proper case" and in the "improper case" from the PVC side to the fresh air side (which is the big concern with forced induction systems as they create a massive suction on the fresh air side compared to a naturally aspirated system).
OEMTech, thanks for the input, I have read your posts in regards to the PVC/Fresh air systems and even though a check valve will reduce the amount of oil ingested from the fresh air inlet hose before the turbo, the big concern is a lack of ventilation under boost that occurs with a check valve as you stated. Ie, too much crankcase pressure is allowed to build (anything above atmospheric is bad) because of the checkvalve (ie, under boost the PCV system is inoperable because there is no vacuum present, thus vacuum from the fresh air line is needed to make up for the evacuation. Again, you cannot get away from the fact that the vapors/pressure have to vent somewhere, and that ultimately is back to the intake.
So, it is well known that catch cans do have their place in forced induction systems, jsut that most high-end systems that are low-maintenance end up routing back into the oil pan. Again, not a big deal since at operating temp the water will boil off quickly and honestly not much will accumulate per run cycle.
It is only preventative maintenance to want to prevent as much of that to go into the intake in a liquid form as possible. You will always have some vapor that will make it back to the intake and get burned, you just want to condense out as much liquid as possible. Ultimately you only want to burn off the bypass gases and allow the oil and stuff to go back to the oil pan, all while creating as much of a vacuum inside the crankcase as you can to prevent leakage and allow all the seals to do their job, which is keep oil in under vacuum. Those seals are not designed and intended to operate under pressure, so you can never allow pressure to buildup in a crankcase, thus a checkvalve is an improper solution.
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