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The catch can removes oily contamination from the PCV system before it would have otherwise gotten into the intake. You do not want to breathe a bunch of oil into your engine. The deposits can form on the back of the valves and it can cause knock if the contamination is bad enough. GM designed an emissions control system to contain and burn the contaminants that requires no maintenance but your engine will be burning the crap if you do not add a separator (catch can) to remove it before it gets burned. You can do better if you are willing to spend a little money to buy a separator and do a small amount of maintenance once in a while by emptying the can.
Forced induction may require a different catch can setup than a normally aspirated car. The FI engine will not have vaccum during boost so the basic catch can will not do its job under boost. Any crankcase pressure and vapors would back up in to the intake at that point without something to prevent it. You dont want to just add a check valve because the excess pressure (and engine oil) WILL come out somewhere and it could be your engine seals. Not good!
If you arent that worried about the contamination during boost because it does not happen that often then the standard can setup will work for you. A little bit of crud will try to back up into the intake under boost but not that much. Certainly less would get burned than what you would get without any catch can at all. If you want to eliminate the crud under all operating conditions you may need a special catch can designed for boosted cars or 2 separate cans would work as well. The second can needs to be one without a check valve as it would pass air in one direction during non-boosted operation and act as a separator when under boost when the air is flowing in the opposite direction.
-Mark.
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