Kingtal0n

Oil causes engine knock because it does not burn (well) in the combustion chamber, and tends to raise the compression ratio

You do not want oil anywhere except lubricating your parts. the fact it has to drain into a pan and circulate around seals is a necessary evil of trapping it in your engine.


YES you said this very well, I agree. You are pulling something out because all engines provide... vapour.

Where does the vapour go? And when is it produced? You are looking at the catch can as a place to put the vapour, should it decide to condense to a... solid or liquid... or a combination of both ("sludge?").

HOWEVER

During most normal driving, that is, when vapour is present due to a running engine, you are sucking it right into the intake manifold. does anybody run a catch can on their intake manifold PCV valve?

furthermore
During situations of full throttle boost, yes you utilize something besides your intake manifold PCV valve. Vapour produced is in a gaseous state, right? And the gases may condense to form liquids or even solids at some point after cooling, or coming into contact with other solids that provide surfaces for catalysis (why put steel wool in a catch can?) If they remain gasses, the engine will consume them, regardless of whether you have a catch can or not. So we are really only concerned with catching liquids, and solids in our catch can. Furthermore, we are not protecting the engine from these compounds, because it is highly unlikely they would have made it past the intercooler, or even the compressor outlet. Theoretically we are only really protecting our turbocharger inlet, and perhaps the compressor wheel/housing itself from potential "sludge". Which I agree with, good idea, well worth installing such a device. Which is why I have one.

Just don't be thinking it has anything to do with the engine, because as I pointed out already, the full time vacuum of the engine pulls non-filtered vapour directly out of the valvecover and into your intake manifold, and anything coming out of the valvecover during boost in a gas state, that remains in a gas state, is not going to stop in the catch can.

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jr_ss

That's why you increase the surface area inside a catch can with steel wool or another suitable material. Then the oil vapor condenses on it rather than just passing through.

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