Looks like nobody wants to answer that question...It would appear that we all agree not to disagree....LOL

All I've ever seen in my breather can is a milky condensation which is usually only during the winter months. If I were boosted it would be vented to atmosphere just as it is right now.

 

pretty much lol... i just wanted to not smell it when driving around normal.
had smaller hose going back to the intake with the MM check valve fitting at the can, seemed to work as far as in boost - but decel after a long pull was usually where id notice it smoking like it was sucking it all up when the kpa was way down there.

 

If you vent to atmosphere with the MM system, what does this system use for a vacuum source when under boost. It would seem that you need a vacuum source when under boost in order to draw excessive crankcase pressure into the can, scrub it, and then evacuate either to atmosphere or by recirculating back into the intake along with filtered air?

Some vent to atmosphere by running a long heater hose under the car thinking dirty air is expelled to atmosphere. What happens when you do that is the hose end acts like a venturi tube creating a vacuum drawing unfiltered air into the system.

 

The MM PCV can only maintains PCV function during idle, part throttle/cruise conditions when vacuum is present.
When boost is sensed, there's a check valve in the vacuum line the closes and the can then becomes a breather can and vents crank case pressure to atmosphere, hence the need for a large -10 or -12 AN line.
Since you're usually hauling *** when in boost, you'd never notice the oil smell anyways.
So I guess you can say its an either or can, its a sealed catch can and a breather can, just depends on how the engine is being operated.

 

I have no vacuum source to the cans now, they are just venting to atmoshere.

MM idea is to have a hose to the intake manifold for vac source with check valve on it. in boost the check valve closes and can vents to atmosphere. when under vacuum theres a rubber (or whatever material) disc in the filter that falls/holds and maintains vacuum to the intake.

 

There is a vac source available under boost - between the turbo and air filter , haven't measured it but it may be the reason my closed system works with -6 hose. Both cover vent to pre turbo, 1 through the catch can the other (pass side) straight through, have checked for oily residue in the turbo and pipes and nothing to speak of. The only reason I went this route was to avoid a 300$ + fine for open breather around here , been working fine . Might also be the stock 180,000 mile ring gaps

 

I did this but got oil residue on my turbo compressor wheel so I changed it but to avoid a fine I would have left it.