[dataway]

Yep, all that agrees with what I am saying.

The key thing to remember is air NEVER flows without a difference in pressure to create flow. Whether the difference is ambient to vacuum, or higher pressure to ambient. It always requires a difference in pressure to move air. ANY place that air flows, there will be a higher pressure at the source of the flow, and a lower pressure at the end of the flow.

So crankcase gases vented to the air cleaner .... which is at a slight negative pressure compared to ambient atmosphere will maintain a slightly lower than ambient pressure in the crankcase on a closed system compared to the older open systems at low rpm. At high rpm the crankcase almost always has a higher pressure than ambient unless you have some kind of additional evacuation system ... which some race cars do that run extended periods at high rpm.

Back in the day they would plumb the valve cover breathers to evacuation fittings in the exhaust .... and yes the right type of fitting in the exhaust will pull out crankcase gases during the negative exhaust pressure pulses.

F1 cars go so far as to try to pull high vacuums on the crankcase so pistons on the down stroke only have to push "rarified" air.

I'm not sure if you are understanding the point I'm making. A crankcase vented to the air cleaner in a closed system will maintain a lower pressure in the crankcase because the "Ambient" pressure it sees is air cleaner pressure .... which is at a slightly lower pressure than "open to atmosphere". The air cleaner HAS to be at a lower pressure than outside air, or air would never move into the air cleaner.

All this assumes a normal engine. A worn engine will produce so much blow by that the PCV can never draw it all out, and it will always have a pressurized crankcase ... and it will have mung and oil flowing out of oil filler cap, the breather tube, the air cleaner will be full of oil residue and the valve covers will probably leak.