On-topic (although arguably off-marque!) I have an Indian Enfield Bullet, bored and stroked to 625 cc. The standard breathing arrangement could not cope with the additional air volume variations beneath the piston, so I fitted an EGR valve from a 125 Yamaha (the same one as sold for use with Yamaha 650 twins and has been co-opted into use on many other bikes.)
Although it is used as an EGR valve in its original application, the point is that it is a one-way valve and ideal for use in crankcase breather applications.
It is a reed valve so it can cope with high-speed operation (although in the Bullet this is not essential.....) but the point is that it works. After the engine has been running, removing the pipe from the engine to the inlet of the reed valve results in a hiss as air is sucked back in to the crankcases.
The leaks, weeps, misted gasket joints etc. that the engine suffered from are a thing of the past.
btw, I've never heard of a vehicle engine breather system needing to inhale air from the outside before expelling it back through a pcv and then into the combustion chambers. it seems counter-intuitive to me....an air cooled crankcase? Of course, my experience is limited!
My old Rover P5B (3.5 litre V8) 'exhaled' from various points into the inlet manifold. The inlet depression helped 'suck' air from the crankcase to maintain a slightly negative internal air pressure inside the engine and prevent oil leaks.
There were filters in the breather hoses to the manifold (which also act to prevent a flashback) and if they became blocked the crank oil seals would leak like the Torrey Canyon (reference for our older members....)
Sorry for the off-marque diversions.