There is a lot going on with crankcase pressure. My wife has pics of her grandpa, sitting on his RFD (rural free delivery) Silent Gray Fellow. The earliest pics show the bike just as Harley built it, when it was new. Within a few years it had grown some mods, including a BIG canister that looks like it collects the blowby and oil capture. This was back around 1914 or so. Nothing new under the sun, as Dad used to say.
Today, the manufacturers (pushed by government) are extending oil change cycles. The newer longer stroke fours are showing up with ports through the crankshaft web area of the block, directly under the bottom of the bores. Some have large, tuned oil separation chambers in the side of the block, to add volume in the oil recovery area. An important point is the tuning of that chamber for its MOST used engine rpm range. Continuous high rpm operation, with these techniques, can exacerbate oil consumption. Few customers have the patience to flog their daily driver hard enough to experience this.
With low tension Dykes ring packs, crankcase pressure balance has some effect on how quickly those low tension rings can seal on the compression stroke. I have seen misbuilt injection molded fittings that effectively sealed the crankcase (due to closing the crankcase air lines connected to the intake tract, before the throttle). The symptoms were mostly noticed at idle, with whistling crankshaft seals and slightly unstable idle.
Those low tension Dykes rings were showing up around 1980, in the new cars I worked on. They became possible due to improvements in the oil control ring and the attendant oil distribution ports in that land. Cylinder oiling is the job of the intake stroke and that oil ring control design. I was told at the time that low throttle operation (idle or decel) was the hardest part of ring seal with low tension rings.
I didnt quite believe that until the Igniter recalls of 1983. The timing was going into electronic advance at idle, so the ECU would pull back idle valve opening to slow the engine, and we were getting oil pooled in the dead catalytic converters! A new Igniter, new cat, and the weird oiling issue faded away.
I've always suspected that part of the early Honda success story was engines that held oil better than most brands. They enjoyed huge crankcase volume, compared to something like my '69 T120 Bonneville, because the clutch and trans could live on engine oil and share that huge chamber capacity to pump into. My CX based engines have giant caves for a crankcase, and I run a 5" piece of plain hose out of the factory crank vent chamber at the end of the crankshaft. So far, very little oil out of that simple hose. The earlier versions of this engine had dual vent chambers adjacent to each pushrod passage in the heads. They had twice the hose and much more volume in those chambers. And they leaked oil all over the engines.
Mysteries abound.
Regards, JimL