Just some potentially interesting data to add to the discussion - I'm one of the people who has always battled against huge oil burps. My engine is from an early-ish model S1 ('54 plate) so no breather mods, and having had many many burps over the last several years, on and off track, both with and without a catch can fitted, and 2 rebuilds, I've tried to look for some patterns. Might be useful for anyone trying to come up with an explanation? Or perhaps just add to the confusion
Firstly, I'm convinced that for me, they only seem to happen just after
rapidly letting off
the throttle from very high revs. I'm talking above the point where you would hear the beep (so over 8500 minimum, though obviously I don't know the exact conditions as the burps usually catch you off guard!). Basically when you're really pushing it and suddenly let off
to decelerate. Rather than when still on the throttle, as most people seem to have described so far (well, no one has explicitly said)?
Secondly, for me at least, it never made a difference whether I was going in a straight line or in a high-G corner. In fact, I think more of my burps have happened going in a straight line, because that's when you usually let off the throttle - before going into a corner. I'm not saying it hasn't happened while cornering hard, but I don't think that's the root cause (though it probably doesn't help).
Thirdly, when it does happen, if I have my 500ml can fitted it usually completely fills the can, and sometimes there's even enough to overflow and still make its way into the intake and create a small blip of smoke out the exhaust (though less than there would be without the can, where it leaves a massive smoke trail). This can be after just having emptied the can on one or two occasions (e.g. track days), meaning the engine somehow threw out over 500ml of oil IN ONE GO
. So I don't believe the burp itself it is a gradual build up of oil (though it may be caused by a gradual buildup of crankcase pressure, maybe).
Finally, it was a long time ago now so I'm not 100% sure about this, but I don't seem to remember having as much of a problem before the engine was first rebuilt. It might have happened (I don't remember), but the engine had low compression anyway when I got it, which only got worse until I had it rebuilt (always the plan), so perhaps it never really pushed out enough performance to trigger it, being an old tired engine. I first noticed it once rebuilt and street ported, which is what prompted me to buy a catch can, and since then I've always kept the oil between 1/2 to 3/4 on the dipstick. This helped, but I still got the occasional burp anyway when pushing it. That engine ultimately failed a year later with a leaky water jacket seal, and was rebuilt again under warranty, this time upgraded to a bridgeport. It is still going strong today in a new chassis, and I seem to get less burps now but I'm not sure if that's just because I'm more careful / aware. I also installed an AEM intake, so maybe that has affected it, though I suspect that's just coincidence.
Something else to think about - when at high revs under WOT, although the mass flow rate of air is high, it is free and able to flow (otherwise you wouldn't be making power!). We are at high load, so as anyone who has ever played around with mapping or hooked up a boost/vacuum gauge will know, the pressure in the intake manifold should actually be theoretically pretty close to atmospheric, despite the engine gulping down huge amounts of air. But if suddenly the throttle snaps shut (still at high revs)... then that's a massive pressure change down to maximum vacuum (overrun conditions) - the biggest step change the engine will see in the shortest time period (biggest "differential"). Admittedly the strong vacuum is only present after the throttle, whereas the oil filler breather is connected just before, but I wonder if it being plumbed in so close to the throttle has anything to do with it... probably not but who knows!
TL;DR Basically I personally think the conditions to get it to happen are a buildup in crankcase pressure over time, then once it's high enough the burp is triggered by being at WOT and high revs (more or less redline), and quickly letting off, at which point there is a massive blow back of oil for some reason we're not quite sure of yet (the actual "burp"). But you don't see the effect until you get back on the throttle, at which point all that oil is then sucked from the intake into the engine, and THAT's when you get your smokescreen.
Just some ramblings with no direction in particular. Sorry for the essay