Aahh - I don't usually debate - because there are so many different (but still correct) schools of thought on virtually any engineering subject. But just to offer another perspective:
The use of a vacuum pump, or any other means to create an augmented crankcase vacuum only improves (ring face to cylinder wall) sealing in applications where low tension ring packs are used.
These rings are flexible and loosely fitting enough to allow them to react to the increased pressure differential that results when crankcase pressure is reduced.
Assuming that the pressure on the inner ring surface is mainly a function of compression ratio and remains constant, the only way to increase the outward force of the ring against the wall is by reducing the pressure on the outer side of the ring surface.
So, while it is true that low tension rings are able to take advantage of this greater delta P, the same cannot be said of a stock Chevy ring pack. As designed, stock rings do develop some outward force due to the pressure of combustion but not nearly what LT rings can achieve. They are just too thick across (5/64" on the compression rings and 3/16" on the oil control ring) and too rigid, to react like low tension rings.
And this is assuming that the stock rings and cylinder walls are in factory condition. But as the engine ages normally, the walls and ring faces wear and the original tight clearances begin to increase.
At some point, the ring to wall clearance hits the tipping point. It should be noted that; just like any other fluid, the pressurized gases created by the combustion process will always seek the path of least resistance. Eventually, due to the increased clearance/loss of tension between the cylinder wall and the ring face, the path of least resistance shifts. Now, more of the combustion gases start to leak by the outer faces of the rings instead of being captured behind them.
And (Boy, it took a long time to get here) was the basis for my comment:
Without an atmospheric vent, and with the intake system constantly pulling a vacuum on the crankcase via the PCV valve/hose, the pressure in the crankcase will soon turn negative. This negative pressure will cause even more blow-by of combustion gases across the piston rings and into the crankcase.
I was working on the assumption that the OP had a stock SBC with 100K miles (or so) on it. In that case, I still believe that the increased delta P created by the lack of an intake air vent will result in greater quantities of combustion gases leaking past the rings and entering the crankcase atmosphere.
