I just finished R-2800: P&W's Dependable Masterpiece and noticed there's no mention of a pump for crankcase ventilation. Is this handled by the oil scavenge pumps?
In a car the combustion gasses that blow past the piston rings are sucked out by a line connecting the crackcase to the intake manifold by a check valve (the PCV valve). The suction "pump" is from the low pressure in the intake manifold. Cars before the PCV valve (developed in the 50s) just vented the crankcase gasses overboard through a hose. Aircraft engines, including the big radials and the Lycoming engine on my own plane, do the same.
Positive crankcase ventilation was probably the first pollution control device developed for cars. Piston aircraft engines have never used pollution control devices. They still use gasoline with lead in it.