Just to make sure does air pump out of the breather holes on the heads ,
If the motor is sealed up tight and the breather valves are working correctly, yes.
Next time you do an oil change leave your dipstick in when you remove the drain plug. After a quick spurt the oil drain flow should choke down to a trickle. Then remove the dipstick and it should drain freely. That is a good test of your breather function if it behaves in this manner.