It depends on your engine. In my IO-360 lycoming, I used to keep 8
quarts. Then, after about 500SMOH the engine started to blow out
anything above 7 quarts. It depends how much blow by you get on your
cylinders, I think. I teach in a Warrior, and I know the book says you
can run it on very little oil but I would want to keep at least 6
quarts in it.