That's a good question Rooster, and I would have included the answer above if, supper had not called me away A 'closed' system has a an inlet that draws air through the the intake filter, If you want a' closed' system you'll have to tap in to the air cleaner, pipe that to the inlet to the crankcase. For a 'closed' system the air would enter through the air cleaner snorkel , then into the crank case (through the valve cover or valley pan), then into the intake manifold, and through the combustion chamber. An open system allows air directly into the crankcase (valve cover or valley pan) then into the intake manifold ... thereby eliminating the need for a pipe from the valve cover (or valley pan) to the air filter