Should I be using a PCV valve on a '69 350 motor? Currently using just open ventilation on the valve covers and oil fill pipe on the manifold. What advantage will the PCV give me and if I go that route should I cap off all other intakes to the crank case (the valve cover breathers and manifold breather)? Why doesn't a PCV valve act like a big vacuum leak?? I realize there's a check ball in it, but it still seems to me it would let a lot of air into the intake manifold. Thanks !!!