Just finished reading the article and found it very interesting how the author does recommend adding catch cans and one-way check valves in conjunction with the engine's PCV valve for FI applications. However, I'm not quite sure if this applies to just centrifugal type blowers or also with PD blowers as well In a forced induction system, the manifold is only providing vacuum (negative pressure) at idle, low speeds, and during deceleration. At higher engine speeds and periods of boost, the system is actually under pressure. If not controlled, the increased manifold pressure will flow backwards through the valve cover into the engine, creating positive crankcase pressure. Most PVC valves are designed so that the sudden high pressure of an engine backfire closes the valve, but even the best valves become contaminated with oil and dirt so that they no longer completely block off the manifold pressure. This problem can be addressed with the use of a one-way check valve. The check valve would work with the PCV valve to limit air flow back into the crankcase. However, the gasses must still be evacuated, and this requires the use of a second evacuation channel. Crankcase Ventilation System, Modified for Fixed Displacement Supercharger This schematic illustrates the basic setup The second evacuation channel is actually provided by the first part of the primary intake channel. This is only possible because that part of the system is bidirectional, allowing air to flow in both directions. When the intake manifold vacuum is high but supercharger intake vacuum is relatively low, air is pulled through the crankcase in the direction of the manifold. But when the manifold is pressurized under boost, the check valve completely closes off this part of the system. When that happens, positive crankcase pressure pushes the blow-by gasses in the opposite direction. Almost simultaneously, the air flow at the supercharger intake increases greatly. The increase in airflow results in higher vacuum at the supercharger intake, which draws in the crankcase gasses. Air/Oil Separators (Catch Cans) Catch cans are considered a requirement with any forced induction engine, including those with supercharger systems. Whenever the crankcase ventilation system is used to circulate crankcase gasses through the intake, the need to filter the air becomes even more urgent. Dirty oil vapor can coat the entire intake system, including the valves, with an insulating layer of contaminants that may also contain corrosive elements. This layer may interfere with proper cooling and heat dissipation as well as gumming up the works. Most importantly, oil vapor in the intake stream lowers the octane of the fuel/air mixture. This could cause engine-damaging detonation and all of the problems associated with it. Therefore, the intake of crankcase gas should always be filtered through an air/oil separator. It is important to use cans that contain oil baffles and/or some sort of filtering element. Those that require periodic draining are recommended, as the oil contained therein is contaminated and not well suited for re-use.