A PCV loop is used by mfrs to meet emissions requirements and for no other reason. Using a PCV system without catch can, or some other mechanism to remove the oil from entering the air/fuel mixture, is a less than desirable approach. Getting more oil mist generally means more oil agitation ( high rpm, high boost, increased blow by) and is detrimental in the combustion chamber.so any thing that can be done to eliminate/minimize, especially on a DI setup, is desirable. Basically no 2 situations are the same, just as no 2 motors or drivers style. If you run a second catch can you would not need the breather cap.Ĭlick to expand.The amount of oil vapor is affected by many things including type/style of driving, short drives vs extended usage, overall condition of motor, specific cylinder sealing efficiencies, boost pressures (tuned or untuned), mods (catch cans, baffles, etc), engine oil wt and "freshness", ambient driving conditions.and so on and so on. For me a secondary catch can on the intake is preferred but both will work. If the breather cap doesn't have a check valve then the crank case is always open to the atmosphere (PCV system effectiveness is reduced) and you'd be more likely to vent mist into the engine compartment.Ī check valve breather is not a bad alternative to using one can (crankcase) for all but demanding track conditions, bc it would only vent under boost and excessive internal engine crankcase pressure. The upper PCV system draws air from valve cover area when the the car is creating an intake vacuum (partial throttle opening) but closes when the vacuum pressure in the intake tube drops (under boost or larger throttle openings).Īn oil cap breather should include a pressure check valve so that the only time it would be open is under boost when the rest of the PCV system is closed, in order to relieve internal engine pressure but with out venting into the air/fuel track. When boost is detected the crank case PCV or PCV on the catch can closes (no flow). If I recall correctly the way our system works is that the Crankcase side of the PCV system is open (drawing air from crankcase into the throttle body) when the car is drawing a vacuum (NOT under boost).
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