Pcv ??

green1 said

So diluting your intake charge with exhaust gases, that don't burn, is better?

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Maybe you're thinking of the EGR valve which does inject exhaust gases into the intake stream - to cool the burn and reduce specific pollutants. A PCV allows the light evaporated gases (which DO burn) from the crankcase to enter the intake stream. The PCV keeps these lighter evaporation products from washing oil down from the cylinders.

PCV = always good (at least s for stock or moderate builds). EGR, only if your engine needs it.