P.C.V. : Open Vs Closed
It's very simple :
When at idle the PCV system sucks in clean air some where, it's better to use filtered air from the air cleaner than dirty / dusty air via the oil filler cap .
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-Nate
Geezer
'49 3100 235 W/ Muncie SM420 SOLD
'69 C/10 shortbed sidemount survivor 250 L6 W/ 350TH 
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