Well, 2 reasons, even well built stock motors get blowby to a small percentage, as there is an end gag in the rings. During the compression cycle some of the gasses that get blown by the rings is fuel and air. These gasses build up in the crankcase, and could potentionally explode :-(.
The second reason that after the fire shortly before the downstroke you will get blowby of exhuast gasses. This depending upon load can be a considerable amount which can build up pressure in the crankcase.
These gasses get vented into the bottom part of your engine. The PVC system is designed to extract these gasses and safely put them back into the intake, to be re-burned, and also to relieve any pressure buildup.
Hope this is accurate enough, and explains the process. You can however use a vacuum pump hooked up the the PCV valve as some racing engines do, but they are around 250 bucks.
I agree. The two biggies that were hit upon are that the PCV is closed (emissions friendly) and that the PCV actively scavenges the corrosive blowby gasses, where as breathers passively vent when pressure builds.
i'm in the same boat now, i'm torn between ditching my pcv and keeping it. i get oil in my intake and yes the lower intake baffle is in place and i'm using a home depot oil separator inline with the pcv and intake. the pcv system, even though it is efficient, seems to be more of a headache than its worth on cars like mine that are running superchargers. i currently am using a breather on my passenger side valve cover so i'm thinking of ditching the pcv and adding another breather either to the other valve cover or the lower intake where the pcv went. my car only gets driven about 2,000 miles a year and the oil is changed twice, maybe 3 times during that period. so i'm not really worried about the oil getting contaminated and the motor was just built last year so i shouldn't have any major blowby issues to deal with. so, to ditch it or not?
i dont think anyone would like that smell, where would this mist come from? i have an open breather in my passenger side valve cover (trick flows) and i have no oil coming out of the breather. these covers come without baffles so i had one welded in and its doing a great job of keeping the oil from splashing up and soaking the breather. i was thinking of doing the same to the driver side cover and ditching this pcv.
im running a breather on the drivers valve cover (thats where my filler neck is) and pcv to the lower intake. I have heard that a combination of a closed and opened system is bad
right now i have oil that blows out of my breather and dipstick. im not sure if it is because of of all the nitrous i used to have (wore the rings down) or if that by having a closed and opened pcv system blew it up.
next year, im going to have a fitting welded on my drivers side filler neck so i can run an entirely closed system and ditch the breather.