Quote:
Originally Posted by Calum
PCV systems exist for more than emissions, they help the engine by keeping blowby gasses from contaminating the oil, and they increase power by creating a vacuum on the bottom of the piston. The effects of this are shockingly large for what seems like such a small change.
Vent to atmosphere catch cans that completely disable the PCV system are snake oil at best, and slowly destroying your engine at worst. With the oil contamination they allow you really should be decreasing your oil change interval if you're running one. An oil analysis will tell you how often, anything else is just a wild ass guess.
Any street driven car, regardless of how much boost is can make, spends the majority of its running life with a partial vacuum in the intake manifold. If it takes 20hp to move your car down the road at highway speeds when its NA it doesn't suddenly take way more once you strap a turbo to it. Ok, the back pressure from the turbine might bring it up to 21hp, fine. The point is the engine still spends the majority of its life in a cruising state with a partial vacuum in the intake. There is absolutely no reason to not use a proper PCV system in a street car, especially these cars with D4S, you have the vacuum source readily available.
For race cars, I've seen people go to some pretty big extremes to get vacuum in their crankcase, vacuum pumps is where a lot ended up, but I saw a few drag racers using a port in the merge collector of their headers to pull a vacuum on their crankcase.
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If the crankcase is always in positive pressure because of blowby gases then why does the crankcase need vacuum to clear out the gases? There would be slightly higher crankcase pressures or resistance without the pull of the vacuum compared to atmospheric pressure, but it still should vent. I guess the thing to do is to test crankcase pressure when connected to vacuum versus open to atmosphere. Take the hose off the PCV, and air is constantly blowing out of it, so is vacuum really necessary, and wouldn’t venting it in any fashion keep the oil cleaner?
Most synthetic oil is good for more miles than I use. The AMSOIL says 1 year or 25k miles. I never wait that long. I would rather run open and minimize any oil and gases getting back into the intake.