Now the Krank Vent: During idle and partial throttle operations, the flow of gases is from the back side of the pistons (crank case blow by gases), through the PCV valve, and into the intake manifold. The driving force for this flow is the partial vacuum of the intake manifold. There is no flow through the front valve cover breather because the Krank Vent valve connected to it is kept shut by the partial vacuum. At full throttle, there is no vacuum generated, the PCV valve and the Krank Vent valve connected to it shut, and the blow by gases are relived through the front valve coved Krank Vent, which is no longer held closed by the vacuum, into the intake manifold.
So, from an EPA standpoint, whats the difference? Not a whole lot except the Krank Vent system is better at getting rid of blow by gases. With the stock system the flow of gases occurs mostly in the valve cover area fresh air mixed with blow by gases which rise to the valve cover area by convection. In the case of the Krank Vent, all of the flow is blow by.
So what are the advantages of the Krank Vent and a vacuum in the crank case? Heres how I see it:
1. Piston rings seal better so you burn less oil.
2. You get better flow in the oil return line of the SC or turbo
3. And most importantly, you prevent boost pressures from entering the crank case, which will reduce your HP, possibly blow front or rear engine seals, and possibly destroy your turbo by backing up the oil return line. You only need one of the Krank Vent valves for this one.
There may be other advantages to running a vacuum in the crank case that I am not aware of. I know that NASCAR and NHRA dragsters run external vacuum pumps for this purpose, and I know that these guys usually know what they are doing.
I believe I was the first on this forum to use the Krank Vent. Ive been using one for almost 3 years with no negative effects. I change my oil every 3000 miles or every 6 months, whichever comes first, and I have never had to add any in between changes. And the oil remains pretty clean between changes.