Who am I to challenge everything I see written on the net (especially that aseclub.net thread), but it seems as if everyone jumps on the same train without actually thinking through what is going on here.

For one thing, think about why there are two ports on the valve cover. When the throttle plate is closed, there is a high vacuum in the intake mani, and gas is sucked from the valve cover into the intake mani. This removes the corrosive gases that are trapped in the engine. But you still have these corrosive gases in the crankcase unless you have a total vacuum (e.g., like a 2gnt on the moon.) Oh oh, problem. Now let's introduce the 2nd port into the equation.

The 2nd port brings in air from after the air filter and before the throttle plate. When the throttle plate is closed, vacuum is created through the 1st port that is connected to the intake manifold. This creates a vacuum inside the valve cover, which creates suction through the 2nd port, bringing in FRESH AIR. Aha, now we have a real way to remove the corrosive gases in the crankcase. Fresh air dilutes the corrosive gases in the engine. Whereas a vacuum reduces the pressure, as soon as the vacuum ceases to exist, you still have these gases remaining in the crank, contaminating your oil.

So these methods of having BOTH ports go to vacuum with NO fresh air being introduced to the crank makes very LITTLE sense to me. But yay racecars do it, and if I see a single thread where a bunch of 2jz's do it then it must be mandatory...dumping oil straight into the exhaust, hey its okay there are technosophisticated things happening like Bernoulli's effect and magical rice pixies and who cares it's METAL. If you don't understand what is going on, add a check valve in a random location. Problem fixed.

Now look at this picture:

Wow that's awesome trendy font. And it's on the net. Let's use it! But wait a second, what new force is pushing oil out the 1st port and into the intake manifold, requiring a catch can? Remember vacuum pulls gases into the intake mani through that port on a NT with the throttle plate closed. We didn't need a catch can in that location then. Why do we need it there now that we have a turbo? Do we believe that during boost, that the crankcase pressure is greater than the pressure that is being created by your turbo, and air flows from the valve cover to the intake mani under boost? um well...

Yes sure the crankcase pressure is going to be higher under boost than it will be NT as you get more blowby past the rings, but if *you* were gas and had the choice of going through the 1st port through the PCV into a high pressure intake manifold, or through the 2nd valve cover port through a filter and straight to the atmosphere, which route do you choose? The answer is port number two. This is where oil will be blown out under pressure, and where a catch can should be.

Hey but what do I know I'm not even turbo. Please let me know what I'm doing wrong.

2gnt: '99 RS-T, killed by a toyota, pending rebuild...
Daily: Volt
Daily #2: '99 EVG ebike- STOLEN by PEDRO