Originally Posted by 1slow370

Phunk, the pcv valves on the 370z function the same way all pcv valves on all naturally aspirated emissions controlled engines function. They are flow metering check valves. the reason they rattle and the spring inside them is so weak is because they are set up to work with the amount of vacuum the engine produces, so that at idle the valve is open but only flows a little bit of air, because the high vacuum actually lifts the piston inside the valve off the seat and up to the top of the valve where it partially closes the exit orifice of the valve. This allows the system to vent but does not introduce enough air to effect the idle to great extent. when the throttle is opened pressure rises to the point where the piston falls to about the halfway point of the valve allowing much more fumes to be vented since the engine will be able to burn them effectively. when the motor back fires or boost comes on(if F.I.) the valve shut to prevent reversion of fumes into the intake. this is where the catch can does the most work because during boost the valve is shut but often leaks allowing boost to go through the valve, combine this with blow-by past the rings and your going to building a lot of crankcase pressure that can't go anywhere with the factory setup because it is trapped between the intake pipe and the manifold. this leads to popped out dipsticks and reduced power from having a boosted crankcase pressure(not much honestly though). When switching to an external pcv intake filter now the crankcase pressure under boost can escape by going backwards through the system all over your engine bay, which is where the catch can comes in. some systems i've seen have valves or solenoids that under boost will vent the catch can to atmosphere and under vacuum allow the pcv system to function normally the below method will allow you to vent crankcase pressure, without contaminating the intake, or reverting fumes all up under your hood, and for an estimated parts cost of 5-25 dollars.

And my personal favorite pcv system is the exhaust venturii, no oil stain under the hood, no reversion out the filters from blow by on a boosted car, and i can still imagine myself mystically choking up al gore's air every time i drive. Oh and it's by FAR the cheapest if you can weld or have a buddy who can because it involves two small pieces of tube cut on an angle and roughly 4 ft of hose. (also drilled out factory valves), using seperate pcv filters and plugging the intake pipes and the manifold hoses will allow you to eliminate any source of unmetered air caused by the pcv as well