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Rob@RBTurbo Rob@RBTurbo is offline
Posts: 4,039
Join Date: Feb 2009
Car: 335I
Default 04-27-2020, 10:42 AM

The "high side" flapper is actually dual purpose.

It closes under low load to allow small vacuum to be placed on the crankcase, and with the built-in orifice it allows clean filtrated air (ie. from the air filter rear inlet) to replenish the crankcase environment for "positive crankcase ventilation".

Then under high load it opens and basically does nothing aside for gets out of the way for forced ventilation with some small "vacuum" aid from the rear inlet.

You want to retain the flapper on the high side as long as you are retaining the PCV valve as part of your system.

Too many people over complicate this system by adding in too many parts they see available online, and wind up with some hodgepodge of a system that just doesn't work properly. Keep it simple out there guys, there is not too much that is needed to be done here for nearly everyone.


See for N54 Twin Turbo Bolt-On upgrades, or contact directly 314-630-8950 for a price quote.
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