Those breathers defeat the PCV system. PCV stands for positive crankcase ventalation. The PCV system was the first smog device, starting as early as 1961. For normal street use, the closed PCV system is far superior to the old road draft tube that it replaced. The road draft tube didn't provide for any crankcase scavenging until about 25 mph. It also vented all of the blowby into the atmosphere, hence the reason for making the PCV system a smog device.
