If your referring to those little filters on each cam cover ? He should also disable the factory PCV system by capping off both the vacuum port to the intake manifold and throttle body prior to installing breather filters, otherwise running them with part of the PCV system still intact may cause a lean condition ..

It's also recommended to remove the integrated PCV valve from the underside of the driver's side cam cover prior to disabling the factory PCV system in favor of running breather filters..

 

^+1 Plus if you go with a 710 cap breather too it will all but eliminate any oil drippage that some complain about. I've never experience it but I have always run 3 open breathers on my motor.