Consists of 3 steel reeds that are normally in the closed position. When pistons travel downward in the cylinders, the air in the crankcase is compressed and pressure in the crankcase below the pistons increases. Pressure causes the reeds to open, allowing the air and oil mist in the crankcase to escape into the cam chest. When pistons change direction and begin traveling back upward in the cylinders, a vacuum is created in the close, preventing air from entering the crankcase. A slight vacuum is maintained in the crankcase and oil scavenging is greatly improved. Recommended on large displacement engines 100" or larger. Fitments: Harley Davidson FLHR Road King 1993 - 1998, Harley Davidson FLHR Road King EFI 1996 - 1998, Harley Davidson FLHRC Road King Classic EFI 1998, Harley Davidson FLHS Electra Glide Sport 1993, Harley Davidson FLHT Electra Glide Standard 1995 - 1998, Harley Davidson FLHTC Electra Glide Classic 1993 - 1998, Harley Davidson FLHTCI Electra Glide Classic EFI 1995 - 1998, Harley Davidson FLHTCU Electra Glide Ultra Classic 1993 - 1998, Harley Davidson FLHTCUI Electra Glide Ultra Classic EFI 1995 - 1998, Harley Davidson FLSTC Softail Heritage Classic 1993 - 1999, Harley Davidson FLSTF Softail Fat Boy 1993 - 1999, Harley Davidson FLSTN Heritage Softail Nostalgia 1993, Harley Davidson FLSTN Heritage Softail Special 1994 - 1996, Harley Davidson FLSTS Heritage Springer 1997 - 1999, Harley Davidson FLTC Tour Glide Classic 1993 - 1994, Harley Davidson FLTCU Tour Glide Ultra Classic 1993 - 1996, Harley Davidson FLTCU Tour Glide Ultra Classic EFI 1996, Harley Davidson FLTR Road Glide 1998, Harley Davidson FLTR Road Glide EFI 1998, Harley Davidson FXD Super Glide 1993 - 1998, Harley Davidson FXDL Low Rider 1993 - 1998, Harley Davidson FXDS-CONV Dyna Convertible 1995 - 1998