Originally posted by SleeperZ:
The air/oil seperator filters the oil vapors out of the air and feeds the filteres air back into the intake.
Where as a breather filter simply vents the filtered air into the atmosphere.
In the stock airbox there is a piece of foam that "acts" like a air/oil seperator, but the foam doesn't filter or flow well.
Its really just a personal choice if you want a air/oil seperator or jus ta breather filter.
Although some tracks (if you drag or auto-x) will not allow atmoshpere venting of anything.
Every track I have been to has allowed my breather. 
Hector
2003 Rally Red Mitsubishi Evolution VIII
257HP/259TQ
2005 Lapis Blue Mazda 6s
RET: 00 Cabernet Red Ford Contour Zetec ATX SUPERCHARGED
160HP/141TQ
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