Yes you can if you want, I prefer not too on a street car. You will run a little leaner at idle/cruise because a breather introduces unmetered air into the engine. A lot of my friends have ran breathers, I prefer to keep the closed PCV setup myself. There is a lot of debate on this subject and many posts on corral.net and all the other forums as well. The cars I have ran breathers on had no PCV valve.