Simply put, it removes the aerated oil the PCV valve is pushing to the upper..
Ever pull your upper intake and find oil all around your intake ports??? Your motors built some so I would thing you have it...most do....
I put on a intake spacer last Fall....they come like a Tan color...Mines Black now cause its soaked with oil getting pushed up...I knew it was doing it for years...Been bugging me since I noticed it...every time i pull the upper, oil in the ports... :damnit:
When I first removed the stock upper, I had no oil to speak of...alot of Black crud, no oil...Once I ported the lower....everytime I pulled the upper the ports were super clean...but oil was all around, and in em....I swapped on an Explorer, same deal, then the 93 Cobra, same deal again....I read up on these on Corner Carvers forum, lotta them use em....I just wanted to cure it more than anything...I gotta admit thought, my gas milage is up some since I added it..