A while back I was told to run a .060" - .080" orifice before the turbos oil inlet. I'm running a .081" right now and am not experiencing any oil blowing by the turbo seals. BUT my oil pressure doesn't go above 80 when cold and is at ~65 when warm above 2500rpm. Another thing you have to remember is to have a good drain for the turbo. Has to have a nice swoop down to the front cover to prevent "backing up" of the oil. I was told to run no smaller than a 5/8" line for the drain.