I planning on buy this Cusco Center LSD
http://www.z1auto.com/prodmore.asp?model=wrx&cat=driveline&prodid=1152
the problem is that I'm not sure if it dose fit in my 2004 rs ?
I know that my rs dose not have a rear LSD but I'm going also to buy one with the cusco center lsd..
:frown: so what yiu think guys is that possible on a car with a different gear ratio than the WRX :shakehead

It SHOULD work, but you'll probably need to swap the ring gear out of the rear diff with one from a WRX so the ratio's will match.