hey guys ..i live in the caribbean..i have a singapore model impreza TS(ej16) 1.6 engine..i'm currently doing a ej20 swap.....would I have to change the rear diff in my car to accomodate the ej20's power ?? if so does it mean that i also would have to change the rear axles as well ??!! basically the entire rear end ????!!

If your only swapping the engine, then you'll be ok.(and by ok, i mean it will work. You may still break stuff depending on your driving habits) You might want to get a better clutch though. If your changing transmissions, then you need to worry about matching the final drive ratio of the transmission and rear diff.

as he said your tranny must match the rear diff ratio

axles .. probably not there are at least 6 flavors of axles
i would bet you have 22 spline axles most newer LSDs use 25 splines and then there are 2 flavors of dual spline axles
read this
http://forums.nasioc.com/forums/showthread.php?t=1184807