what spec is the engine???? if its rings they will smoke when you accelerate hard, not just on idle, it might just be running a bit rich on the top end and after you have poodled it home after a good hard blast she may just be a bit sooty and thats what your seeing
find out if its definatly oil first.......whip the plugs out if they are black and oily..its fooked, if they are black and sooty, get a tuner to check the fuelling for you