The upper pulley on the Jaguar XKR is more commonly exchanged, but those of you who are looking for the next steps and additional performance, we can also change the lower crank pulley driving the supercharger pulley. Doing this will have a dramatic improvement on power delivery and will gain further increaes to throttle response by up to 38bhp. NOTE - In order to supply our Jaguar XKR supercharger crank pulley, we do need you to send us your original crank pulley, as we physically mill and machine the original pulley