It is a fairly common mod, not as much on the XJs but the XFR and F-Type guys do it a lot. Crank pulley (front portion, the harmonic balancer is left on the car thus the crank bolt does not need to come out!) and an accompanying tune is almost all you can do to the AJ133 SC V8. You can do a SC pulley, but it only gives about 15 extra hp, 30lbs ft and takes like 4+ hours to change because the entire snout of the supercharger needs to come off (liquid intercooled). I may look into that IF my SC starts to begin its rattle of the coupler wearing out...then while I am in there...might as well.