Does any body know what is the best spark plug for the xf.

 

Not having had any experience on the Xfire as yet (from working on it) But having a lot of experience on other vehicles, the Bosch platinum splitfire is a great plug.If you can index them, so much the better. Depending on what your driving conditions are most of the time, you might check on getting a slightly hotter (or colder) plug than the standard stock replacement.