RG’s dyno testing has, so far, produced performance increases of 90 hp from an XK engine with stock 9:1 pistons, triple SU carbs and original cast iron headers (see below). More is made possible with Webber carbs or EFI and higher flow exhaust systems. Heads come with custom, seven bearing camshafts in two versions; one for use with the SU induction system and the other for Webber or EFI induction systems.
Depending on the condition of your original head, this higher quality and performance head can be a cost‐effective alternative to rebuilding. Have your head cleaned, pressure tested and inspected to see if rebuilding is even a viable option before deciding on what to do.