Performance Ranked XK-1. Introducing XKs Unlimited's Performance Ranked Camshaft Selection. The choice of camshafts is a critical one for power output, and is often made without all the facts at your disposal. Most of the power increases in a Jaguar high performance engine build-up are made in the cylinder head. Increased flow by porting and the use of larger valves is necessary. So too is a camshaft dialed-in for the type of driving the engine is expected to endure. For an explanation see page 24E in the print catalog or refer to that page in the "Flip Catalog" section of the site.