Comp Cams XFI SPR ("Springs and Phaser Mods Required") Camshafts are the best way to achieve the most horsepower and torque gains possible on the popular Ford 4.6L/5.4L Modular 3 Valve engines. This group of cam sets are available for naturally aspirated & supercharged engines; each version is offered in three performance levels. Designed to work with a modified Ford variable cam timing (VCT) system, these cams are direct replacement components. Working with Comp Cams Phaser Limiter Kit, XFI SPR Camshafts optimize both low and high RPM performance. As noted by the Comp Cams engineering staff during dyno testing, these camshafts provided the biggest power and torque improvements of any cam series they've ever tested in the Ford Modular 3 Valve engine.