The Impact of Follower Diameter On Performance
When dealing with camshafts the most common valve train setups all incorporate a flat follower or bucket. The flat follower is used in everything from small block Chev's in the tappet/pushrod configuration through to the popular RB and 2JZ platforms with the cam bucket/DOHC setup. The joys of flat followers are their simplicity to create and their lightweight construction which lends itself well to high RPM. However, the main limiting factor with any flat follower is the maximum velocity that the profile can be designed for. This velocity is directly proportional to the lifter diameter, the bigger the lifter the higher the maximum velocity. The maximum velocity can be determined using the following equation: Vmax = (π/180) * (Lifter Radius - Safety) As a rule, we will typically look for one millimeter of safety radially around the lifter edge. The maximum velocity goes on to determine other factors of the valve motion, most notably it determines the maximum lift that can be run at a given duration with a given base circle diameter. The picture above shows two profiles, both have 10mm lift and both have 230 degrees of duration at 1mm. However, the blue profile is designed for a standard 2JZ with a 28mm shim on top of the bucket while the red profile is designed for a 2JZ with a shim-less or shim under bucket setup which allows the entire 31mm diameter to be used. It is easy to see the area gain of the red profile as well as the potential for more lift to be used.