This is a set of 16 CatCams valve springs made specifically for the F4R 2.0 16v engine & will also fit the K4M engine They are a direct replacement for the original springs and are mostly used with up graded , high lift cams which can cause a standard spring to fully compress which can result damage to the valve train. They are also stiffer to help prevent valve bounce and this also helps the valves to close faster on high revving engines.