Precision manufactured roller rocker arms, made by Jims in the USA. The 1.625 ratio can also be used to replace OEM 17360-83 and 17375-83. The 1.7 ratio is for a custom valve train set up, where a super high lift is required. Roller rockers improve valve train geometry and efficiency. They always must be installed with adjustable push rods. Rocker shafts and push rods must be ordered separately.