Stock rocker arms for Harley-Davidson® Evolution® and Twin Cam 88® engines have a rocker ratio of 1.625:1. Theoretically, that means that for every .100" of tappet travel (cam lift), the valve will move .1625". S&S 1.725:1 ratio rocker arms are designed to increase valve lift without increasing lifter travel. For the same .100" of tappet travel, the valve will theoretically move .1725" with 1.725:1 rocker arms. A cam designed for .600" lift with stock rocker arms will produce .637" valve lift with 1.725:1 ratio rocker arms. In practice, however, the valve travel will be slightly less due to deflection of valve train components, such as rocker arms and pushrods. High spring force at maximum lift makes this deflection loss more pronounced. In racing applications where very high lifts are required, a lower cam profile will reduce clearance problems between cam lobes and tappet guides and between tappet rollers and tappet guides.
Features and Benefits
- Additional valve lift can be obtained without increased tappet travel (cam lift)
- Forged from 8620 steel, then heat treated and shot peened for maximum strength and fatigue resistance
- Superior material and design makes them very strong and rigid eliminating stress areas that cause other rocker arms to break
- Rocker shaft bushings in S&S rocker arms are 3?4" long compared
to the stock 1?2" long bushings provides 50% more bearing support area to handle high spring loads
The use of 1.725:1 ratio rocker arms will increase stress on cams, tappets, and pushrods. For this reason they are recommended for racing only and not for street applications