It doesn’t matter if you have a high-compression big-block that’s a torque monster, or a small-block that screams to the highest RPM level possible — you need to make sure your valvetrain is sorted out. An important part that needs to be sized correctly are the rocker arms and their ratio. Going over the maximum ratio and offset for a rocker arm’s length is a problem you want to avoid.
The basic function of a rocker arm is to be a multiplier for the lift of a cam lobe as it’s applied to a valve. The rocker arm ratio that you typically see from 1.5 to 1.8, depending on the engine, is based on a relationship that is possessed by the two halves of a rocker arm.
The higher the ratio the rocker arm has the more lift it will provide, but that isn’t always a good thing. Trying to have an excessive amount of lift that isn’t matched to your valvetrain will cause geometry issues, not allow valve springs to function correctly, and allow the valve to contact the top of your piston.
Sheldon Miller from T&D Machine goes into more detail on why there is a maximum ration and offset for rocker arms of different lengths.
“We have a limit on how much ratio we can fit on a particular rocker length and offset. We keep a nominal amount of material around that adjuster to be sure that the rocker lasts a very long time. In most cases, the amount of offset the adjuster screw has is the biggest limiting factor. A rocker arm with zero offset is far more likely to be able to accept a high ratio than the same length body with a lot of offset.”
If you do need to go to a rocker arm with a higher ratio, there is a way to avoid some issues: T&D Machine will go with using steel as a material option to help make sure the rocker arms will last and not have any issues.
“The way we can fit a higher ratio in a rocker is building a rocker set that has a longer fulcrum length or, in some cases, going to a steel rocker option. With steel being stronger, the amount of material around the adjuster can be less. All factors are considered when selecting the correct rocker assembly and options for your combination,” Miller explains.
If you want to learn more about rocker arms and rocker arm ratios, make sure you check out the T&D Machine website right here.