The stock Hemi rocker arms use a nominal 1.5:1 ratio. Minor ratio variations have been found and are not unusual, although this can have a direct impact on the engines performance, both good and bad.
For most rebuilds, not intended for all-out racing, the small changes are not an issue. For high-performance rebuilds, the small ratio changes can be corrected by tailoring the cam profile to incorporate the variation. It is not considered practical to re-machine the rocker arm to make corrections for the casual engine rebuild. For more high performance orientated rebuilds, during the course of a rocker assembly rebuild it is possible to make minor adjustments to the rocker ratio but it is an additional step in the rebuild process, and as is to be expected, adds to the rebuild cost.
For solid lifter (mechanical) assemblies the adjustable rocker arm is preferred to an adjustable pushrod only from a maintenance standpoint. The OEM adjustable rocker assembly (Chrysler 300, Marine and truck) is a very strong, very durable unit but is also heavier than desired. Aluminum replacements have been made but, due to their needed bulk, are not exactly lightweight. The advantage is in the ability to machine the aluminum piece with varying degrees of ratio.
We have investigated the possibility of producing investment cast Titanium rockers and the research is on-going.
Non-adjustable rocker arm assemblies are commonly use in conjunction with adjustable pushrods for all types of engine rebuilds, from stock to high performance, including both mechanical and hydraulic lifters. Non adjustable rocker arms and adjustable pushrods, when used with a hydraulic lifter, provide the very necessary ability to properly pre-load the hydraulic lifter to the recommended specifications. This pre-load is extremely difficult to accomplish without some form of adjustment.
In the OEM configuration, the entire assembly was designed with a particular pre-load and the associated parts were then manufactured to this specification. Fast-forward 60 years. Many changes have occurred in the engine world and the oem parts necessary to simply replace a worn component are likely unavailable, in the original configuration. Additionally, during the course of many rebuilds, there are multiple machining operations that adversely affect something as simple as the lifter pre-load; Re-surfacing of heads, blocks, valve tips, valve seats, re-profiling the camshaft or even using a different thickness head gasket all change the pre-load. This all points to the use of an adjustable pushrod with the non-adjustable rocker arm.
As an option, for stock rebuilds, as well as high performance use, the stock, non-adjustable rocker arm, can be converted to an adjustable style by adding the needed adjusting screw. This is a precision machining operation and accomplished with the use of special jigs and fixtures. The exact process is proprietary information.
These photos are of a Dodge Hemi rocker assembly, fresh from rebuilding with the modification to convert them to adjustable. These adjustors require cups on the pushrods.
This a photo of a Chrysler rocker with the similar added adjustor. This adjustor requires a ball-end pushrod.
