Not all performance parts are made equal. Hard as it may be to believe, sometimes flashy words or phrases are used to imply enhanced ability, even though that might not always be the case. With so many variations of rocker arms available, it can be difficult to discern which is actually best. The Hughes Engines Tech Center is quick to clear up why aluminum rocker arms like their 1506 models are generally a good bet:
We have had calls inquiring about stainless steel & iron rocker arms and would like to state our position. Stainless steel & iron are good, strong material for rocker arms and they claim they are stiffer than aluminum rockers. However, the aluminum dampens the harmonics better than steel. What the stainless steel people talk around is the fact that most do not have any bearing material in the bore. This means that you have a very hard shaft and a very hard rocker bore interface. This is not a good situation.
Normally one part, usually the bore, has a softer material which acts as the bearing. For example, consider engine bearings. In all engine bearings, the shaft is extremely hard and the bearing material is soft.
As a matter of fact, most engine bearings have a very thin coating of babbit on the surface. This babbit coating is very fragile and as you know can be damaged very easily. These types of bearings have much more stress and pressure on them than the rockers and they live for thousands of miles.
Two hard surfaces against each other is not a good situation. So, what can happen? Check out these pictures! These photos are of some stainless rockers and shafts. You can expect the same results from iron.
The rockers and shafts are badly damaged. No, they did not run out of oil. If they had, it would be indicated by a change in color on the surface of the metal. What actually happens is there is no bearing surface and the two hard surfaces micro-weld themselves to each other then break loose and then repeat this scenario over and over causing a snowball effect until they look like these photos or seize together. Not a pretty sight!
If the stainless rocker were bushed with a bronze or “plastic” bushing they could live. It is also interesting to note here that many of the NHRA and other pro racers run aluminum rocker arms. Some of the import stainless rockers have bushings, but they have other issues.