The problem with aluminum rocker arms is that they break once they reach a certain number of cycles. Steel won't break if the load is below a certain level, but aluminum will always break. That is why OEM rocker arms are always steel. Racers get away with aluminum rocker arms since they don't run a bunch of cycles and because they replace them every few seasons. Street guys can run aluminum rockers if they don't drive very much. If you put a lot of miles on the car then eventually the aluminum rockers will break.
