True, but hyd flat tappet and hyd roller cams will also pull past 6000 rpm if they are set up correctly. The cam test article that I linked to had a hyd flat tappet cam that I spun past 7000 rpm and my current hyd roller doesn't have any problem going well past 6000 rpm. But you do need to use the correct valve springs and the valve train does need to be in good shape. The type of oil and the oil pressure is also important when spinning a hyd roller past 6000 rpm. Chevy guys buzz the LS hyd roller cams well past 7000 rpm but that requires buying the correct parts.
