Mechanical "solid" lifters should be used in applications when hydraulic cams would surpass their maximum RPM potential. Mechanical lifters have no hydraulic mechanism to pump- up. Theoretically, with the correct cam and engine components, a mechanical lifter cam has an RPM potential of 8000 to 8500 RPM Mechanical lifters are noisier than hydraulics. The engine must have an adjustable valve train system. Valve lash must be set, periodically checked, and maintained. (Can NOT be used on a hydraulic design cam.)