Without getting too technical, the transition from the base circle of the cam lobe to the area where the valve begins to lift is much shorter on a hydraulic cam since there's no need for a "clearance ramp" section of the lobe to take up the valve lash. The hydraulic lifter stays in contact with the cam lobe at all times. The cam profile on a hydraulic cam is completely different than a solid lifter shaft- - - -different lift rates, possibly different height and duration of the lobe lift, etc. Hydraulic cams can be ground mild to wild, high torque to high horsepower, depending on what the intended purpose of the cam happens to be.
Jerry
