Joe explained the differences in the solid and hydraulic cam profiles very well. The "acceleration ramp" is an area of slow lift that equals the clearance specification- - -for instance, a cam with a clearance specification of .006" will lift the cam follower slowly to take up the clearance, then the fast opening rate of the valve begins. On the close side of the lobe, the speed of the closing slows down just before the valve touches the seat to prevent battering of the seat, then the clearance gets re-established as the cam lobe transitions to the "base circle" which is ground perfectly round. On a hydraulic cam, the acceleration and deceleration ramps are much shorter since the lifter stays in contact with the lobe all the time.
I don't necessarily agree about wear rates, as the pressure of the lifter on the base circle is minimal, and a properly-preloaded hydraulic lifter eliminates any possibility of the lobe getting battered by an incorrect lash adjustment.
If hydraulic lifters are installed on a solid-lifter cam, the valve begins to lift on the clearance ramps, effectively increasing the lobe duration by a little. That will result in a somewhat rough idle and low intake manifold vacuum at times.
Jerry
