Difference between solid cam and hyd. cam?

The physical differences are as above. The description of where they each would be used IMO is not. The solid cam, due to it's lack of compaction at the beginning of it's lift and faster rates of lift for the same reason, Will make more torque at a lower rpm and more horsepower at a lower rpm point than an ideantical sized hydraulic. Also, perfornance hydraulic cams have certain lifter designs that are just as noisey, and require adjustable rocker arms too...