Theres as much increase from a solid to a roller as there is from a hydraulic to a solid lift cam. Its one of the best $$ per HP that you can spend. The reason it is, is because the quicker you can close the intake valve, the more hp youll make. On a solid lift cam, if your ramp speed where as quick as a roller your lifters would fly off the cam. Because you can't put the spring pressure on a solid to keep the lifter on the cam, that you can on a roller. If you did, you would have to much heat lifter to cam and lose a lobe. The roller allows you to have more ramp speed and more spring pressure for more Horsepower.