Solid lifters run a gap so you set the "lash" (which is the space between the rocker arm and the top of the valve) with a feeler gauge. You have to reset them occasionally depending on how many miles you put on it as they will not stay permanently set like a hydraulic lifter. Only the cam specs will limit your rpms. Most hydraulic lifters will not run over 6500 without experiencing valve float. Solid lifters will easily run over 7500 rpm if you have the cam and valve springs for it. Solid lifters are also noisy (a distinctive clatter) compared to hydraulic lifters which make no noise.