Made a change and looking for suggestions. RV-4, o-320, 160hp, Catto 2 blade, Landoll harmonic dampner, standard Saber alum 3/8 crush plate--ran smooth. Was looking for expanded c/g range so installed 1 3/8 by 7" steel Sabre crush plate (with new bolts) and now have a noticeable vibration in the 1100-1500 range, with a slight change at almost all other settings(imagination?) very noticeable with power off for landing.