Impeller sizes. Can one of you guys explain, in general, larger impeller sizes. I have heard of AA, 3A and 4A. Diameters of 9, 9 and 1/4,9 and 1/2 inches. Do these relate to the AA,3A and 4A? I am hoping to put more power to the pump soon. Hoping to dyno in 2 weeks. Where do high helix impellers fit into the mix? Thanks, DEL.