I was running a 15/21 turning 8120, went to a 15/22R and now am running 8160-80. I thought the 22 would drop the rpm's by about 100, and pick up some speed. I have an R & D grate, Kanaflex, and the prop. 82 and humid turning 70.8 with both props. Ran 72.6 in the cool with the 21. Confused on the 22R. Why would rpm's go up? It's too high.