Well I never know they had those way back so it would be interesting to know all of the history of OS. The bottom end of the 11 AX looks close to the 15CVA but i never owned one. I do like how the case is billet and I thing it is the first production engine from O.S. with a billet block. Next payday I will order one or two of the standard 11AX engines to fly and run to see how they perform. I am thinking 8x4 at 15,000