Roos are very flexible aircrafts when it comes to powering them. I have seem them fly with 12, 17 and 28+ lb. turbines. Aside from the .9 to 1 AMA rule, consider that the engine mount sits fairly high on the plane and I have seen a couple of them make uncontrollable hard turns on take-off rolls when throttle is advanced to max too quickly. I know the insatiable speed freaks out there will opt for the 20+ lb. turbines.