I PUT A MAGNUM XLS 46 WITH A MACS HEADER AND TUNER PIPE. I HAVE TRIED PROPS FROM A 10-6 TO A 13-6. THE BEST I HAVE HAD LUCK WITH IS AN APC 12-5. BUT STILL NOT GOOD ENOUGH. THE ENGINE IS TURNING PLENTY OF RPMS. REALLY SURPRIZED BY THIS MAGNUM. HAD 15-20 FLIGHTS AND LOVE THIS PLANE. ANY INPUT WILL BE NICE.