Check out the MVVS 26c (1.60 cu.in.) gas engine, it should bolt right up to the mount in place of the OS 1.60. This engine will swing a 18x8 wide blade prop at 7600 to 8400 rpm depending on exhaust choice. This works out to about 17 pounds of real-world thrust (over 20 pounds if you beleive ThrustHP) so in a 11 pound airplane 3D will be a possible - on a 16 pound airplane it won't. There are several 40cc engines available if more power is required, but thier suitability depends on the airframe.