I had a T.Tiger .61 in mine.....6pounds 6 ounces and it was a good performer. With a .91 and a larger prop you might have some ground clearance problems. I had a 12" prop. It has a fairly long fuselage so with some throttle management it should still fly fine. Punching the throttle on TO and not paying attention to the rudder would get mine off heading about 45 degrees.