Needs to be braced up with balsa as Piroflip says. It's not a torque problem, it's gyroscopic forces ripping the motor mount out. Try this, hold the plane with the nose pointed up. Now, put it at wide open throttle and swing the tail back and forth fairly fast like a pendulum. and feel the forces that are working against it swinging. That force is being put on your firewall and the glue is the only thing holding it. You need to transfer that load back to the sides of the fuselage with bracing.