Intense 3D flight with instantaneous power and torque. To generate the desired power in all areas in response to such an ultimate pilot's request, the O.S. SPEED 91HZ-R 3D was created. The specially designed engine head is given a combustion chamber shape that corresponds to 30% nitro fuel, which is common in 3D flights, and of course, it is a machined head that boasts high heat dissipation. Combined with the body of the same colour, it creates a cool appearance with a full-body black anodized finish. The carburettor diameter has also been enlarged to the appropriate size to match the power of 3D flight, and the exhaust port shape of the cylinder has been changed to an optimized design that of course takes into account the output characteristics. In addition, while retaining the DRS equipment, which boasts a stable fuel supply that is not affected by drastic attitude changes, the crankshaft has been redesigned to further improve stability during overflight.