The O.S. 21XR-B Ver.3 club-level nitro GT and off-road engine. The power plant targets club level drivers and it features the 21J3 3-needle carburettor with 7mm and 8mm venturi inserts.
Displacement: 3.49 cc
Intake ports: 3-port
Practical RPM range: 4,000 – 40,000 rpm
Max. power output: 2.42 hp / 34,000 rpm