The O.S. 21XR-B Ver.2 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.

Tech specifications:

• Displacement: 3.49 cc
• Bore: 16.27mm
• Stroke: 16.80mm
• Intake ports: 3-port
• Practical RPM range: 4,000 – 40,000 rpm
• Max. power output: 2.42 hp / 34,000 rpm
• Weight: 380Gr