OS Speed B2105 Combo Set

The OS Engines OS Speed B2105 Combo Set (SCH-OS1EK01) advances the renowned B21 series into its fifth generation. Developed for tough off-road racing, this .21-class nitro engine focuses on delivering an advantage in harsh conditions with smooth, linear power and dependable drivability. The combo includes a matched pipe, providing a convenient foundation for competitive setups.

Engine refinements include a redesigned cylinder liner and crankshaft to achieve a more progressive throttle feel, while a lighter outer head further improves drivability across a wide range of track conditions. The result is a refined power unit that aims for consistent performance when the racing gets demanding.

Key Features

• Fifth-generation B21 series .21-class off-road racing engine
• Redesigned cylinder liner and crankshaft for smooth, linear power delivery
• Lighter outer head to enhance drivability
• Supplied as a combo with pipe included
• Engineered for consistent performance in demanding off-road scenarios

Specifications

• Displacement: 3.49 cc (0.213 cu in)
• Bore: 16.27 mm (0.641 in)
• Stroke: 16.80 mm (0.661 in)
• Output: 2.68 ps / 2.64 hp at 34,000 rpm
• Practical rpm range: 4,000–42,000 rpm
• Engine weight: 348 g (12.28 oz)

Standard Accessories

• Glow plug T-P3
• Reducer φ6Ⅱ
• Reducer φ6.5Ⅱ
• Exhaust seal ring
• Dust cap set 12-30 (φ3, φ16, φ18)

With its evolved internals and lighter head design, the OS Speed B2105 Combo Set offers a controlled, linear response geared for competitive off-road racing. The inclusion of the pipe and the listed accessories makes it a compelling choice for racers seeking a refined .21-class powerplant from OS Engines.