OS Max-B21

The OS Engines OS Max-B21 (part number SCH-OS1EG00) is a 3.49cc nitro engine designed for 1/8 scale performance with impressive usability and value. Suited to a wide range of drivers from entry-level to sports users, it delivers a well-balanced mix of smooth speed and responsive power, making it a capable choice across both on-road and off-road racing situations.

Developed from the O.S.SPEED series, the MAX-B21 benefits from race-bred engineering. The outer head, based on the MAX-21XR-B VER.3, has been lightened to enhance performance, while the inner head’s revised combustion chamber shape improves combustion efficiency and low-speed response. The result is strong drivability with more stable idling, reduced tendency to stall, and easier carburettor adjustment.

Suggested Compatibility

• 1/8 nitro off-road and 1/8 GT platforms

What’s Included

• P3 glow plug
• Reducer 6mm (Orange)
• Reducer 7mm (Yellow)
• Exhaust seal ring
• Dust cap set: 3mm / 16mm / 18mm

Key Features

• Easy-to-use performance suitable for entry-level through sports users
• Derived from the O.S.SPEED series for a balanced blend of speed and power
• Lightened outer head (based on MAX-21XR-B VER.3) for improved performance
• Revised inner head combustion chamber for better efficiency and low-speed response
• Stable idling and reduced stalling tendency for easier carburettor tuning
• Capable across both on-road and off-road racing scenarios

Specifications

• Displacement: 3.49cc / 0.213 cu.in.
• Bore: 16.27mm / 0.641in.
• Stroke: 16.80mm / 0.661in.
• Output: 2.6 ps (2.56 hp) at 34,000 r.p.m.
• Practical RPM Range: 4,000–41,000 r.p.m.
• Engine Weight: 361 g / 12.73 oz