Marine thermal engine O.S. 21XZ-M21D Carburetor 3.49 cm3

The O.S. MAX-21XZ-M engine: O.S. technology at the service of competition

The O.S. MAX-21XZ-M represents several decades of experience from O.S. Engines in the development of high-performance nitro engines.

Designed for demanding pilots, it is intended for high-speed radio-controlled boats seeking maximum power while maintaining excellent reliability.

Derived directly from the 21XZ-R car engine, which has won multiple international competitions, it receives specific adaptations for model boating including a water-cooled cylinder head, a large-diameter O.S. 21D carburetor, and a crankshaft optimized for the high loads encountered in RC boats.

With a displacement of 3.49 cm³, the engine delivers up to 2.75 PS at 33,000 rpm and can operate up to 45,000 rpm, making it one of the most powerful 3.5 cm³ glow engines of its generation.

A mechanism designed for very high performance

The MAX-21XZ-M uses a modern architecture designed to optimize engine efficiency.

Its sleeve features seven transfers and three exhaust ports, significantly improving cylinder filling and available power at high RPM.

The crankshaft undergoes meticulous balancing thanks to silicone filling combined with two tungsten counterweights, reducing vibrations and enhancing engine flexibility across the entire operating range.

The lightweight piston, reinforced connecting rod, and materials used by O.S. Engines also contribute to the reputation of reliability of this engine.

The O.S. 21D carburetor

One of the main advantages of the MAX-21XZ-M is its renowned 21D carburetor.

Specially developed for competition engines, it offers:

• very high air flow;
• excellent acceleration response;
• precise tuning;
• perfect high-speed fuel delivery.

It is perfectly suited for competition fuels containing up to 30% nitromethane, allowing the engine's full potential to be unleashed.

Specific design for RC boats

Unlike engines intended for radio-controlled cars, this Marine version receives several specific features:

• high-efficiency water-cooled cylinder head;
• adjustable carburetor based on hull installation;
• crankshaft adapted for marine transmissions;
• designed for extended full-load use.

This architecture ensures excellent thermal stability even during long periods of full-power navigation.

Technical specifications

• Displacement: 3.49 cm³
• Bore: 16.27 mm
• Stroke: 16.80 mm
• Power: 2.75 PS at 33,000 rpm
• Operating range: 4,000 to 45,000 rpm
• Type: 2-stroke glow engine
• Cooling: water-cooled
• Carburetor: O.S. 21D large diameter
• Recommended glow plug: O.S. RP7 Turbo
• Weight: 307.5 g
• Usage: high-speed and competition radio-controlled boats

Why choose the O.S. MAX-21XZ-M?

• Japanese manufacturing by O.S. Engines
• Derived from the famous 21XZ-R competition engine
• High-performance O.S. 21D carburetor
• Very high power for a 3.5 cm³ displacement
• Excellent high-speed performance
• Recognized reliability in competition
• Ideal for monohulls, hydroplanes, and other fast RC boats

The O.S. MAX-21XZ-M with 21D carburetor is today one of the most powerful glow marine engines ever produced by O.S. Engines in the 3.5 cm³ category.

Its modern design, high performance, and Japanese manufacturing quality make it an excellent choice for both competition and high-end RC boat restoration.