This is the Ultimate MXR v3 Ceramic .21 3‑port Competition Engine “Team Edition” with Ultimate Airmax Air Filter. This engine is manufactured by the prestigious Japanese brand O.S. Engines and is also based on their square‑stroke Speed B21 engine.

Many manufacturers offer pre‑break‑in services performed on test benches with propellers. The problem is that this system works only as a pre‑break‑in, and the engine still requires an on‑track break‑in.

At Ultimate Racing, we wanted to go one step further and offer our customers the possibility of purchasing engines that are fully broken‑in and ready to race with no additional break‑in required. In other words, engines that can be used in the most demanding competitions exactly as you receive them, straight out of the box.

To guarantee quality and ensure that all “Team Edition” engines are broken‑in to the exact same standard, we have developed a fully monitored break‑in bench that controls temperature, RPM, and break‑in time at all times. The entire break‑in process is performed with the engine perfectly lubricated to minimize load and wear on all components, significantly increasing its lifespan.

During each phase of the break‑in, the engine’s resistance torque is also monitored, allowing us to determine the precise moment when the break‑in should be completed. This guarantees that all our “Team Edition” engines are perfectly broken‑in and ready to compete.

Once the break‑in is finished, the engines are disassembled, inspected piece by piece, and reassembled by our racing team, ensuring the highest product quality for our customers.

In addition to the modifications already included in the previous version—such as the crankshaft, backplate, cylinder/piston set, the innovative 6 and 6.5 mm FlowMax venturi, and the crankcase designed to achieve greater power without compromising fuel consumption—the v3 incorporates a new, less sensitive high‑speed needle to make it easier to find the optimal carburetion setting.

With this engine you will enjoy an incredible power curve that delivers outstanding usable power at all times. It provides smooth, linear power at low RPM, making it perform perfectly on bumpy tracks, while also delivering strong mid‑ and high‑RPM power with excellent throttle feel. It is one of the best idling engines on the market.

Main Features:

• Carburetor: Modified OS21J3 carburetor with a redesigned needle holder and high‑speed needle for more stable performance and more precise tuning.
• Crankcase: Same as the v2, where internal fuel flow was improved to achieve extra power and efficiency.
• Filter: All Ultimate MXR v3 engines include a complete Ultimate Airmax filter set.
• Cooling Head: The Ultimate MXR v3 uses the same cooling head as its predecessor. This 8‑fin head has a very low center of gravity and is designed to direct most of the airflow directly toward the glow plug. By cooling the plug, we achieve more stable carburetion and idle.
• Venturi: The MXR features the new 6.5 mm FlowMax venturi. With an innovative design that is longer than standard O.S. venturis and wider at the base, the new geometry improves fluid dynamics, providing extra power and a noticeable improvement in fuel mileage.
• Backplate: The signature red Ultimate backplate is machined from Swiss 7075‑T6 aluminum and features two larger channels that improve the engine’s fuel flow, increasing power and improving consumption.
• Sleeve and Piston: Building on the solid foundation of the MXS, the Ultimate MXR features a newly designed engine group with modified ports to adjust intake and exhaust timing, achieving more power without compromising fuel consumption.
• Bearings: The Ultimate MXR v3 uses an original O.S. ceramic rear bearing and a front steel double‑sealed bearing from Ultimate Racing.

Technical Specifications:

• Displacement: 3.49 cc
• R.P.M. (power): 2.65 PS @ 34,000 rpm
• Stroke: Square 16.40 x 16.40 mm
• Sleeve: 3 + 1 ports
• Rear Bearing: O.S. Ceramic
• Front Bearing: Ultimate Racing Steel
• Crankshaft: 14 mm balanced with two tungsten inserts
• Carburetor: Modified O.S. 21J3 with exclusive needle holder
• Glow Plug: P3 Turbo
• Weight: 345 g