Link to the website: https://www.hrcdistribution.com/rc/articles.php?id_article=1000031474

The new Ultimate MXR v3 Ceramic .21 Competition Engine has arrived. Developed in cooperation with O.S. Engines and based on the proven Speed B21 platform, the MXR v3 combines outstanding drivability, efficiency and race-winning performance.

Expected arrival: 15 June 2026

Product Description

This is the Ultimate MXR v3 Ceramic .21 Competition Engine with Ultimate Airmax Air Filter. This engine is manufactured by the prestigious Japanese brand O.S. Engines and is based on their square-stroke Speed B21 engine.

In addition to the modifications already featured in the previous version—such as the crankshaft, backplate, cylinder/piston set, the innovative 6 and 6.5mm FlowMax venturi, and the crankcase designed for higher power without compromising fuel consumption—the v3 incorporates a new, less sensitive high-speed needle to make finding the optimal tuning point easier.

With this engine, you will have an incredible power curve that provides spectacular usable power at all times. It delivers linear and smooth power at low RPM, making it perform perfectly on bumpy tracks, while simultaneously providing great power at mid and high RPM with excellent feel. It is one of the engines with the best idle on the market.

Main Features

Carburetor

Modified OS21J3 high-speed needle and needle holder to achieve more stable operation and precise tuning.

Crankcase

Same as the v2, where the crankcase was designed to improve internal fuel flow, resulting in extra power and efficiency.

Filter

All Ultimate MXR v3 engines include a complete Ultimate Airmax filter set.

Cooling Head

The Ultimate MXR v3 features 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 tuning and idling.

Venturi

The MXR features the new 6.5mm 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 notable improvement in engine runtime.

Backplate

The signature red Ultimate backplate is CNC-machined from 7075-T6 Swiss aluminum and incorporates two larger channels that improve fuel flow, increasing power and improving fuel consumption.

Cylinder and Piston

Building on the solid MXS base, the Ultimate MXR features a redesigned cylinder/piston set where the ports have been modified to vary intake and exhaust timing, achieving more power without compromising fuel consumption.

Bearings

The Ultimate MXR v3 uses an original O.S. Engines ceramic rear bearing and an Ultimate Racing steel-ball front bearing with double seals.

Technical Specifications

Available Models

• UR3401-MR3
• UR3401-MR3C1
• UR3401-MR3C2
• UR3401-MR3X

Available from 15 June 2026 at HRC Distribution.