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This is the 3 port .21 Off-Road Ultimate M3X Competition Engine. Like the M3T, it’s a 3 transfers OS based engine, with the same configuration and power than its predecessor.

Unlike the M3T, the M3X incorporate the following parts:

- High precision steel rear bearing made in Japan.

- Balanced crankshaft with tungsten weight and silicone filling.


The M3X, like the M3T, is a square stroke, specifically designed for maximum power, performance and tuneability. With this engine you will have a great and super smooth linear power from low to high R.P.M.Produced with the guaranteed OS quality, the M3X is a cheaper option with the same power and performance than its predecessor, the M3T.



The cooling head has been redesigned by Modelix. It’s not as low as the B2102 lower profile but it’s lighter so it keeps the center of gravity as low as the B2102 but improving its performance on very high temperatures. It’s the same head as the M3T and M3S engines.


The Ultimate M3X engine comes with the same carburetor than the M3S and M3T engines where high speed needle holder has been redesigned for a better refrigeration of the fuel flow into the carburetor, lowering the temp of the carb, and as a consequence it’s more stable with a great idle stability, improves fuel mileage and overall engine performace.

Besides this, the uniball joint of the carb slide has also been modified with two stoppers instead of one. With this new modified design, you can easier adjust the angle of the uniball joint without having to disassemble the engine.

This carb offers a higher accuracy tuning, a very interesting advantage to experienced drivers.


The backplate is CNC machined and made of 7075-T6 Swiss Aluminum. The reason of making it with this material is to make it harder than the original and reduce the conrod-backplate friction increasing the life of the conrod and improving engine efficiency and performance.

Thanks to its design, you can remove the backplate without damaging the conrod even when it is on its lower position (PMI). The lateral grooves allow to easily remove the backplate without having to use any tool that can damage it.


The M3X crankshaft has been designed by the O.S team of engineers to ensure an optimum flow of fuel thanks to the aerodynamic design and the silicone filling. It is balanced with a tungsten weight in order to increase the inertia to rotation.


In line with the high quality and performance of this engine, its two high precision made in Japan bearings ensure high idle stability, longer life and low friction at high temperatures.


The engine is supplied with a 6.5mm aluminium venturi.


The sleeve with 3 inlet port and an exhaust port guarantee a low fuel consumption with a very high but smooth and linear power.

Both, the sleeve and piston are made from a high strength aluminium bar to improve its durability.



Displacement: 3,46 cc

Power Output: 2.75 PS/2.71 hp @ 34.000rpm

Practical Range RPM:  4.000-44.000

Bore x Stroke: 16,40x16,40

Sleeve: 3 + 1 ports

Rear Ball Bearing: steel

Front Ball Bearing: steel

Crankshaft: 14 mm

Carburetor: Aluminum w/ insulator gasket

Glow plug: P3 Turbo

Exhaust Position: rear

Weight:  345g

Fuel type: 25% nitro.

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