The "OM656" Inline Six-Cylinder Clean Diesel Engine

The new inline six-cylinder clean diesel engine, the "OM656," powers four models: the "S 400 d," the all-wheel-drive "S 400 d 4MATIC," and their long-wheelbase variants, the "S 400 d Long" and "S 400 d 4MATIC Long," which feature a 13cm stretch in length to expand rear-seat space.

This engine, part of a modular concept that shares basic design principles with the "M256" inline six-cylinder gasoline engine found in models like the "S 450," boasts the highest output among the company's clean diesel engines, with 340 ps and 700 Nm of torque. It reportedly delivers smooth acceleration with minimal vibration and exceptional quietness. Furthermore, it complies with RDE (Real Driving Emissions) regulations implemented in Europe, offering high environmental performance.

The OM656 features a compact design with a cylinder pitch of 90mm and 8mm spacing between cylinders. The cylinder block is made of aluminum for weight reduction, while the pistons are steel. Over 40% of friction is reduced by using materials with different thermal expansion rates, and the cylinder walls are treated with NANOSLIDE, a low-friction coating of steel carbon material. A two-stage turbocharger, with variable turbine geometry on the smaller turbine, is said to provide strong torque across the entire rev range.



Environmentally, the engine utilizes a common-rail direct injection system with piezo injectors operating at up to 2,500 bar, and a "multi-way exhaust gas recirculation (EGR)" system combining cooled high-pressure and low-pressure EGR. This optimizes combustion and reduces NOx before aftertreatment. The variable valve lift system "CAMTRONIC" on the exhaust side allows a portion of the exhaust gas to be returned to the combustion chamber during the intake stroke when cold, enabling the exhaust gas purification system to reach its efficient operating temperature more quickly, thus contributing to cleaner emissions.

Furthermore, mounting the purification system closer to the engine prevents a drop in purification efficiency. Exhaust gases from the turbocharger first pass through an oxidation catalytic converter, then have AdBlue aqueous solution added. Downstream, the sDPF (DPF with SCR Coating) collects particulate matter and reduces nitrogen oxides, before the final SCR catalytic converter treats the remaining nitrogen oxides.

Pricing starts at 11.16 million yen for the S400d, 11.60 million yen for the S400d 4MATIC, 14.61 million yen for the S400d Long, and 15.05 million yen for the S400d 4MATIC Long. Deliveries for the two 4MATIC models are expected around October of this year, with the two 400d models scheduled for around November.