The drive delivers maximum torque of 515 lb-ft (700 Nm), which is already available from the extremely low engine speed of 1,200 rpm and catapults the rear wheel drive Mercedes S 400 d from 0-60 mph in around 5.3 seconds. Boasting 335 hp (250 kW), it is the most powerful series production diesel engine in the Mercedes-Benz range, yet still delivers impressive standard fuel consumption of 45 mpg US (54 mpg UK). The slightly less powerful inline six-cylinder turbodiesel with the designation S 350 d generates 281 hp (210 kW). This is accompanied by 442 lb-ft (600 Nm) of torque, which is also available from 1,200 to 3.200 rpm. Delivering 46 mpg US (55 mpg UK) of diesel, this model is slightly more frugal.
Optimized for response time and efficiency
The spontaneous response and impressive performance figures delivered by the two engines are primarily thanks to the regulated, two-stage exhaust gas turbocharging, which also makes an important contribution to the high fuel efficiency. BorgWarner supplies an R2S® system for the two versions of the OM 656. This ensures an optimum torque band and also permits high exhaust gas recirculation rates under full load conditions.
The system comprises of two turbochargers arranged in series, whereby the more compact high pressure turbo is equipped with the latest VTG technology (variable turbine geometry). The larger waste gate turbocharger for low-pressure duties has a so-called “ported shroud”, which distributes the air stream evenly over the vanes of the impeller wheel. At low revs, the high-pressure stage secures extremely fast boost pressure build-up. As the engine speed increases, a bypass valve then opens and feeds virtually the entire exhaust gas stream to the low-pressure stage, which in turn facilitates high boost pressures at maximum efficiency. Thanks to electrical actuation, the R2S® system from BorgWarner adapts very quickly to changing operating conditions. It shortens response times, improves pickup, and reduces pollutant emissions.
Innovative cast solution
The newly developed R2S® turbocharging system is the first two-stage solution available in the market that is equipped with a cast steel casing. The electrical actuator, as well as the bearing and impeller casings are water-cooled. A new and particularly compact design also saves space in the engine compartment and makes it easier for the engineers at Mercedes-Benz to overcome the challenges in terms of packaging – such as limited installation space and high temperatures.
With the innovative eBooster® electrically operated impeller, as well as the new R2S® turbocharging system, the turbocharger pioneer is once again demonstrating that it is more than qualified to work as a partner on sophisticated, high-end engine development projects.