europe only! not the OP’s 2015 S550. story does not say if THIS fancy motor has eco-start also?
The biggest news in the S-Class engine world isn’t news at all for the United States. A new S500 model is being launched in Europe and elsewhere in the world, powered by an all-new M256 engine sporting a cutting edge 48-volt electrical system that allows it to combine mild hybrid functions with starter-generator functions through a sandwiched electrical drive unit. This, in turn, allows Mercedes to convert all of the external accessories from their archaic belt-drive to more efficient, and more controllable, electric-driven accessories. Getting rid of the accessories on the front of the engine also decreases its length, making it easier to package the M256’s inline six-cylinder layout. Electric-drive accessories on the M256 include the engine’s water pump and the air conditioning compressor, but also an electric supercharger that fills the 3.0-liter inline six-cylinder’s torque gaps. The result? A more efficient, smarter engine that’s capable of 429 hp and 383 lb-ft of torque in S500 trim. Those figures net the M256-powered S500 a 0 to 60 mph time of roughly 4.7 seconds. Unfortunately, we won’t get this powertrain in America — or at least there are no plans for it as yet.