Four-pot for S-Class

The downsizing wave is about to get its biggest rider yet, with Mercedes-Benz sources confirming the German luxury marquee will launch its first four-cylinder S-Class limousine next year.

The default choice for prestige car buyers, heads of state and the odd black marketeer, the S-Class has ruled supreme at the head of the luxury car world for nearly six decades, but it's never deigned to consider a humble four-cylinder engine before. But retiring S-Class program Vice President, Hans Multhaurt, let slip in France this week that increasing environmental awareness among European fleet buyers will force Mercedes to fit its twin-turbo-diesel four-cylinder unit to the limo next year.

"I suggested it, to put a four cylinder engine into the S-Class," the engineer admitted.

"It's not going to be a new engine, but we have had to do some work on the OM651 diesel we already have [in the C-Class and the E-Class]. We had to do a lot of work to it to make it more civilized, though."

That "work" included working towards a target power output of 150kW, around 40 shy of the current S350 BlueTec V6 turbodiesel. And by next year, the OM651 2.0-litre four cylinder engine will have had its balancer shafts removed, with internal vibration-cancelling duties instead being entrusted to a crankshaft with 10kg more weight spread along its length.

"We did a lot of work decoupling the engine from the chassis for NVH [noise, vibration and harshness] reasons. We had to take some of the ugly out of it," Multhaurt admitted.

"It's difficult to decouple it completely for smoothness, because the water cooling systems are fixed to the car. It will get two-stage turbocharging and a dual-mass flywheel as well, and it should be a permanent feature of the S-Class.

"With the way fleets and big companies are being run, they focus on fleet consumption and corporate emissions -- that's why this four-cylinder is under development," Multhaurt confirmed.