 Mercedes’ M278 4.6-litre twin-turbocharged V8. Click image to enlarge |
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Stuttgart, Germany – Consumer demands, good environmental practices, and ever tightening fuel consumption regulations – both here and in the European Union – are of particular concern to premium brand automakers like Mercedes-Benz, whose model lines are largely comprised of heavier, more powerful cars.
While Mercedes makes a range of passenger car engines that varies from the diminutive Smart Fortwo’s 800-cc 3-cylinder turbo diesel (a motor no longer offered in North America), all the way up to the 603 horsepower, 6.0-litre twin turbo V12 found in the Maybach 62 S, its core products, particularly in the North American market, are driven primarily by V6 and V8 gasoline engines. Efficiency gains in those motor lines are therefore critically important.
 Prof. Dr. Leopold Mikulic (Vice President Program Management and Development Passenger Car Engines and Powertrain, left), and Gerhard Doll (Project Manager Development Gasoline Engines V6 and V6 Mercedes_Benz Cars, right), with the new 4.6-litre M278 V8 engine. Click image to enlarge |
Mercedes’ current V6 and V8 engine families received their last substantial redesign in 2004, when the previous single overhead cam/three-valve per cylinder head design (with twin spark plugs) was jettisoned in favour of a more efficient double overhead cam/four-valve layout. The switch to individual camshafts for intake and exhaust actuation meant that each set of valves could now be variably timed relative to one another, with commensurate benefits in economy, emissions, and power delivery.
Technology marches on relentlessly, and Mercedes has further improved its engineering; both its V6 and closely related V8 engines have been considerably reworked.
While the 3.5-litre displacement remains, the most immediately noticeable change between the current “M272” V6 engine and the new “M276” V6 that will replace it over the next few years is that the motor’s V-angle has gone from the 90 degrees it presently shares with the V8 to a narrower 60 degree offset.
This seemingly minor change is actually a profound one, because not only does it require significant retooling and major structural design modifications, it also has the costly potential to reduce how many components can be shared between the six and eight cylinder motors, both of which are to be produced together, as before, in the company’s Bad Cannstatt facility.
The benefits however are two-fold, and as a result of some clever planning, outweigh the drawbacks.
 Mercedes’ M278 4.6-litre twin-turbocharged V8. Click image to enlarge |
Most immediately obvious to drivers should be smoothness. Because of the particular frequency and timing of a six cylinder’s combustion events, 90 degree V6 engines have an inherent imbalance that creates undesirable vibrations and resonances; conditions that are not present when that angle is changed to a V6-optimal 60 degrees.
Given the present M272’s occasionally coarse demeanour, particularly at elevated rpm levels or under load, overall refinement should be appreciably better.
Since an engine-driven balance shaft is no longer required to counteract those unwanted forces, its weight, complexity, and frictional losses can all be eliminated. Less drag equates to more power, and – just as importantly – reduced fuel consumption.
As such, initial output figures peg the new V6 at a class-competitive 306 hp and 273 lb-ft of torque, up from 272 hp and 258 lb-ft, while attaining a predicted 24 per cent reduction in fuel consumption in the European cycle.
The newly revised V8, dubbed “M278”, has been reduced in displacement from the current M273’s typical 5.5 litres to 4.6 litres.
