At the end of the intake module, which is cast in AZ91 hp magnesium alloy, there are tumble flaps that assist the combustion process by improving the air/fuel mix under low load conditions. Tumble flaps, fuel injection and ignition, as well as other engine functions, are controlled by Bosch ME 9.7 engine management, which is integrated into the engine design, centrally located above the intake tract. Mercedes worked closely with German supplier Pierburg to achieve fully retractable tumble flaps, helping to achieve higher volumetric flow under high load conditions. Mercedes also employed iron-coated pistons running on aluminum-silicon cylinder liners. The coating is two-pack polymer incorporating iron particles and is a carry-over from the preceding M112 model engine, while the cylinder liners are cast in. By running iron-coated cylinders on aluminum-silicon liners, engineers can reduce oil consumption and friction, while better tolerances lead to improved engine acoustics.
Weight reduction also was achieved in the connecting rods, one of the particular manufacturing challenges identified by Hornikel. "We achieved considerable improvements through further developments of the steel," he explained. "The outcome was a harder material and a trapezoidal design, both of which gave us significant issues to overcome in the manufacturing processes." However, the outcome was clearly worth it, as the weight reduction amounted to 20%.
The development team also focused heavily on acoustics for a specific reduction in engine noise but retaining a sporty exhaust note. This meant a huge amount of development time conducting tests on every one of the 210 engine components. Aside from eliminating obtrusive frequencies generated by individual components, the acoustic experts also paid special attention to the air intake, one result of which was the development of intake ducts in woven nylon. In contrast to the smooth-surfaced plastics normally used in such applications, this material has a sound-absorbing effect and thus significantly reduces intake noise.
Designing it is the easy bit. When new innovations show face, we tend to focus our awe and admiration on the development engineers. But spare a thought for the guys who have to make the thing. For Hornikel's manufacturing people, the raft of innovations brought with it a substantial number of manufacturing challenges.