The aim is to produce the rising rush of acceleration characteristic of a revvy, normally aspirated engine. Rather than flat-lining, diesel-style, from around 2000rpm, AMG’s new engine generates peak torque at 5200rpm, while nevertheless producing more shove than the old one between 1000-2000rpm, the strongest surge developing from 3000rpm. Overall, said Illenberger, “it produces a more sporty delivery”.
More diesel-like are the 160 bar combustion pressures generated by the new unit, and a lighter yet more robust cylinder block developed to withstand them. It’s of the closed deck variety, creating a crankcase casting more like a part-closed box rather than a semi-open one, with deep, strengthening skirts around the cylinders. The new alloy block is as strong as a diesel engine’s, said Illenberger. The 16-valve cylinder head is also new, a key design challenge being the dispersal of the considerable heat generated.
Larger exhaust valves and valve seats, a redesigned water jacket, oil, water and air chilling for the turbo and separate coolant plumbing for the cylinder head and cylinder block allow more efficient and protective control of under-bonnet temperatures, assisted by electrically controlled water pumps. The head itself features ‘Camtronic’ variable inlet and exhaust valve control and dual injectors per cylinder.
A single piezo-injector per cylinder would be at the upper limit of its fuel volume delivery, said Illenberger, so a second quartet of injectors sits within the inlet manifold tracts to boost delivery under hard acceleration. The Camtronic system enables two camshaft profiles to provide a blend of good fuel economy and heightened throttle response.
The vanes of a sizeable turbocharger run in low-friction roller bearings, an electric wastegate minimising the loss of boost when pressure modulation is required. The turbo now lives between the engine and the front bulkhead, the cylinder head having been turned through 180deg in order to fit the engine beneath the lower bonnet lines of the new models.
The turbo’s new location requires extra cooling, some of this provided by an engine cover shaped to direct fan-generated airflow over it. Illenberger said that the electric water pumps may also function after the engine has been switched off, to cool the block, head and turbo. The more potent ‘S’ version sometimes harnesses the air conditioner for cooling too.
Besides designing an all-new engine, AMG has also developed a more streamlined way to make it. Each engine is still built under the ‘one man, one engine’ approach long used by the company (there are several women hand-assembling these engines too, incidentally) – the methods of electronically recording the sequence of component assembly, and the torque applied to each of its fixings, by each power tool. The new methods save time and improve ergonomics.