Mercedes-AMG is putting the AMG 4.0-ltr V8 biturbo engine at the sporting heart of the new Mercedes-AMG GT. With peak power of up to 375kW (510 hp) and maximum torque of up to 650Nm the new engine follows a V8 tradition that started in 1967 with the M100 in the 300SEL 6.8 AMG racing car.
Two turbochargers are mounted on inside in a V configuration, often referred to a ‘hot inside V’, the benefits of which include a compact engine design, optimum response and low exhaust gas emissions.
Dry sump lubrication allows the engine to be installed lower, which moves the centre of gravity closer to the road to form the basis for high lateral acceleration.
Merc claim that the combination of hot inside V and dry sump lubrication is a world first for a sports car engine and that a dry weight of 209kg also makes it the lightest engine in its competitive segment.
With a displacement of 3982 cc, in terms of technology the V8 is closely related to the AMG 2.0-litre turbo engine in the A 45 AMG, CLA 45 AMG and GLA 45 AMG. Both AMG engines have the same bore/stroke ratio and use third-generation direct petrol injection with piezo injectors.
The aluminium crankcase is produced using sand casting technology and features a closed deck design that increases strength whilst keeping the weight as low as possible, and enables high injection pressures of up to 130 bar. The cylinder bore surfaces feature nanoslide technology that is claimed to make them twice as hard as conventional cast-iron linings.
Nanoslide was developed by Daimler and has been used in over 200,000 engines and is also being deployed in the new Mercedes F1 V6 turbo engine. ‘Spectacle honing’ is another measure to reduce friction and fuel consumption. In this complex process, the cylinder liners receive their mechanical surface treatment when already bolted in place.
A jig resembling spectacles is bolted to the crankcase in place of the cylinder head mounted later. Any cylinder warpage that might occur during final assembly is taken into account or eliminated as the cylinder liners are honed.
Dry sump lubrication eliminates the need for a conventional oil pan and allows the engine to be dropped 55 millimetres and ensures direct oil extraction from the crankcases for optimal engine lubrication, even at high speeds on bends.
Dry sump lubrication deploys a suction pump, a pressure pump and an external oil tank with a capacity of 12 litres. The oil suction pump extracts oil directly from the crankcases, cylinder heads and valve body assembly and delivers it to the external oil tank at a pump output of up to 250 litres per minute.
The lubricant remains there for just five seconds before being pumped back around the high-performance engine. On-demand control of the pressure oil pump takes into account the engine rpm, temperature and load characteristics stored by the control unit.
The cylinder heads are made of a zirconium alloy and four overhead camshafts control a total of 32 valves. A combination of biturbo charging and direct petrol injection, with spray-guided combustion, increases thermodynamic efficiency reducing fuel consumption and exhaust gas emissions. Piezo injectors spray the fuel at high pressure into eight combustion chambers, multiple injection occurs on-demand and the delivery of fuel is electronically controlled and fully variable for a fuel pressure between 100 and 200 bar.
Electronically controlled blow-off valves ensure a very immediate and direct response. The maximum charge pressure is 1.2 bar; the turbochargers have a maximum speed of 186,000 revolutions per minute. For combustion purposes, 2.3 times more oxygen atoms are pressed into the turbocharged engine, as would be the case in a naturally aspirated engine.
The two firewall catalytic converters in thin-walled ceramic material positioned down from the exhaust gas turbochargers respond very quickly due to their close-coupled configuration. In conjunction with two metal, underfloor catalytic converters, the AMG 4.0-ltr V8 delivers effective emission control.
There is an exhaust flap on either side of the rear silencer, which is actuated variably on a logic-controlled basis depending on the transmission mode, driver’s power requirement and the engine speed. At low loads and engine rpm the flaps remain closed. This causes the exhaust gases to cover a longer distance and flow through an additional damping element so that the engine sound is pleasantly subdued and irritating frequencies are effectively suppressed.
When the driver accelerates, the flaps progressively open so that although some of the exhaust gases cover the longer, acoustically dampened distance, most travel the shorter distance. Under full load at higher engine speeds, both flaps are fully opened, thus allowing the occupants to enjoy the powerful sound typical of an AMG V8.
Other sophisticated solutions deployed on the engine’s periphery include:
- Separate cooling-air flow for the exhaust gas turbochargers under high thermal load;
- Active engine mounts for excellent lateral dynamics with no loss of comfort;
- Auxiliary units efficiently powered by two short, low-friction belts with four grooves. Intelligent positioning of auxiliary units virtually neutralises belt forces on the crankshaft;
- Two-mass flywheel with centrifugal pendulum prevents torsional vibration on the driveline for a smooth ride;
- ECO start/stop function and alternator management to save fuel.