Engine Masterpieces?

This article was first published in 2002.

DaimlerChrysler has recently shown what are amongst the two best forced induction engines ever made. The Maybach 5.5-litre V12 uses twin turbos and develops over 400kW, while the AMG SL55 uses a screw-type supercharger to help the 5.4 litre V8 on its way to 350kW. Both engines feature water/air intercooling and have a host of interesting technical details.

The Maybach V12

• 405kW (550hp)
• Torque of 900 Newton metres from 2300 rpm
• Twin turbocharger system, twin-spark ignition and three valves per cylinder

At the 72nd Geneva Motor Show, the German luxury car brand Maybach appeared in front of an international audience for the first time in more than sixty years. The time-honoured name "Maybach" is being revived as a separate brand in its own right in the DaimlerChrysler Group.

With its unique roominess, engineering and its exclusive style, the first modern Maybach luxury vehicle follows in the tradition of the legendary Maybach cars of old. The new Maybach will reap the full benefits of leading-edge Mercedes-Benz technology.

In (the northern) Autumn of 2002, Maybach will renew the tradition of its large and spacious saloons with the successor to the legendary "Zeppelin", a luxury car which opens up new dimensions in more ways than one. As with the legendary top-of-the-line model of 1930, a V12 engine will provide the new Maybach with superior power and performance.

With the market debut of its ultra-luxury saloon now just six months away, Maybach has presented the newly developed "Type 12" engine.

Power, smoothness and long life were the key concerns as the development team worked on the new engine. The awesome statistics - 5.5 litres displacement, twin turbochargers, peak output of 405kW (550hp) and peak torque of 900 Newton metres - give the Maybach power and assurance in all situations.

This impressive picture is completed by superb smoothness and outstanding vibrational behaviour. These qualities are inherent design features: the V-angle of 60 degrees balances inertia forces and moments at source, without the need for special balancer shafts.

An advanced twin turbocharger system is responsible for supplying extra air to the V12 unit. With their spontaneous response, the twin turbochargers allow the driver to mobilise the tremendous power of the engine even at lower rpm. The turbines of the twin turbochargers are space-savingly accommodated in the exhaust manifold, a location which also maximises their efficiency. The compressed air flows from the turbochargers through two engine-mounted water-cooled intercoolers, so that its temperature and density are optimised by the time it enters the combustion chamber.

Like the existing six, eight and twelve-cylinder engines of Mercedes-Benz, the Type 12 engine for the new Maybach features twin-spark ignition and three-valve technology.

Three-valve technology - with one exhaust valve and two intake valves per cylinder - speeds catalytic converter warm-up and plays an important part in ensuring that the new Maybach complies with the strict EU4 emissions limits at all times. Two large ceramic catalytic converters are positioned close to the V12 engine.

Alternating-current twin-spark ignition - with ionic current measurement for identifying any misfiring - not only optimises the combustion process, it also reduces the pressure increase in the cylinders, which has a favourable effect on noise. The ignition voltage of 32,000 volts sets a new record.

The engineers who developed the new twelve-cylinder engine opted for a die-cast aluminium crankcase. To minimise noise and vibration, the bottom of the crank assembly consists of an aluminium bedplate incorporating grey cast iron bearing brackets. This gives added rigidity and is also highly effective in combating longitudinal vibration of the engine block. The cylinder head covers are of die-cast magnesium, while the cylinder liners made of a lightweight, low-friction aluminium-silicon alloy.

Maybach V12 Technical Data

Cylinders/arrangement	12/V, 60 degrees
Displacement cc	5513
Bore/stroke mm	82/87
Valves	3 per cylinder
Output kW/hp at rpm	405/550 at 5250
Compression ratio	9.0 : 1
Mixture formation	electronic engine management, 2 intercooled turbochargers
Ignition	battery, 12 V; alternating-current twin-spark ignition with ionic current measurement to identify misfiring cylinders

Mercedes-Benz SL 55 AMG

• Eight-cylinder supercharged engine developing 350kW (476hp)
• 700 Newton metres of torque from 2650 rpm

DaimlerChrysler has recently released the SL 55 AMG, currently the most powerful of all Mercedes passenger cars. Beneath the bonnet lies a newly developed supercharged engine with eight cylinders, developing 350kW (476hp). The powerplant provides its maximum torque of 700 Newton metres from just 2650 rpm - a new record for V8 sports cars. The SL 55 AMG accelerates from 0 to 100 km/h in just 4.7 seconds.

The impressive power development in the eight-cylinder engine is largely down to a newly developed belt-driven supercharger enthroned between the cylinder banks. It works on the principle of a "Lysholm" compressor and achieves about 30 percent more charge pressure than other comparable belt-driven supercharging systems. The compressor screws - Teflon-coated aluminium castings - rotate at over 23,000 rpm (at an engine speed of 6500 rpm) and, in doing so, press 1850 kilograms of air per hour into the engine's combustion chambers. The maximum charge pressure is 0.8 Bar.

The engine management unit calculates whether to use the screw-type compressor depending on the engine speed and load. When required, the electronic system actuates an electromagnetic clutch which drives the compressor by means of a separate poly-V-belt. The advantage of this direct link to the crankshaft is that the supercharger can spontaneously react when the driver presses the accelerator and provide powerful thrust at an engine speed barely above idle.

Besides the compressor, the supercharger module houses an intercooler between the cylinder banks. This charge air cooler operates as an air-to-water heat exchanger, extracting heat from the compressed air and transferring it to the coolant. A pump allows the water to flow through a special low-temperature cooler which is located in the cooling module, between the air-conditioning condenser and the radiator.

The actual water circuit in the 5.5-litre engine works independently of the low-temperature system for the charge air. An electrical suction-type fan uprated to 850 watts takes the greater cooling requirements of the supercharged engine into account.

The oil cooling system is another example of the innovation shown by the AMG engineers: a separate oil cooler is installed in the front apron of the high-performance sports car, from which dissipated air is bled upstream of the cooling module.

The AMG engine's exhaust system has twin pipes throughout (pipe diameter 70mm). It also has two firewall catalytic converters with extremely thin-walled ceramic monoliths as well as two powerful metal catalytic converters on the Roadster's underbody. A total of four lambda probes in front of and behind the firewall catalytic converters establish the exhaust gas composition and forward the data to the engine management unit. This means the SL 55 AMG meets strict EU-4 emissions requirements, even though they are not due to come into force until 2005.

Two centre and rear mufflers with a switchover valve between the two exhaust pipes lend the new AMG Roadster its sporty sound. The entire exhaust system is made of stainless steel and, with its four chromed tailpipes, emphasises the extremely powerful character of this top-of-the-range sports car.

Nearly all the mechanical components in the original SL 500 engine had to be modified when developing the V8 power plant. Components modified included:

• The crankcase, which was adapted by using special transverse screw connections. Measuring 97mm, the bore is the same as in the standard production engine.

• The crankshaft, adapted to the high torque of the supercharged engine using modified bearings and more durable material. The stroke was increased from 84 to 92 millimetres.

• The pistons, which are made of a special material that is extremely resistant to heat and pressure.

• The oil supply, which differs from the V8 engine in the SL 500 in that it has a modified oil sump with oil catch tray and front sump as well as a more powerful oil pump.

• The cylinder head, with optimised intake and exhaust ducts to take account of the higher air flow rate.

• The camshafts, which have longer valve opening times and thus improve charging of the combustion chambers.

• The valve train with a double spring assembly, enabling the rated engine speed to be increased from 5600 to 6100 rpm.

• The engine ECU which performs additional tasks for the AMG engine, such as using electronic maps to activate the compressor clutch.

The new bore/stroke ratio (97 : 92 mm) means the displacement of the AMG engine is now exactly 5439 cc; 473 cc more than the engine in the SL 500.

Mercedes-Benz SL 55 AMG Supercharged V8 Technical Data

Number of cylinders/arrangement	8/V, 3 valves per cylinder
Displacement cc	5439
Bore x Stroke mm	97.0 x 92.0
Rated power kW/hp	350/476 at 6100 rpm
Rated torque Nm	700 at 2650-4500 rpm
Compression ratio	9.0 :1
Mixture formation	HFM microprocessor-controlled injection system

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