The new Mercedes-Benz SL: Engine and drive system - The power and the economy

Rich power reserves plus modest fuel consumption – this formula describes the fundamental characteristics of the new SL models. They owe this in part to the two V6 and V8 units from the new generation of BlueDIRECT engines from Mercedes-Benz. As is already the case with the S-Class and the CLS, they now also enable the SL to achieve previously unattained marks for efficiency in its segment. The V8 in the new SL 500 has at its disposal 4663 cubic centimetres of displacement from which it achieves 320 kW (435 hp) – so in spite of having around 0.8 litres less displacement that’s some 12 percent more than its predecessor (285 kW/388 hp). The consumption, meanwhile, falls by up to 22 percent, with the torque increasing at the same time from 530 Nm to 700 Nm – an increase of 32 percent. The V6 engine for the SL 350 has the same displacement as its predecessor – 3499 cubic centimetres – from which it now achieves 225 kW (306 hp). Whilst this means that its output is 7 kW less than the engine in its predecessor (232 kW/315 hp), as the torque simultaneously climbs from 360 Nm to the current figure of 370 Nm, there is no perceptible loss of power – on the contrary, in fact: when accelerating, the new SL 350 even proves superior. Plus the new V6 impresses with its outstanding consumption figures. It is content with 6.8 litres over 100 kilometres, making it almost 30 percent more economical than its predecessor (9.7 l/100 km).

Thanks to the economy of both engines, it has been possible to decrease the volume of the fuel tank from 80 litres to 65 litres. Nevertheless a greater range is available than was the case with the predecessor.

Of a torquey disposition when sprinting

The acceleration times from 0 to 100 km/h go to prove that economy does nothing to dampen torquey spirits. Despite a nominal reduction of 7 kW, the SL 350 covers this sprint in 5.9 seconds, which is three tenths faster than its predecessor. From a standstill the SL 500 races to the 100 km/h mark in 4.6 seconds, making it eight tenths faster than the previous SL 500.

Both engines are exemplary when it comes to in-gear acceleration, too. Proof positive can be found in acceleration from 80 to 120 km/h in 4th gear, for only good figures facilitate fast and safe overtaking on rural roads. 5.5 seconds for the SL 350 and 3.2 seconds for the SL 500 make the new SL’s excellent characteristics in this discipline plain for all to behold.

“The new BlueDIRECT engines in the SL with six and eight cylinders form a unique synthesis of effortlessly superior power delivery, comfort and consuption”, comments Professor Dr Thomas Weber, responsible for corporate research and development at Mercedes-Benz Cars on the Board of Management of Daimler AG. “Both impress in the new SL, delivering refinement of the highest calibre and exemplary environmental acceptability.”

The V8 is in a new league of its own

The new V8 was systematically enhanced on the basis of the very successful predecessor. Mercedes-Benz engineers primarily achieved a high output for a lower displacement by using one turbocharger for each bank of cylinders. The turbochargers were configured to provide high torque even at low engine speeds – compared to the previous engine, the result is an increase of more than 40 percent at 2000 rpm. A superb 700 Nm are available between 1600 and 4750 rpm.

The V6 impresses with its low fuel consumption and high comfort

The new six-cylinder is a naturally aspirated engine. The most striking change between the new V6 unit and its predecessor is a reduction in the V-angle between the cylinder banks from 90 degrees to 60 degrees. This enabled the balancer shaft counteracting primary vibrations to be omitted, and as a result the driver registers an outstanding level of comfort.

Innovative technology makes V6 and V8 engines fit for the future

Both the new V6 and the new V8 from Mercedes-Benz are derived from their predecessors. They have aluminium crankcases, pistons and cylinder heads. The crankshaft, connecting rods and valves are of special forged steel. Practically all the details were, however, newly developed or revised with the aim of achieving more fuel economy, more output and more refinement.

The technology package in the new engine generation includes a number of new developments that are unique in this combination:

- In combination with multi-spark ignition, a further developed, 3rd-generation direct fuel injection system with spray-guided combustion and piezo-electric injectors offers further possibilities for fuel savings – in the V8 by means of an improved, homogeneous combustion process, and in the V6 by a new, stratified combustion process with a considerably extended characteristic map and fuel-efficient lean-burn technology.

- In conjunction with the ECO start/stop function, shift point adjustment and systematic friction-reducing measures, improvements in day-to-day fuel consumption of up to 30 percent are possible.

- Power consumption by ancillary units has been reduced. These include an optimised water pump with 2nd-generation thermal management, a demand-controlled oil pump, a volume-controlled high-pressure fuel pump and an intelligent generator management system.

The key data for the new SL

ECO start/stop function with direct-start

The standard-specification ECO start/stop function operates with starter-supported direct-start. This means that when the engine is switched off, the attitude of the crankshaft is registered by a new crankshaft sensor so that the engine control unit knows the positions of the individual pistons. On restarting, it can then select the cylinder that is in the most suitable position for first ignition. After the starter has briefly turned over the engine, reliable injection, ignition and combustion is immediately possible there.

An additional, demand-controlled electric transmission oil pump supplies the clutches of the automatic transmission with oil pressure prior to starting, so as to enable a swift resumption of the journey after direct starting of the combustion engine via the ECO start/stop function. The starter motor (starter) has also undergone thorough modification: it is now designed to be highly durable, ensuring that it will last a car’s lifetime in continuous urban driving involving frequent auto-starting. In addition, the on-board electrical system is supported by a second battery. As is the case with the starter battery (95 Ah), the “auxiliary battery” (12 Ah) also features maintenance-free AGM technology (AGM = absorbed glass mat).

Intelligent alternator management

Its intelligent alternator management also contributes to the luxury roadster’s sensitive treatment of energy. When the battery is charged to more than 80 percent, the alternator is governed to take load off the engine. The energy required in this operating state is supplied by the battery. If the driver removes their foot from the accelerator pedal or applies the brakes, kinetic energy is recovered and fed to the battery.

Automatic transmission for less consumption and more fun at the wheel

All SL models come with the 7G-TRONIC PLUS automatic transmission as standard. Now in its sixth generation, the multi-ratio automatic transmission was developed by Mercedes-Benz and has been produced since 1960. The new version has once again been thoroughly revised to optimise consumption and comfort compared with its predecessor. The new generation of the torque converter provides an improved dynamic response and reduced noise and vibration levels thanks to a new hydraulic circuit, as well as enhanced dampers and an optimised torque converter housing. The extreme wheel-slip reduction of the torque converter housing, combined with

- larger mechanical damper de-coupling, helps to reduce consumption significantly;

- in addition, the gearshift program in ECO mode has been changed in favour of lower engine rpm at cruising speeds;

- friction-optimised bearings and seals plus a new automatic transmission oil (FE-ATF) with reduced viscosity in conjunction with an optimised additive package.

This results in more driving enjoyment than was the case with the predecessor transmission – and also improved smoothness, not to mention an average of seven percent less consumption (in the NEDC).

What’s more, the increased durability of the new oil also brings with it new oil-change intervals from 50,000 (old) to 125,000 kilometres (new).

DIRECT SELECT gearshift with designer chic and athletic allure

Mercedes-Benz is equipping the new SL with the newly developed DIRECT SELECT gearshift in the centre console – the first vehicle with an automatic transmission to receive this honour. In so doing, the premium brand is establishing a completely new generation of central gearshift for vehicles featuring shift-by-wire (ShW) transmission technology. Its small control lever, reminiscent of a high-calibre joystick, has a driver-oriented position, being installed on the centre console. Its striking design not only underlines the sporty character of the roadster; it also emphasises the high quality of the SL with its exquisite touch and feel, superb ergonomics and unique look.

In addition to an Eco program, the 7G-TRONIC PLUS in the new SL also offers a sports-oriented automatic program. Over and above this, the driver can also select a manual shift program which they operate via the paddles on the steering wheel – which also come as part of the standard specification.

The two automatic programs automatically adjust on a continuous basis in line with the driver’s behaviour. By way of example, if they step on the accelerator pedal more dynamically than before, the shift points automatically move towards more sportiness. In the ECO mode, the shift program is configured differently for lower engine speeds during cruising, thus saving fuel.

In the sportily oriented automatic program, the output is available more spontaneously and it shifts faster. The double-declutching function and active downshifts have been systematically enhanced. During heavy braking, the transmission shifts down considerably earlier, so higher engine speeds make the acceleration which follows easier. The double-declutching function, in which the engine speed is actively raised with an abrupt acceleration, ensures faster and more comfortable downshifting. The concomitant acoustic response underlines a sporty driving style and enhances the unique roadster feel.

In the manual transmission mode controlled using shift paddles on the steering wheel, the engine responds to the throttle over a steeper characteristic pedal curve. Selecting the gear via the steering-wheel gearshift buttons facilitates minimal shift times and emphasises the sporty double declutching. In manual mode, the gear indicator in the instrument cluster moves to a separate section of the colour display, where it shows the seven available gears plus the gear currently selected.