The Mercedes-Benz SLK roadster has always been one of the most successful cars in its segment and each

generation has brought a significant innovation to the market. The first generation, launched in 1996, intro-

duced the vario-roof, in simple terms an electrically-operated rooftop. The second generation brought the AIR-

SCARF, a system to blow warm-air around the passenger’s necks with the top down. The SLK one finds in the

showroom today is the third-generation and features the innovative panoramic vario-roof with Magic Sky Control.

Mercedes-Benz sLK 350 3rd-Gen InnovatIon at Core

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New Veh icle MeRCedeS SLK 350

Globally, the SLK series is available with three options for the petrol engine – the SLK 200, SLK 250 and SLK 350. In India though, Mercedes has launched only the SLK 350, brought through the CBU route. It’s fair to assume that not many people would want to buy a two-seater converti-ble (read SLK 200) with about 185 ps for about ` 50 lakh. We drive the SLK 350 and bring to you its first technical review, with details on the new technologies and how they make a difference on the road, along with a comprehensive look at the Magic Sky Control technology.

Design

The design of the third-generation SLK is a big departure from the earlier genera-tions and in the right direction too. The front instantly brings thoughts about the SLS AMG whilst retaining the familiar SLK look for its headlamps. The side pro-file looks true to the SLK heritage with a modern touch to it. With the top down, the car is a visual treat. At the rear too one can find the SLS AMG inspired tail lamp and section curves.

With the new design, Mercedes design-ers addressed the biggest problem histori-cally associated with the SLK – its delicate looks. The new one though, with the design language of the SLS AMG trickling through, looks to be a good-looking road-ster from any angle.

The design is not purely cosmetic and is based on engineering inputs as well to find the right balance between form and func-tion, a critical point for cars these days. The frontal area of the new car is signifi-cantly larger at 1.98 sq m compared to the earlier 1.93 sq m but the design engineers still managed to reduce the coefficient drag (Cd) to 0.30 from the previous generation’s 0.32. In order to keep the weight low, the hood and the doors are now made out of light-weight aluminium. The engine is nice to look at and reflects the attention to detail that has gone into packing the unit within that space.

interiors

The interior cabin of the SLK offers decent space for two adults and is well-laid out to offer comfort and an airy-feel even with

despite the front being larger by 0.05 sqm, the Cd is down by 0.02 to 0.30.

With the roof tucked in, it’s hard to find fault with the design from a side/quarter view.

The SLS AMG-inspired rear provides the roadster with a sporty signature.

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the top closed. The four chrome circular air vents resembling a propeller add a significant amount of sportiness along with sophistication. The steering wheel with a diameter of 375 mm is chunky and easy to hold and adds a lot to the cabin feel. From lock to lock, the steering needs only 2.6 turns, translating into a fairly direct steering.

Seats are very comfortable and offer very good lateral support even when driving in a spirited mode. The seat-belt pretensioner works well and does add to the psychological appeal of safety, while it tightens around the body. It’s hard to find fault with the quality of the knobs or the material in the cabin and every

small bit seems to be of the highest qual-ity. A flowing optical fibre of bright red shade adds a lot to the classy-feel of the cabin at night.

The layout of the controls around the cabin is thoughtfully designed and at no times the driver needs to make an effort to find a button to operate a system once familiar. The cabin reflects the fact that it has been designed around the driver in order to allow for maximum focus on the road.

The left ORVM though is the only dis-traction we could find in the car and its short swivel movement makes it uncom-fortable for drivers with less height. At a comfortable driving position the left mir-

ror does not present the best possible image and leaves a lot of room for blind spots unless one leans back a bit every few seconds.

Panoramic roof – magic sky control

The panoramic vario-roof with Magic Sky Control is the first roof system of its kind in the world and adds significantly to making the SLK cabin one of the best in its class from an aesthetic point of view. The system allows one to choose instantly between a nearly transparent roof and a dark roof shade with the touch of a but-ton placed in the centre overhead console.

In simpler words, the panel of glass houses a liquid which has rectangular particles suspended in it. When one selects the transparent setting an electric current is passed through the panel and the particles in the liquid arrange them-selves in a vertical formation allowing for most of the light to pass through. In the dark setting, the current is in a switched-off state and the particles rearrange them-selves in a horizontal formation and are placed randomly – thereby blocking most of the light.

The panel technology is a patent of Research Frontiers Inc., while the roof panel is supplied by Pilkington Automo-tive. The panel containing the chemical fluid is manufactured by Hitachi Chemical of Japan. The technology might be a first for the automotive industry but has been in use in the aviation and architectural sectors.

The system is not designed for aes-thetic purposes only and aids in maintain-ing lower cabin temperatures and filtering harmful UV rays. Mercedes claims to have tested the effectiveness of the system through a star pyranometer in Death Val-ley. Pyranometer is a device used to meas-ure the intensity of exposure to sunlight. During the test with the roof down, the thermal load from solar rays varied between 1,000 and 1,100 W/ sq m. With the roof up in transparent mode, the read-ings declined to a low 200 W/ sq m, and with the dark mode the readings surpris-ingly lowered to an average of about 45 W/ sq m.

The system also helps reduce CO2

emissions, since lower cabin temperatures

Supportive and comfortable seats make the SLK 350 a great car for long-distance cruising.

The cabin layout is excellent and every control is easy to reach and operate.

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New Veh icle MeRCedeS SLK 350

directly translate into lesser loads for the HVAC compressor and hence lower emis-sions. The new roof system’s frame is made from magnesium to lower weight by 6 kg over the previous generation. The boot’s volume is 335 l and is good enough for holding luggage of two people for a short trip.

Powertrain

The new SLK is powered by a 3.5 l engine producing 305 bhp and a torque of 370 Nm @ 3,500 rpm. The V6 engine is a completely new unit with BlueEFFI-CIENCY technologies in order to lower emissions and increase fuel-efficiency. The engine features the third-generation of direct injection system, piezo injectors and multi-spark ignition. Mercedes claims the direct injection system, also known as BlueDIRECT to be their most efficient ever. The BlueDIRECT, through in-engine

improvements, alone enhances fuel-effi-ciency by a claimed 20 percent.

We noticed that vibration levels are extremely hard to notice whether tackling the rush hour traffic of New Delhi or doing speeds of over 200 kmph on smooth roads. This is primarily due to the angle of the V6 engine, which is just 60 degrees and hence allows for the balancer shaft for primary vibrations to be done away with.

The third-generation direct injection system now operates with a pressure of up to 200 bar and varies depending upon the engine’s operating characteristics. Newly-developed piezo-electric injectors enable up to five injections per stroke, thereby enabling for a better optimised fuel-air mixture. In combination with multi-spark ignition, the direct injection system enhances fuel-efficiency through a new stratified combustion system and lean-burn technology. Adding to the effi-ciency is the reduction of power con-

sumption by ancillary units through usage of a new thermal management system, volume-controlled fuel pump and a gener-ator management system.

Lightweight construction and friction reduction was of utmost importance in order to push the efficiency envelope fur-ther. To meet desired results, the crank-case, pistons and cylinder heads are made of aluminium while the crankshaft, con-necting rods and valves are made out of forged steel.

The engineers used the basic architec-ture of the previous engine to modify the variable, hydraulic vane-type camshaft adjusters for the intake and exhaust sides. This allowed for the adjusters to sport a larger adjustment range of 40 degrees in reference with the crankshaft. Technical advancements made it possible to achieve 35 % greater speed for the adjusters and operability at a low-oil pressure of even 0.4 bar. Despite this, the engineers were able to reduce the size and weight of the component to an extent that designers were able to reduce the installation space on the longitudinal and transversal axis of the engine by about 15 mm.

Transmission duties are handled by a 7G-TRONIC PLUS seven-speed automatic transmission featuring three driving modes – Eco, Drive & Sport. The trans-mission shifts happen seamlessly but aren’t very quick in the Eco & Drive modes. While the Sport mode does quicken up the response, the overall shift timings left a bit to be desired for. Given its segment and positioning the transmis-sion doesn’t need to change at a pace

The lighter vario-roof takes under 20 seconds to complete a transition.

The powertrain strikes a good balance between performance and efficiency. downsizing a lot of components made it possible to fit the engine in this bay.

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The third-generation dI system combines multiple new technologies/developments to increase the fuel-efficiency.

anywhere close to a high-performance sports car but could shift a little quicker in the Sports mode, at least.

hanDling & Dynamics

The SLK handles well over bumpy sur-faces and drives through potholes and speed-breakers with comfortable ease. Ride quality at all speeds and surfaces is pliant and soft without much body-roll. The SLK features a lowered suspension with stiffer springs and continuously adjustable damping. The adjustable damping electronically monitors the damper situation and adjusts them to suit

the surface with a response time of about 10 milliseconds.

The car doesn’t show any nervous-ness, while changing lanes even at speeds of over 180 kph and is comfortable with taking sweeping corners as well. Acute turns and sharp steering inputs though bring about a bit of body-roll and signs of unsettled behaviour. One can’t complain about this fact though since the car isn’t engineered to perform like a sports car. But as a long distance cruiser, the SLK 350 does a good job.

One thing, which we found to hamper the driving experience, is the steering feel. While the steering is very direct and accu-rate, its feedback isn’t very appreciable

and the artificially-induced over-weighted feel doesn’t help either. The hydraulic set-up though is engineered to save fuel inter-estingly by minimising the throughflow pressure, when driving straight and reduc-ing the energy requirement.

technical rounD-uP

Mercedes has mostly introduced new technologies to the market with its new-generation models and especially with the SLK, every generation brought about a major innovation to the roadster class. The SLK 350 does justice to this history and has introduced a major innovation in the form of its electro-chromic roof and a new-generation of direct injection system.

The SLK 350 is a lifestyle car for some-one looking at the best balance between luxury, style and performance. These technologies also ensure that despite a 3.5 l V6 engine, the CO

2 emissions are restricted to 167 g/km.

A thoughtful feature adding to conven-ience is the ‘Brake Hold’ function, which allows the driver to engage the brakes by swiftly pressing the brake pedal twice and thereby not having to slot into park mode, a boon in traffic. The brakes automatically disengage when the throttle is applied.

Technically, the car is sound and eve-rything seems to work the way it was intended to. Small touches such as flaps behind the seats that can be rotated to allow air passage to reduce turbulence in the cabin is one of the many small engi-neering touches one can find in the car. At XX lakh, ex-showroom, Delhi, the SLK might sound a bit expensive but is well-positioned against the competition and one of the most technically advanced too. As we mentioned about the energy-saving steering earlier, there are many compo-nents in the SLK designed to be more effi-cient and that is an indication that IC engines still haven’t reached their ceiling of efficiency.

The 7G-TRONIC PLUS unit doesn’t maximise the performance potential of the engine, but does so in terms of efficiency. n

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