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First Look: SLK 350

A new look and a bigger engine makes it a pursang sports car

Greg N. Brown
Jun 22, 2004 SHARE
0407_01z+Mercedes_SLK_350+Front_Side_And_Rear_Side_View Photo 1/6   |   First Look: SLK 350

In less time than it took to twist the steering wheel or even think about braking, the SLK 350 was hard upon the loose pack of cyclists, who were flinging themselves downslope, their brightly colored livery forming an image of giant tropical birds, tires hissing as though a hundred wings were slicing through the air.

The impending disaster wasn't entirely unexpected. The mountain roads of Mallorca were humming with biciclestas, and I'd already been spooked by their sudden appearances around blind corners. This time, to keep from tattooing the trailing cyclist's tail feathers with a three-pointed star, I thrust both legs forward, responding with muscle memory, no time for reasoning. I jammed the brake and clutch pedals to the floor, and the high-rev roar of the SLK's new V6 fell off like the echoed blast of a huge baritone sax. The car decelerated straight and true, and I escaped tagging the clueless cyclist--though I did come close enough to admire the intricate stitching of his uniform's logos (and an equally admirable set of haunches).

My co-pilot made another rude observation about these gaggles of two-wheelers, who would swing back and forth in front of us like flushed quail, just fast enough that we couldn't get a good shot off...I mean, make a safe passing move on the paved goat paths that passed for roads through the rugged mountains. These disruptions in the SLK's flight path (think falcon's dive interrupted by a flock of sparrows) were particularly aggravating, because the rural byways on the Spanish island are wonderful, winding up and over knife-edged ridges that spill groves of olive trees off their steep flanks. Dozens of switchbacks, each with unique entry and exit points, dip in and out of forest shadow, and every time you expect a straight, it's instead been cleverly kinked, as though to give the locals extra slalom practice.

0407_02z+Mercedes_SLK_350+Front_Side_View Photo 2/6   |   First Look: SLK 350

The roads are lined with miles of beautifully crafted stone walls, whose beauty reminds the driver to be respectful of the available asphalt, which is narrow and often falls off sharply into ditches designed to funnel water away from the road and, regrettably, to flip over the cars which blunder into them. The climate is mild, the pavement is smooth as vintage Mallorcan vino, and the consequences of an "off" are dire enough to test both a car's athleticism and a driver's confidence in his own skills.

The myriad threats to car and driver, however, just added spice to a delectable and not uncommon side effect of travel to the Mediterranean--falling in love, in this case with the new SLK 350.

I hadn't expected it. Early in day, as the redesigned roadster sat in the murk of a foggy morning, this newest silver arrow displayed stimulating styling, but I wondered if the promise would be an empty one, that the grilles, vanes and spoilers adorning the aggressively wedge-shaped profile would be more accessory than technical necessity.

I recalled the first SLK. It had a lot of promise, too, when it was born, but for me it never became more than a shallow personality in a family of overachievers, a clever but colorless aspirer to a club that considers having fun the prime requisite of membership.

0407_03z+Mercedes_SLK_350+Seat Photo 3/6   |   First Look: SLK 350

That's not to say the first-generation SLK was a failure. To the contrary--since its introduction in the fall of 1996, over 308,000 of the two-seaters were sold worldwide, making it by far the number-one sales performer in its segment. The car just never made me want to find a deserted winding road. I would never have traded in the Porsche Boxster S for a car from the other company in Stuttgart. Now, I'm not so sure.

Once underway, and after the new SLK and I began our tactile relationship, it was clear there was considerable substance under the car's new bodywork. And then, after I'd attacked the drive's first set of corners, I realized that Mercedes-Benz had come up with a very special car. Later, after an extended blast along a black ribbon of pavement that seemed glued to a cliff that sank straight into the sea, I concluded that we could live together happily. Its power and poise would have knocked me off my feet if I hadn't been sitting in the strikingly restyled cockpit. It was like dancing with someone who knows how to both lead and follow. My pleasure centers were jolted, and I felt the dawning of a new lust warming the soft air of that spring day in the Mediterranean.

Earlier, morning dew played a staccato beat with the pavement's coefficient of friction, making the traction control work hard, but the ESP electronics tamed potential "moments" into almost imperceptible adjustments of the chassis. It was as though my dancing partner were constantly improvising intricate steps to keep our balance intact, while all I had to do was keep from doing something stupid. Which I did just once, when I punched the traction control button off to see just how slippery...whoa, Nelly! It was like frying an eel in a non-stick pan and provided a startling glimpse of the new V6's personality. The 258 lb-ft of torque comes on quickly and strongly, beginning its wide plateau at 2400 rpm and extending to 5000 rpm. The 268 bhp, peaking at 6000 rpm, are willingly delivered by the free-revving 3498cc V6, and keeping the car's electronic handling aids fully operative does little to diminish the sporting nature of the handling. More telling of the engine's effect on the new car's character is the power to weight ratio, which has been improved by 20% over the current SLK 320. And though the SLK 350 weighs in at 3,231 lb, heavier than the Boxster S (2,,911 lb) and Z4 (3,020 lb), it feels to be more than a match for the Porsche and BMW in acceleration. Mercedes states the 350 will pull the car from 0 to 60 mph in 5.5 sec., about 0.3 sec. faster than a Boxster S, almost a half second faster than the Z4 and a full second better than the 320.

Indeed, the SLK 350 is improved in every aspect, and larger in every dimension, compared to the outgoing model. This isn't unexpected from a company as capable as Mercedes-Benz, but it is big news that the company has drastically changed the car's essential dynamic from GT to pursang sports car. (It's almost as though it's taking out the frustration of a dismal showing in Formula One on its street car competitors.)

0407_04z+Mercedes_SLK_350+Front_Interior_Dash Photo 4/6   |   First Look: SLK 350

Longer than the 320 by 2.8 in., wider by 3.0 in., taller by 1.3 in. and with a 1.2-in.-wider wheelbase, the SLK 350 also has considerably more trunk volume (6.6 cu ft with roof opened vs. 4.8 cu ft) thanks to a new pivoting rear window in the slick Vario-roof, which now opens and closes more quickly (22 sec.). In re-checking the car's specs after I drove it, I noted the more rigid chassis, strengthened by 19% in bending resistance and 46% in torsional rigidity over its predecessor (roof down). This stiffer structure was augmented with all the goodies needed to enhance a driver's connection to the road: bigger brakes, tighter steering, heftier running gear, quicker shift throws and a more willing throttle. Add a new front axle and major revisions to bearings, bushings and links in the independent rear suspension, and the SLK 350 has all the earmarks of an AMG-massaged Mercedes.

The front discs, increased from 11.8 in. to 13.0 in., are now perforated as well as ventilated and are gripped by four-piston fixed calipers in place of single-piston floating units. The rear solid discs were enlarged from 10.9- to 11.4 in.; retained are dual-piston fixed calipers.

As I discovered during the cockfighting between my SLK and the hordes of cyclists, these are the best Mercedes brakes I've ever felt. There's none of that electronic disconnect which compromises some of it cars' braking systems, and the surety delivered by their application makes late and threshold braking an important aspect of the 350's appeal to serious drivers.

Massive improvement is also found in the steering, a rack-and-pinion unit replacing the previous recirculating-ball setup. It hands the reins to the driver like no other Mercedes and is a far cry from those old days of oversized steering wheels and overly damped racks. Whereas the SLK 320's steering muffled driver awareness of what the front wheels were up to, the new system makes a direct connection from the hands to the tires and then on to the road. The engineers would point out that positioning the lighter rack ahead of the front wheel center contributes to better chassis balance and increased safety, but the driver will experience only an unprecedented response to the twist of his or her hands on the wheel.

The precision of the new rack was particularly impressive as I weaved along the unknown Mallorcan roads. The car seemed like it had local knowledge as it flowed smoothly through sudden transitions, and it conquered unexpected corner radii as though it had an on-board Cray computer charting the optimum line.

0407_05z+Mercedes_SLK_350+Rear_View Photo 5/6   |   First Look: SLK 350

Once the province of BMW, Mercedes now has caught on to this handling thing. If the big Benzes are wonders of stately balance, and the SLs are the epitomes of sporting luxury, this small sports car represents the union of those qualities. Fear of road-kill cyclist appearing on the local police blotter and attention to the unforgiving rock walls tempered my desire to drive the SLK as quickly as, say, a Boxster (with which I am extremely familiar), but there's no denying the SLK is a superb handler. It slices into corners like fine German steel and tracks through the bends with complete communication between nose and tail. Weight transfer is easily felt and corrective moves responded to with efficient directness--no secondary oscillations in the suspension when the car transitions through an S-bend, no excessive brake dive, and no unsettling squat when the V6 is asked to run free.

I'd occasionally fall in behind a fortunate local, who had to get nowhere slowly, enjoying a long life, free from stress, healthy as a tub of yogurt from his Mediterranean diet...and then I began to appreciate the SLK's supple ride, very unlike its predecessor's proclivity to hop over road imperfections. This new suspension soaks it all up, shrugging aside cracks, holes and humps while it waits for the next curvy road to get tough again.

In cruise mode, if you squint your eyes, it's easy to think you're in the bigger of Mercedes' roadsters. A total restyling of the gauge panel, seats and supporting aesthetic touches resulted in a decidedly upper-class look and feel to the accommodations. Hand-fitted leather upholstery will be among a long list of standard fitment for U.S. cars, including a nine-speaker sound system and in-dash CD player, Tele Aid, an automatic antitheft alarm system and a mini spare backing up the 17-in. 10-spoke alloys on U.S.-bound SLKs. The staggered tire setup consists of 225/45R17s in front and 245/40R17s in back.

One option is worth singling out for its uniqueness--the AIRSCARF system, which pumps warm air through the seats' backrests, onto the necks of the occupants. At high speed its effect was negligible, but when creeping along it helped keep a late afternoon chill off my neck.

Mercedes-Benz continues to churn out one terrific car after another, blanketing the world market with a wider spectrum of vehicles than has ever been offered by a single manufacturer. This car-for-everyone strategy would be a dismal failure for a lesser entity than Mercedes' mighty machine, and a stunning stream of superb vehicles argues in favor of this proliferation of new models. The SLK re-emerges into a market full of good cars at a time when two-seaters might be considered a bit frivolous, but the typical buyer, according to Mercedes marketing, will be a tad younger (49) than the 320 buyer, a bit less affluent ($120,000), and will more likely be an unmarried male.

We won't get the 2.0-liter version in the U.S., and sales of the SLK 350 begin this September with prices starting in the mid $40,000s. Pursang performance freaks may want to wait for the SLK55 AMG, due in showrooms in November. We'll save details of this monster until we drive it, but suffice to say its power-to-weight ratio puts the 320 to shame.

Though, really, the V6-powered SLK has nothing to be ashamed about. Its connection to the heart and soul of Mercedes' technical acumen is clearly felt in every mile of driving. High-tech touches, both seen and unseen abound. For instance, the excellent new seats have backrests made of magnesium for its lightness and high strength. And transmission choice is either a six-speed manual or a new seven-speed automatic gearbox. I'd opt for the stick, as its linkage and throws and feel are so improved that it's actually fun to shift this car.

There are all the expected safety systems in place, including new head/thorax airbags in addition to the front adaptive airbags and two-stage belt limiters. Steel tubes in the A-pillars and the two roll-over bars also are in place, which, thankfully, I never needed. Everything stayed sunny-side up in sunny Mallorca, a great place to drive (and bike).

Details: 3.5L V6
Less is more for the new SLK and C-Class

By: Elaine Catton

0407_06z+Mercedes_SLK_350+Engine_Cutaway Photo 6/6   |   First Look: SLK 350

Be it weight, noise, fuel consumption or emissions, Mercedes-Benz's new 3.5-liter 272-bhp V6 has less of it. Highlights of the unit include variable intake and exhaust camshaft adjustment, a world first for a V6 engine, a two-stage intake manifold, tumble flaps in the intake ducts and an intelligent heat management system.

Bringing weight down, however, is not just a matter of clever design. New manufacturing technology also has an important role to play. "The camshafts, for example, are assembled using an internal pressure-forming method (IHU) with pressed-on lobes," explained Thomas Hornikel, overall project manager for New Generation V engines.

The lightweight camshaft construction was also a factor in reducing the loads necessary for the new infinitely variable timing mechanism. The camshafts are controlled by electro-hydraulically operated vane-type adjusters. They are located at the front ends of the shafts and are controlled by four integral hydraulic valves. The intake camshafts are driven by a duplex chain, while the exhaust shafts are moved directly by the intake shafts via a braced pair of gearwheels. The system was a joint development project between INA and DaimlerChrysler's Berlin engine facility.

The new valve control system enables continuously variable valve adjustment up to 40 degrees for the very first time in a V6 application. Aside from the main benefit of permitting optimum timing, it provides the engine with the added facility of exhaust gas recirculation, a key factor in improving fuel consumption. The camshafts are adjusted so that the exhaust valves remain open for a short time as the intake valves are open, while the partial vacuum in the intake manifold draws in the exhaust gases.

Mercedes-Benz also designed new flow-optimized intake ducts for the best possible throughput in accordance with engine load. From approximately 3500 rpm, the flaps are open, thus providing the shortest possible intake path and upping engine output. By closing the flaps under partial load, the route to the cylinders is lengthened, thus creating pressure waves that improve torque generated at lower engine speeds. The result is 225 lb-ft (305Nm) of torque, or 87% of maximum torque, available from as low down as 1500 rpm.

At the end of the intake module, which is cast in AZ91 hp magnesium alloy, there are tumble flaps that assist the combustion process by improving the air/fuel mix under low load conditions. Tumble flaps, fuel injection and ignition, as well as other engine functions, are controlled by Bosch ME 9.7 engine management, which is integrated into the engine design, centrally located above the intake tract. Mercedes worked closely with German supplier Pierburg to achieve fully retractable tumble flaps, helping to achieve higher volumetric flow under high load conditions. Mercedes also employed iron-coated pistons running on aluminum-silicon cylinder liners. The coating is two-pack polymer incorporating iron particles and is a carry-over from the preceding M112 model engine, while the cylinder liners are cast in. By running iron-coated cylinders on aluminum-silicon liners, engineers can reduce oil consumption and friction, while better tolerances lead to improved engine acoustics.

Weight reduction also was achieved in the connecting rods, one of the particular manufacturing challenges identified by Hornikel. "We achieved considerable improvements through further developments of the steel," he explained. "The outcome was a harder material and a trapezoidal design, both of which gave us significant issues to overcome in the manufacturing processes." However, the outcome was clearly worth it, as the weight reduction amounted to 20%.

The development team also focused heavily on acoustics for a specific reduction in engine noise but retaining a sporty exhaust note. This meant a huge amount of development time conducting tests on every one of the 210 engine components. Aside from eliminating obtrusive frequencies generated by individual components, the acoustic experts also paid special attention to the air intake, one result of which was the development of intake ducts in woven nylon. In contrast to the smooth-surfaced plastics normally used in such applications, this material has a sound-absorbing effect and thus significantly reduces intake noise.

Designing it is the easy bit .When new innovations show face, we tend to focus our awe and admiration on the development engineers. But spare a thought for the guys who have to make the thing. For Hornikel's manufacturing people, the raft of innovations brought with it a substantial number of manufacturing challenges.

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By Greg N. Brown
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