PRECISION and immediacy. These are the two core ingredients that make a car responsive. And responsiveness, in turn, is a defining characteristic of a good sportscar. Without it, speed and power count for nothing.
Well, that’s the theory. Some performance-car enthusiasts believe that there is no such thing as too much power and that there can be no replacement for displacement.
The Mercedes-Benz SLK55 AMG is undoubtedly an example of the latter theory and brings plenty of firepower to this battle – 78 kW more than its rival, the Porsche Boxster S. The question is whether all that muscle translates into a noticeable performance advantage and, crucially, whether this makes the SLK better to drive. If it doesn’t, what’s the point?
On the other hand, has Porsche done enough with the latest Boxster, perennially (and wrongly) referred to as the “lady’s Porsche”, to elevate it into the echelon of proper sportscars in the minds and hearts of enthusiasts? A classic battle of opposing values ensues.
Design
The compact-roadster segment has often been accused of delivering girly products. Not even a brief association with James Bond, for example, could alter the perception that the original BMW Z3 was more about looking good than going well. Subsequent examples of the SLK and Boxster have struggled to alter this poseur perception. But, thankfully, the latest versions are significantly more macho than their predecessors, with the respective design teams garnering inspiration from supercar siblings, the SLS AMG and Carrera GT.
The current SLK’s shape is familiar and features chunkier, blunter styling than before. For the SLK55 AMG, the focus has been on elevating the levels of visual aggression. There is a new front apron with large air inlets, AMG-specific LED daytime running lights and liberal use of high-gloss black paint. This model also gets bi-xenon headlamps with adaptive light distribution and range adjustment as standard. Other model-specific styling details include unique side sills, a black diffuser with three fins, a rear spoiler and a quartet of chrome-plated exhaust tips. Lightweight 18-inch AMG alloy wheels complete the picture.
Based on impressions gleaned from looking at photographs, you will be excused for thinking the new Boxster looks pretty much the same as before. In the metal, however, it’s a different proposition. For the first time, the Boxster’s design team didn’t have to use the doors of the 911, and the resultant freedom has enabled it to pen a far more distinctive car, mostly because the dimensions have been changed significantly; the wheelbase is 60 mm longer, the front track 40 mm wider, the roofline 13 mm lower and the windscreen has moved 100 mm forward. The side air-inlets are reminiscent of the stunning Carrera GT supercar that was on sale between 2004 and 2007.
The rear, however, has seen the biggest changes. The taillamps are integrated beautifully with the active rear wing. Boxster S models come standard with 19-inch alloy wheels, but our test unit featured 20-inch Carrera S wheels, priced at just under R19 000.
Of course, a major difference between the two vehicles is their roof designs. The Mercedes has a two-piece folding hard-top that stows in 20 seconds. A major negative is that the car has to be stationary to operate the roof. By comparison, the Porsche offers a one-piece folding soft-top that retracts in a lightning-fast nine seconds at speeds of up to 50 km/h. However, once the top is down, the Mercedes starts regaining some lost ground as its cabin is more draught-free and because it offers the standard AirScarf neck/shoulder heating system. In the Boxster, even with an optional wind deflector fitted, the movement of cold air around the neck and elbows is far more noticeable.
Comfort and features
The difference in base price between these two models is misleading because in typical fashion for both marques the AMG is a relatively full-house offering at the standard price, while the Boxster S offers a long list of extras. As tested, these cars were closely matched at around R1 million each.
Nappa leather and aluminium accents dominate the SLK’s cabin. There is an AMG-specific IWC clock on the centre hangdown section, an AMG Performance steering wheel with flattened sections, aluminium shift paddles and an AMG instrument cluster with four instruments.
Our Porsche test unit featured an optional (and very bright) red leather interior (R56 210) and the optional Sport Chrono package (R26 660). Perhaps surprisingly, the majority of the test team found the Boxster the more comfortable car, even when standing still. The new car offers 25 mm more legroom than before and there is a generous amount of adjustment from both the seats and the steering wheel. It’s not that the SLK is uncomfortable, but you do feel like you sit on top of the Benz rather than in it. The Boxster’s high centre console and perfectly placed transmission lever add to the sense of occasion.
Power and performance
On paper, the Boxster S looked set for a hiding of note. Our test figures, however, tell a different story. The Mercedes uses the marque’s normally aspirated 5,5-litre V8 engine that delivers a brawny 310 kW at 6 800 r/min and 540 N.m of torque at 4 500. Mercedes claims a top speed of 250 km/h and a 0-100 km/h time of 4,6 seconds. During our testing procedure, however, the SLK55 could do no better than 5,1 seconds.
By comparison, the Boxster S’s 3,4-litre flat-six engine delivers 232 kW at 6 700 r/min and
360 N.m at 4 500 r/min. The Porsche had no trouble matching its performance claims and sprinted to 100 km/h in 4,68 seconds, aided by the launch-control system included in the Sport Chrono package. A top speed of 277 km/h is claimed.
Even with its power deficit, the Boxster S ran the SLK55 AMG close in overtaking punch. The Mercedes took 1,63 seconds to accelerate from 100 to 120 km/h, with the Porsche only slightly slower at 1,65 seconds. However, the SLK55’s extra grunt started to count as the speeds grew – it was marginally faster to the kilometre mark (23,4 vs. 23,5 seconds).
However, bare numbers constitute but one element of performance motoring. Of perhaps greater importance is the character of an engine and overall drivetrain. Sadly, the SLK55’s woes continued. As one tester explained, “One of the main attractions of any AMG model is its engine sound.” Simply put, the SLK’s V8 failed to rouse the senses, proving disappointingly demure in its aural delivery. The Porsche’s engine, by comparison, is quite a vocal unit, howling gloriously to the red line in each gear.
The respective transmissions fitted play a big role in deter-mining the overall characters of these two cars. The SLK55 uses Mercedes’ automatic 7G-tronic AMG Speedshift Plus transmission that offers C (controlled efficiency), S (sport) and M (manual) modes. The Boxster S has Porsche’s sublime seven-speed dual-clutch (PDK) unit. The difference is vast. In comfort mode, the Mercedes is a perfect boulevard cruiser as the transmission makes full use of the generous torque on offer by simply shifting to as high a gear as possible, as quickly as possible. Punch down on the throttle and the retort is lazy at best. Change to sport mode and things improve, but a quick drive in the Porsche will reveal the SLK’s major shortcoming: responsiveness. Of course, selecting manual mode in the SLK solves one half of the issue, but the other half (tardy throttle response) remains. It doesn’t matter in which mode the Porsche’s transmission is, shifts are executed more rapidly and with more precision. And the Boxster S’s throttle responsiveness is probably unequalled by sportscars costing much more.
On the road
On paper, the AMG looks like the real deal. It features AMG sports suspension with Torque Vectoring Brakes and the AMG direct-steer system that is claimed to improve lateral cornering ability and result in a more agile overall feel. The front suspension features struts with stiffer spring/damper tuning and a more rigid axle. Damping is stiffer and at the rear the more negative camber setup is claimed to result in higher cornering speeds and less body roll. The SLK55 AMG also features three-stage ESP that offers on, sport and off modes. Finally, there are meaty, internally ventilated 360 mm front and 330 mm rear ventilated disc brakes.
It all sounds impressive, but that doesn’t translate into an SLK that’s terribly engaging to drive. The steering offers inconsistent weighting and a vagueness that magnifies the car’s main problem: a lack of responsiveness from all the major dynamic elements.
This Boxster S was fitted with a few options. In addition to the bigger wheels, there were also dynamic transmission mounts (as part of the Sport Chrono package). These mounts change their rigidity and damping characteristics using a magnetisable damper fluid and, according to the prevailing driving conditions, reduce the vibrations that potentially could come from a hard-driven car’s drivetrain. Porsche says they also improve overall stability and precision.
During our evaluation drives, the Boxster S’s precision and finesse garnered rave reviews from all members of the test team.
However, we did not expect the Boxster to also ride better, even on bigger wheels. What we have here is brilliant chassis tuning to create a car that corners with stability and poise, yet one that rides bumps with a fluency that is completely surprising.
Overall, even with the slight slowness of the new electro-mechanical power assistance around the straight-ahead, the Boxster S gives the inert SLK55 a proper hiding in terms of driving fun.
Test Summary
By now you’ve probably realised that this turned out to be a one-sided battle. The Boxster S is more fun to drive, more comfortable, arguably better value for money and significantly more special in the way it fosters an emotional bond with its driver.
Based on what the SLK55 AMG offers on paper, it should’ve been far more convincing. And, while its defeat in terms of dynamic ability and ride refinement can to some extent be forgiven if it had offered something else (a thunderous AMG soundtrack, for example), the fact is that it doesn’t even do that.
If there’s any consolation, losing so convincingly is perhaps a fate that would’ve befallen any rival roadster in this test, as the new Boxster S is not only easily the world’s best compact roadster, but also one of the world’s best sportscars. At any price.
