Mercedes-Benz SLK More Sporty And Powerful
The original SLK set a trend with its metal convertible roof, even though the idea had been pioneered for a short period by Honda on the small CR-X. Mercedes turned an interesting idea into a hit, which made the SLK unique. Needless to say it is an important feature on the new car standard what's more and it has been improved.
But the big question about the new SLK is whether it performs on the straight and round the bends. There are three cars in the new range, and all good performers in a straight line anyway. To give the top model the sort of performance you normally get from an SL, it has a V-8 engine, which pushes it up to 60 mph in 4.9 seconds near supercar time. The V-6, which is likely to be the most popular model, gets to 60 in 5.6 seconds. That's pretty quick, too.
With the new three-piece grille, which includes the famous three-legged emblem in the middle, the SLK gets a completely new look, with a strong family resemblance to the larger SLs and SLR McLaren.
It's a cool looking car with a strong wedge line from the curved nose which has almost triangular lamps instead of the linked twin ovals of some other models. The coach roof is also nicely curved, and of course is the now famous and brilliant vario roof, which opens and closes in just 22 seconds. Overall, pretty neat, and with a Cd of 0.32 which is a little better than the old car.
To shoehorn the V-8 in, the body had to be widened quite a bit; the car is 2.5 inches wider and three inches longer than the old one. So far so good. Now for the super power trains.
V-8 from the SL55, and a new V6 engine
Under the hood of the SLK 55 AMG is the 5.4 liter V-8 used in the SL 55 AMG, but with a little less power- 360 bhp at 5,750 rpm. This is a really high-torque engine which produces 376 lb ft (510 Nm) at 4,000 rpm to give masses of acceleration at any speed. It is an all-aluminium engine, and should be capable of accelerating the car to 180 mph or so, but it is limited to 155 mph; so is the less powerful V-6.
However, because the SLK is a small car for a 5.4 liter engine, acceleration all through the range is really rapid it takes only 17.5 seconds to reach 125 mph.
To ensure durability, oil is sprayed onto the undersides of the pistons in the V-8, and good mid-range power is provided by a combination of variable valve timing, and dual-length intake system features found on the smaller SLK engines as well. In fact, all the models are bristling with technology; some you'll want, and some you won't.
New on the SLK is the 7G-Tronic seven-speed automatic transmission, which gives better acceleration and fuel consumption than the old five-speed job. It is standard on the SLK 55 AMG and optional on the SLK 350.
You can shift manually or let the box do its thing. Manual shifts are performed by pressing buttons on the steering wheel these are rather small for fast shifting, though.
This isn't your usual automatic; it has some neat ideas of its own. So when you decide you need to shift down quickly with the kick down, the box doesn't just shift down one gear and then decide to shift once again. Instead it shifts down the lot in one go maybe from seventh to fifth or even third if necessary. Really cool.
Innovative V-6 with tumble valves
The new 3.5 liter V-6 is the most innovative of the engines, with an aluminum block and head. To save weight, silicon aluminum liners are used instead of cast iron, and the pistons are coated with iron, as on the previous model.
Now, though, there are four valves per cylinder, and it has an interesting way of getting good combustion at light loads, such as when cruising along the freeway. Variable valve timing, in which the camshaft is rotated relative to the sprocket to advance or retard opening, and a two-pipe intake manifold ensure good mid-range torque as well as maximum power. Flaps in the intake manifold are opened or closed to make the pipes long for low speeds, and shorter for high speeds.
Tumble valves to give good low-speed performance
New to Mercedes are 'tumble valves' in the intake ports. When operating, these are inclined in the ports so that the mixture has to pass through a narrow gap at low speed. This causes tumble in the cylinders, which is good for combustion.
At higher speeds, the valves are pivoted back out of the way so the engine can develop full power. The use of these valves allows the use of big ports suitable for high power without them, either the low-speed running would be poor, or the ports would need to be smaller, restricting maximum power. This is one of the many new tricks engine designers are learning to liberate more power, and more fun.
272 bhp from the V-6
This all seems to work very well, as the engine generates 272 bhp at 6,000 rpm, with maximum torque of 258 lb ft (350 Nm) all the way from 2,500 to 4,000 rpm. This engine will give excellent performance over almost the entire speed range that's what you expect from a V-6. Mind you, the engine doesn't quite match the power and torque of the Nissan 350Z mill, although the Mercedes-Benz unit does have more low-speed torque, and 77 bhp per liter is not bad at all.
163 bhp supercharged job for the cheapest SLK
The smallest engine in the SLK range is just 1.8 liters, despite the '200' name tag. It is called a Twin pulse engine, and is typical of modern engines with its four valves per cylinder, but it also has variable valve timing and a pair of Lanchester balancer to reduce vibrations. Lanchester was a famous British engineer who invented the idea, among many others.
The system consists of a pair of shafts with balance weights that rotate in opposite directions at twice engine speed, and thus take out the vibrations you normally get with a four.
To give the engine enough power it has a belt-driven supercharger and intercooler. Power output is 163 bhp at 5,500 rpm, with maximum torque of 176 lb ft (240 Nm) at 3,000-4,000 rpm. Not bad engine performance, except that the car is now heavier than the previous model, so it takes 7.9 seconds to get to 60 mph.
Stronger, wider body
The new body is a natural progression of the old one, with strength and stiffness increased, and more safety features. To reduce weight, an ultra-thin magnesium casting separates the fuel tank from the trunk now a bit larger and there are two aluminum panels at the rear of the cockpit.
In search of more responsive steering, Mercedes-Benz has opted for a rack and pinion not before time, one might say and has retained the multi-link rear suspension which helps reduce dive on braking and squat on acceleration.
Struts replace front wishbones
Surprisingly, the wishbone front suspension the best thing for a sporty car has been replaced by struts. With the need to find room for the big V-8 and more crumple zones at the front, there presumably wasn't room to get in wishbones that would have given the geometry the engineers wanted.
Therefore they opted for a strut layout because there was room to get a good linkage in. Mercedes also says that they wanted to reduce out of balance effects of the wheels on the steering, and that struts are better for this.
Composite discs on the V-8
Braking is conventional, although the V-8 gets Mercedes' latest technology composite discs for reduced stopping distance and less weight. Of course, ABS is standard, as is traction control, brake assist which ensures that the brakes are applied with maximum pressure during emergencies. ESP, which reduces the tendency of the car to under steer or over steer if the driver corners too fast, is also standard.
All in all, the new Mercedes-Benz SLK range offers something for all sporty drivers. The body is more rigid, there's more power than before, and better braking. The handling is also more sporty, and should be able to handle the power of the 5.4 liter V-8, particularly since the AMG version has been planned at the outset as a different model with many different components.
There is a slight weight penalty of 55 lb on the SLK 200 Kompressor, which will result in similar performance to the old car, as the power output is hardly increased. On the SLK 350, the extra torque of the larger engine will take the extra 140 lb into its stride. The new Mercedes-Benz SLK 350 could well be the ideal car for anyone wanting a really compact but ultra-powerful sports car.