Mercedes-Benz SL55 AMG and SL65 AMG

Technology to the fore in the Mercedes-Benz SL55 and 65 AMGs, with stacks of power, adaptive suspension and electro-hydraulic brakes.

Topping out the Mercedes-Benz SL range are the Mercedes-Benz SL65 AMG and its less powerful brother, the SL55 AMG.

The company poured all its new electronics into all the top SL models, and combines that with massive engines, and the cunning Vario-roof a steel convertible top. The SL65 AMG and SL55 AMG are the most powerful models, and are best able to exploit the innovations.

Monstrous car performance

The SL65 AMG is a monstrous performer with over 600 bhp on tap. It is also pretty expensive. But nowhere near as costly as the SLR McLaren, which sports just a few horsepower more but a lot less weight. The SL600 is much more affordable, but doesn't have that AMG badge, and less power!

These days, AMG is part of Mercedes-Benz, which is why there are so many different AMG models. Maybe too much for product differentiation, if that concerns you. There are so many other SLs that your SL55 AMG might be mistaken in conversation for an S55 AMG, or whatever. Not when they see it though!

All the SL series are limited to 155 mph, but of course you get there much quicker the bigger engine you have only 4.2 seconds to 60 mph for the SL65 AMG, and under 13 seconds to 120 mph. The SL55 needs 4.7 seconds to reach 60 mph.

Shares the looks of the SL600

The SLs are completely new looking Mercedes, which set the style which was souped up for the SLR McLaren, and scaled down for the SLK. Very distinctive, with those twin headlamps aside of the new-look Mercedes grille which as a massive three-pointed star in the middle. The car has a distinct wedge line from the low nose, although the tail doesn’t look too good from some angles a bit weak. The AMG models get different front aprons and larger grilles, and different rear skirts.

But the new shape works; first, it looks great, and second it looks like the luxurious supercar it is. And thirdly, it’s slippery the drag coefficient is only 0.29, which is as good as anything around.

The Vario-roof steel convertible

It’s the power that sets these guys apart, although the engines are basically the same as those in the SLs, but tuned up to turn out proper power. The supercharged 5.4 liter V-8 in the SL55 AMG churns out 500 bhp at 6,000 rpm, and 516 lb ft (700 Nm) torque at 4,000 rpm. Not bad.

Engine enlarged to six litres and given more boost

But if it’s real power you’re after then you’ll be wanting the SL65 AMG powered by the magnificent Mercedes-Benz 6.0 litre V-12. It has three valves per cylinder, but is a 60-degree unit. Like the SL600, a couple of turbochargers boost power, but much more.

First, though, the stroke has been lengthened with the aid of a new crankshaft. Then, to cope with the extra power, the forged pistons are sprayed with oil from jets below. The turbos give 1.5 bar of boost, which is enough to whop the power up to 612 bhp at 5,100 rpm and it can still produce that much a bit higher.

Stupendous torque like a big truck

The torque is just stupendous  what you get from a good diesel with a good petrol engine higher up the speed range. Way down at 1,000 rpm you’ve got 10% more torque than the maximum you’ll ever get from the 5.4 litre engine in the SLK! That’s stunning.

But it gets even more amazing: at 1,500 rpm, at which speed most supercar engines are almost asleep, the V-12 pushes out 612 lb ft (830 Nm) of torque. Is that a lot? Well, the Ford GT, which is no mean performer, and has a 5.5 litre supercharged engine has maximum torque of 500 lb ft, and the SLR McLaren (McLaren won’t like this comparison) can produce no more than 575 lb ft at any speed.

And the SL65 AMG hasn’t finished yet maximum torque is a whopping 737 lb ft (1,000 Nm), and you get it from 2,000 to 4,000 rpm! It’s torque which gives your acceleration, which gets the rear wheels spinning or triggering the limited slip diff. The maximum power of 612 bhp is not to be sneezed at, but that is what gets to the top speed if there wasn’t a limiter.

The torque of this engine is just plain awesome, as is the power output. This engine certainly knocks on the head the notion that superchargers give better low-speed power than turbochargers. True, this is a big engine, and maybe for a four-litre the story might be different, but the balance seems to be shifting toward turbos again.

Five-speed auto only

The plot isn’t so strong when it comes to transmissions. You have to make do with a five-speed automatic box because that was the only thing that could take the torque of the massive V-12. You get a similar box on the SL55 AMG, but it isn’t beefed up so much. Both come with Tip function a manual over-ride.

That automatic will transmit the power plenty quick enough, but the fact is that any normal automatic puts a bit of slush between you and the engine. You just don’t get the same feel of actually driving and controlling that power as you do with a manual or semi-manual.

Wishbones and multi-link suspension

What about the suspension? You get wishbone front suspension for the wheel control you need on a sports car, and Mercedes-Benz admits that this is the best system for wheel control. At the back, you get a multi-link system, which is basically wishbones with some active control of the toe-in as the suspension moves.

Evidently the suspension is set up for under steer with stability control. Nearly all the suspension components are aluminum, and the links are forged for strength. Compared with the SL600, the settings are stiffened up, and the geometry is a little different.

ABC to reduce roll

There are coil springs and dampers at front and rear as usual, but they are aided by Active Body Control (ABC). This system is a breakthrough, reducing roll by about 50% without the need for anti-roll bars. The springs are also softer than normal but the car doesn’t roll as much.

Little hydraulic rams live between the bottom of the spring and the suspension arm and get information from all sorts of sensors, including those used for the stability control. They also measure the weight they are carrying. Yes, all the time.

Computer control and hydraulics

How does it work? When you start off, the computer decides how much weight is being carried on each wheel, and sets the ride height. If you stop and take your luggage out, it adjusts the ride height. When you accelerate, ABC knows what’s going on so it increases the pressure in the hydraulic rams at the back to increase the tension in the springs so they don’t compress much. When you brake suddenly, it is the front rams that push the springs up.

When you corner, the outer hydraulic rams push up on the springs, while the inner ones exert a little less pressure. You can set the suspension to normal or sport mode. Sport mode reduces roll further. On average roll is reduced by 50% compared with the previous model with anti-roll bars when you change lanes, for example.

So you can see that you get a much flatter ride, which reduces the camber and toe-change of the wheels, and makes the car easier to handle. The ride is flatter than on the SL600 owing to the different settings.

However, the ride is not completely flat. Because the hydraulic rams increase the compression of the springs, they can only go so far. If they went as far as needed on really hard cornering, they would compress the springs fully, so the car wouldn’t handle at all. So this is a compromise solution, between cost/energy and performance.

But then there’s stability control

Of course, the stability control works in conjunction with the ABC to give the best cornering power, and is helped by the Senesotronic braking.

Now, braking-by-wire seems a bit spooky, but has been thoroughly tested in fact, to make sure there is always electricity available for it, the SLs have two batteries. The advantages are many. The system can detect an emergency braking situation and act on it from the time it takes you to get your foot from the accelerator to the brake pedal. It can also send signals to the pressurised cylinders at the wheels to wipe the disc with the pads every so often in wet weather.

Sensotronic can also distribute the braking power to the wheels in proportion to how they can use it, rather than acting afterwards with conventional ABS. Also, if you brake during cornering, it puts more braking effort through the outer discs than the inner ones, as this improves cornering power. It is also a more compact system than a normal ABS, but is expensive.

Just to round things off, there’s rack and pinion steering instead of the recirculating ball system on the previous model, which gives much more feel, and is more precise. It wins all round, and is speed sensitive you get more assistance at low speeds.

You also get pretty big wheels and tires to handle all that power: 255/35 R 19 front and 285/30 R 19 rear tyres the SL600 has 18 inch wheels.

The improvements in the brakes are not only in Sensotronic. The SL65 gets massive composite discs, which are lighter and less likely to fade than cast iron discs. The front discs are 15.4 in (390 mm) diameter, and at the rear they are 14 inch (360 mm) diameter.

The SL65 AMG is an amazingly powerful supercar, although too heavy to mix it with the real leaders. It is about 300 lb heavier than the already heavy SL55 AMG, and this despite the use of aluminum and magnesium for several body parts.

A curb weight of 4,648 lb (2,110 kg) puts it up above the Bentley Continental four-seater coupe. Makes you wonder.