Power and hi-tech stuff have always been the hallmark of the
Mercedes-Benz SL steel-roof convertible supercars, but now power is up, and there are new gearboxes. It is the Mercedes-Benz SL63 AMG which is the sportier, whereas the SL65 AMG goes for sheer power – 600 bhp!
There are minor changes to distinguish the cars from the previous ones, with black painted grilles, larger air intakes below the grille and side skirts The front end changes the look of the car quite a lot. At the rear, the diffuser is more obvious, while there are twin oval exhaust pipes each side.
Very fast acceleration
The result of these changes is that the SL63 AMG now reaches 60 mph in about 4.5 seconds, and the SL65 AMGV-12 takes about 4.1 seconds, which is very quick especially for such a heavy car.
Despite developing the V-12 engine to a high level, Mercedes-Benz AMG engineers seem to prefer the more compact new V-8 for all-out performance. The new engine is similar in many respects to a racing unit, with hard coated cylinder bores to reduce weight of the aluminum block, and valve gear designed to high revs – to about 7,200 rpm.
Output from the 5.4 liter V-8 is 517 bhp (386 kW) at 6,800 rpm, with 464 lb ft (630 Nm) at 5,200 rpm, making this a very sporty unit that thrives on high revs. A specific output of 82 bhp per liter is high for such a large engine.
New semi-automatic gearbox
What really sets the SL63 apart is a new version of the Mercedes-Benz 7-speed automatic box which now gets true manual operation, and is called Speedshift MCT.
They have thrown away the energy-sapping torque converter and replaced it with a wet-plate clutch. There is the same hydraulic control system for gear shifting as before, but the take-off from rest is much faster than before as are the gearshifts.
When shifts are made, double declutching is employed to speed up shifts and ensure complete synchronisation. As this is automated, it takes placed very fast.
As a result, shifting in Manual mode is very fast at 100 milliseconds, which is 50 per cent faster than in Comfort, with Sport mode coming in between.
Gearshifts in 100 milliseconds
Shifts are either by the gear lever or paddles - Mercedes-Benz does not seem able to give up the gear lever. The driver gets four modes, which are controlled by a rotary switch near the gear lever. The three main modes are Comfort, Sports and Manual, which have different shift points and different shift speeds.
The fourth mode is Race Start which optimises the power for the fastest possible take-off. It will remain in operation till the top speed is reached if desired.
To handle the extra power, the Active Body Control, which limits roll, has been modified, so that roll is reduced even further in the Sport setting. The Comfort setting gives a softer ride.
Stiffer suspension, very little roll
Springs and dampers are stiffer than before, as are the mounts, while larger bearings are used. Also new is a stability control with three settings, something that is now to be expected on supercars and other sporty cars. The settings are either On, Off or Sport, which enables the driver to push the car further before the system intervenes. Sounds good.
The Mercedes-Benz SL63 rides on 19-inch wheels with 255/35 R 19 front and 285/30 R 19 rear tires. To give plenty of stopping power, six-pot calipers work on 14.2-inch (360 mm) diameter carbon-ceramic front brakes while four-pot calipers work on 330 mm ventilated and perforated cast iron discs at the rear.
SL65 AMG V-12
How does the
Mercedes-Benz SL65 AMG stack up? Well, it is the winner hands down in effortless power and smoothness, because the 6.0 liter V-12 has twin turbos. The result is a massive power output of 603 bhp (450kW) from 4,750 to 5,100 rpm, while torque is a whopping 737 lb ft (1,000 Nm) of torque anywhere between 2,000 and 4,000 rpm, which will give the car stunning acceleration at any speed. This is actually the same as the previous model.
The character of the engine is completely different from the SL63 AMG, which needs to be revved hard to get the maximum power, whereas this V-12 will waft the car along in a more relaxed manner – but with one big sting in the tail at full throttle.
Owing to the massive amount of torque, this engine is too powerful for the Speedshift MCT box, and so it makes do with a five-speed automatic, which has three modes of operation. There is also a limited slip differential, which will be highly necessary in some conditions.
Bigger carbon-ceramic brakes
The SL65 AMG gets bigger brakes than the SL63 AMG, owing to it power and extra weight, with carbon-ceramic discs all round – 15.3-inch (390 mm) at the front and 14.2-inch (360 mm) diameter at the rear. Should be big enough.
Although there is nothing radical in these Mercedes-Benz SL supercars, the new gearbox will set some competitors thinking, and the performance of both is doubtless stunning. As before, they are very heavy. though.
To check out the technology in these cars, such as the suspension which reduces roll, go to:
Mercedes-Benz SL65 AMG and
Mercedes-Benz SL600 AMG.
