From European Car:
Text and photos by: Ian Kuah
The old adage, “too much power is just enough” is certainly true when it comes to many supercars. But when you say that the 571 hp packed under the long bonnet of the SLS AMG is not enough, most people would look at you as if you were crazy.
In reality, it is not so much that 571 hp is not enough, but more the fact that AMG’s M159 four-cam, 6.2-liter V8 powerhouse thrives on revs, doing its most inspirational work at the top end. Thanks to its generous displacement, the low-speed grunt of this big motor is impressive in relation to say the 4.0-liter V8 in an M3. But it still lacks muscle when compared to AMG’s own next-generation M157 5.5-liter, bi-turbo V8.
So what do you do if you really want to boost the output of the SLS AMG motor? The good news is that the engine bay of the SLS is quite large compared to that of the other cars in the Mercedes range fitted with this same basic motor, so finding the space to fit twin turbos or a supercharger is not a big issue.
“We considered both forms of forced aspiration, but chose to go supercharged as it gives us the progressive power and torque from just off idle we were looking for, with less heat and variance per chassis than turbocharging,” explained Michael Weiss, co-founder and owner of Weistec.
The core of Weistec’s SLS 750 system is a Lysholm twin-screw supercharger of 2.3L displacement, mated to the cylinder heads by a digitally designed, high-flow, cast-aluminum T6-hardened intake manifold.
Intake air reaches the supercharger via a Y-shaped cast supercharger inlet fed by twin intake tubes and two throttle bodies mounted in factory locations allowing OEM installation. The shape of these beautifully cast pieces was developed using computer modeling to optimize the airflow velocity seen at the supercharger’s inlet. These components are also cast from aluminum and branded “Weistec SLS.”
I was very taken by the in-house-developed belt-drive system that sits prominently on the nose of the supercharger. A supercharger is driven off the engine crankshaft and alters its boost pressure in a relationship with engine speed controlled by the diameter of its pulley. Thus, boost pressure is raised through increasing rotational speed by using a smaller pulley.
Once that relationship is fixed, its effectiveness can also be improved if the system does not allow for any slippage. Realizing this, Weistec developed what they term a CMDP (Constant Mu, Delta Pressure) drive that maintains constant friction in the cog drive, and hence boost pressure in the system.
The Weistec CMDP system, which is the subject of a Weistec patent, neatly achieves a change in supercharger gearing, and hence boost pressure, through a change of its cog pulleys. This is a far less troublesome route than swapping out the pulley on the supercharger nose, which would entail changing the length of the engine-driven belt.
Intake charge temperature is kept down by Weistec’s proprietary water-cooled intercooler system that sits under the supercharger unit in the valley of the motor. Rated for 1,000 hp, it has thermal capacity to spare in this application.
A high-flow water pump with a 30-liter-per-minute capacity sends cooling fluid around the closed loop system to a radiator positioned low in the front of the car. The system has a water recovery tank that increases overall water volume to keep the charge temperature consistent regardless of environmental conditions.
The fuel injectors and fuel rail system are upgraded, and a set of colder spark plugs fitted to handle the higher combustion pressures. The final part of the conversion is a recalibrated ECU to accommodate the bespoke fueling, ignition and cam profile adjustments required to work with the supercharger system.
Steve Atneyel, Michael’s partner, heads Weistec’s calibration department. “Our systems are only as refined as the calibration in the ECU. We put just as much development work into engine management tuning as we do with engineering our hardware,” Steve explains.
All this sounds nice on paper, but it is the sheer quality of the Weistec conversion that most impresses when you look under the bonnet. The design and finish of the components is aircraft grade, and everything looks as though it left the factory like this.
This assembly itself is a work of art. The cog drive cradle assembly is machined from solid billet aluminum, as are the cogs themselves. Designed to work with their carbon-fiber cog belt, the system puts maximum surface contact area and minimum slippage at the top of its performance list.
The serpentine belt that drives the supercharger via the crankshaft pulley snakes it route around hard-anodized billet aluminum idlers in place of the plastic AMG stockers.
Thanks to its lightweight alloy space frame and bodywork, the SLS AMG weighs just 3,570 pounds. Its tuned, dry-sump motor gives it 571 hp at 6800 rpm and 480 lb-ft of torque at 4750 rpm for a power-to-weight ratio of 6.25 lb/hp.
The Weistec-tuned SLS 750 boasts dyno figures of 750 hp at 6800 rpm with 664 lb-ft at 3650 rpm. This translates into a power-to-weight ratio of 4.76 lb/hp, or a near 25 percent improvement.
However, it is useful to compare the power and torque curves to the standard ones to understand the difference that the extra 179 hp and 184 lb-ft make to the real-world driving experience.
The power curve of the supercharged motor mirrors the factory one at a higher level, from off idle to around 6000 rpm. After that it increases at a slightly steeper angle, which can indeed be felt from behind the wheel. In normal driving however, the much beefier torque curve is what makes the most difference to the way the car performs.
Even off idle, the supercharged engine produces way more torque than the stock motor at its peak. And while the standard engine’s curve is still building all the way to 4750 rpm, the Weistec motor has reached its sweet spot over 1000 rpm earlier.
This extra low-down torque makes a huge difference to the way the car picks up from low crankshaft speeds around town. If anything, it means you can drive around one gear higher everywhere, with the better potential fuel economy that this implies.
“When we remapped the fuel, ignition and camshaft curves, we could easily have perfectly mirrored the standard power and torque curves, and simply moved both upwards,” Steve explained.
“However, we decided to deliver a bit more excitement for our enthusiast customers, several of whom are well known professional racing drivers. So we dialed in more bottom end torque along with an extra bit of punch at the top-end,” Michael added.
On the road, the SLS 750 AMG is transformed, the supercharger’s seamless delivery boosting the feel of bottom end strength. This more muscular delivery continues through the mid-range, and at the point where the standard SLS starts to flatten and fall off, the supercharger in the Weistec-tuned version really comes on strong, delivering the sort of thrust that betters major league supercars like the Aventador.
At 6000 rpm, the standard car is 800 rpm short of its peak power, and maintains its linear power delivery all the way to the electronic rev cut-out. However, 6000 rpm is the point at which the Weistec SLS 750 picks up a second wind, delivering an extra punch that catches you by surprise the first time you experience it. This change in character adds a whole new dimension to the SLS, taking it from the realm of very fast to barking mental.
It is important to note that the output numbers for the Weistec-modified SLS are obtained with U.S. 91 R+M/2 octane fuel, which is equivalent to 95 RON octane European fuel.
And unlike many other aftermarket engine conversions, the Weistec conversion has U.S. 50-state approval, as it was specifically engineered to conform to California’s CARB emissions standard, acknowledged as the strictest in the world. The Weistec system has been awarded CARB Executive Order number D-691.
“The California test conditions are particularly insidious because they test the worst case scenarios. Some of the tests require the car to be tested cold, in Sport mode, and under heavy load up a hill, all the while following an industry standard trace, with monitoring of the hydrocarbon and nitrous oxide emissions thousands of times a second,” Steve explained.
A much more powerful car with better driveability than stock that meets U.S. 50-state emissions is the holy grail of all tuners who sell their products in the U.S. “Ironically, we have ended up with a more powerful engine that is actually a fraction cleaner than the factory standard unit in this test!” said Michael proudly.
The fact that a young company like Weistec has achieved this so early in the day with their supercharged SLS 750 AMG simply underlines the fact that knowledge, experience and a clear vision counts for more than how long your company has been around.
The Weistec CMDP system, which is the subject of a Weistec patent, neatly achieves a change in supercharger gearing, and hence boost pressure, through a change of its cog pulleys.
Who are Weistec?
At the high-end of the tuning business, when you are dealing with expensive cars and wealthy and demanding clients, pedigree and expertise are everything. Until recently, the Weistec name simply did not figure in the small circle of serious Mercedes tuners in the world, whose number you can quite easily count on the fingers of one hand.
While Weistec was only founded in late 2010, founder Michael Weiss and his partner Steve Atneyel both have an impressive track record of working with the fastest and most powerful cars. Both were engineers for major American OEM and aftermarket performance companies, Michael doing advanced engineering, while Steve specialized in computer calibration.
They decided to start up on their own and considered a direction they would both be happy with. “We were both Mercedes enthusiasts and realized that there was a gap in the market for a company dedicated to engineering state-of-the-art performance systems for cars powered by the M156 and M159 AMG motor.”
“There are a few companies that do minor upgrades with ECU and exhaust conversions, but no one provided performance engineering that these machines deserved,” Michael explains.
Weistec has grown to supply such tuners as Kleemann in Denmark and Väth in Germany with their rapidly expanding product line. Even established players in the European tuning industry have recognized Weistec as a breakthrough company, and are keen to work with them. Michael hinted that there are even more exciting things on the horizon as Weistec expands its repertoire.
2012 Weistec Mercedes SLS 750 AMG
Longitudinal front engine, rear-wheel drive
6.2-liter V8, dohc, 32-valve. Twin-screw supercharger, Weistec cylinder heads, water intercooler, pulley system, fuel injection and ECU
Double wishbone (f & r)
Four-piston, 15.4-inch ventilated and perforated rotors (f); single-piston, 14.2-inch ventilated and perforated rotors (r)
Wheels and Tires
9.5×19 (f), 11×20 (r)
265/35 (f), 295/30 (r)
While the standard engine’s curve is still building all the way to 4750 rpm, the Weistec motor has reached its sweet spot over 1000 rpm earlier.
Peak Power: 750 hp @ 6800 rpm
Peak Torque: 664 lb-ft @ 3650 rpm
0-60 mph: 3.1 sec. (est.)
Top Speed: 209 mph
Read more: European Car Web