IndyCar driver Graham Rahal called and asked if I’d like to drive his modified CLK63 AMG Black Series. Well actually, the guys at Weistec Engineering called to see if we’d like to drive a CLK Black Series belonging to Graham Rahal that they’d just supercharged. Close enough.
I don’t remember anyone ever complaining about the 500-hp Black Series being slow, but it does have to haul around 4,000 pounds. And being an over-square engine means peak power comes at the upper rev range. In the Black Series that’s 6800 rpm, and its torque (465 lb-ft) peaks at 5250, so you definitely have to be committed if you want the full effect. And while Rahal himself loved the car in stock form, he admitted he “always wanted a little more power.”
The guys at Weistec think it’s possible to have both a high-revving, top-end oriented engine and plenty of usable power down low. Of course they would, as they’ve designed a supercharger that works with every M156 6.2-liter V8 that’s stuffed in a wide range of AMGs—S63, SL63, ML63, E63, C63 and SLS, and the CLK Black Series. With four-valve heads, instead of the three-valve heads on the M113 E55 engine, Weistec’s tests showed it to have outstanding flow characteristics throughout the rev range and that meant there was a fairly large window for more power. Weistec felt the engine was just begging to be supercharged.
After testing a variety of supercharger systems, including a look at what Mercedes did with the E55, Weistec went with a twin-screw, instead of roots-type, system because of the twin-screw’s efficiency. The screws are housed inside a precision-cast, T-6-hardened, 356 aluminum alloy of their design. What makes the system different is what Weistec calls its “Constant Mu, Delta Pressure” (CMDP) cog drive system designed to maintain constant friction (Mu) between the belts and pulleys. This reduces belt slippage and maintains consistent boost (Delta) pressure. Conventional supercharger systems use a smaller pulley to raise boost pressure, but the smaller pulley has less surface area and can increase the chances of belt slippage and inconsistent boost levels. With Weistec’s system, boost pressure is altered by changing the cog pulleys within the CMDP drive system instead of changing the serpentine belt-driven pulleys on a conventional supercharger system. Unlike any other, Weistec’s CMDP is currently patent-pending.
According to the company, the twin-screw compressor also allowed for a wider range of power levels compared to a roots-type system. It is offered in three stages, with an added “plus” designation for cars with aftermarket exhaust systems. The kit in the CLK Black Series here is a Stage 1+ working with Evosport long-tube headers and 3-inch X-pipe exhaust. Using 7.5 psi of boost, it delivers a staggering 549 whp at 6000 rpm and 543 lb-ft of torque to the wheels at 4400 rpm. That’s up from 421 and 402, respectively, without the supercharger but utilizing the Evosport headers and exhaust. Final testing is still being done on Stages 2 and 3 so official figures haven’t been released, but Weistec did let on that one customer running a Stage 3 setup is making as much as 700 whp. Weistec’s also confident that the Stage 1 kit will be CARB certified by the time this story goes to print.
My first impression is how well Weistec managed to retain drivability even though the engine’s sending 470 lb-ft of torque to the wheels at 2000 rpm. Other supercharger systems often have touchy throttles that cause the car to lunge a bit more than desired, making it difficult to drive smoothly in slow traffic. Weistec’s setup allows for a good deal of throttle modulation before the full benefits of the supercharger come into play. And the boost feels like it’s fed in progressively, instead of the all-or-nothing of some systems.
Get pushy with the loud pedal and the engine starts to wake up. There’s enough power down low to blister the asphalt and send the traction control into working overtime. The power builds exponentially, without dropping off as the tach needle flicks towards redline. Behind you, the unfiltered exhaust system lets out a feral howl with every run up the gears.
Ferocious power like this can oftentimes overwhelm a chassis but, in this case, AMG’s chassis engineers have made sure that almost any amount of extra thrust is kept in check. You can sense there are terabytes of setup data that AMG has gathered from its racing programs and applied it to the CLK63 Black Series. The result is the best-handling Merc I’ve ever had the pleasure to toss around.
For starters, it doesn’t feel like you’re carving canyons in a 4,000-pound car. It feels lighter than an M3 and more like 3,400. The steering is intuitively direct and informative, and thanks to a different front apron with relocated mounting points that give the front suspension more negative camber, the turn-in is sharp. While most Mercs feel nose heavy and enter corners with tire-scrubbing understeer, the CLK Black and its Pirelli P Zero Corsas cut a surgically precise line to the apex without fuss. From there it’s just a matter of measuring the amount of straightaway and how much devastation you’d like to wreak with the accelerator. Feed in too much throttle too soon in the corner and the rear tires will be overwhelmed, producing delicious power-on oversteer that’s easily controlled with the throttle.
Suspended with adjustable KW coilovers, the car rides firmly but acceptably for an enthusiast. According to Weistec, the suspension settings for height, rebound and compression remain as they came from AMG. The car stays unbelievably flat through corners and hardly dives or squats under hard braking and acceleration. That makes stringing along a series of turns, be they tight hairpins or fast sweepers, an exercise in fluidity, grace and easy speed.
The only other major changes Rahal made to the car are a set of 19-inch Volk G2 wheels encircled with the stock Pirellis. The Volk wheels are a pound or two lighter than the standard Alcoa-made forged wheels, improving unsprung weight.
Extra power and a slight decrease in unsprung weight are probably the only changes the Black Series needed. Although I hadn’t driven one before, it’s easy to assume that there was more chassis than engine, especially considering how well the stock setup copes with the extra power. Looks like Weistec found the right niche in the AMG 6.2-liter engine, and the cars that use it. The customers aren’t complaining. “It was a fun car before, but nothing like it is now. The only problem is I can’t keep my foot out of it!” Rahal says.
You can sense there are terabytes of data that AMG has gathered from its racing programs and applied that to the CLK63 Black Series.
Weistec CLK63 AMG Black Series
6.2-liter V8, dohc, 32-valve. Weistec twin-screw supercharger system, Evosport long-tube headers and 3-inch X-pipe exhaust, BMC air filters
Six-piston calipers with 14.2-inch vented rotors (f), four-piston calipers with 13-inch vented rotors (r)
Wheels and Tires
Volk G2, 9x19 (f), 10.5x19 (r)
Pirelli P Zero Corsa 265/30 (f), 285/30 (r)
Peak Power: 549 hp @ 6000 rpm
Peak Torque: 543 lb-ft @ 4400 rpm