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Sometimes it’s hard to tell which is the cart and which is the horse. Sometimes, in automobiles, it doesn’t matter which goes first. There is engineering (product) and there is marketing (hype), and now there is a new showpiece V8 from AMG. It’s called the 6.3.
The 6.3 stirs emotion on at least two levels. For the foreseeable future, this engine will power most of the hot rod Mercedes crafted by the firm’s high-performance subsidiary. It generates wads of horsepower and torque—nearly 500 units of both—and it’s more refined at the extreme edge of its performance envelope than the tweaked Mercedes V8s it replaces. Figuratively, the new 6.3 connects AMG with its glorious past and the mother company’s past. Its name is symbolic, even if the symbolism follows a slightly convoluted path back to the 1960s.
The designation 6.3 is rich with heritage at Mercedes-Benz. To aficionados, it represents a car more than an engine—one of the finest cars in Mercedes’ post-World War II stable. The original 6.3-liter V8 debuted in 1962 in the new M-B 600 uber-sedan, which was to the mid-’60s as the Maybach 57 is to 2006. Known internally as the M-100, the first 6.3 V8 was a he-man among boys, with engineering decades ahead of the curve. It featured fuel injection, aluminum cylinder heads, overhead camshafts and sodium-filled valves, with forged pistons, rods and crank. Each hand-built copy was bench-tested for 265 hours, 40 of which were consecutive at full load.
In 1966 a roguish Mercedes engineer named Erich Waxen-berger hatched a plan, and he intended to implement it whether the tri-star went along or not. As a private venture, Waxenberger installed an M-100 in Mercedes’ 300 SEL—the company’s standard full-size six-cylinder sedan (codename W-109, or six generations of S-Class past). Darned if the powers in Stuttgart didn’t like what Waxenberger had wrought. In 1968 Mercedes introduced the 300 SEL 6.3. The 6.3, as it was known, continued in production through 1972 and laid the groundwork for the subsequent M-100-powered 450 SEL 6.9.
The 6.3 was Europe’s muscle car, arguably the first super sedan and progenitor of all the AMG, M and RS cars that followed. Its performance shamed dedicated sports cars like the Porsche 911, and its air suspension allowed impressive handling and stability. The M-100 V8 generated 300 hp and 436 lb-ft of torque; matched with a four-speed automatic, it propelled the 6.3 to 60 mph in 6.2 seconds. The 6.3 could cruise all day at 140 mph, with four of its five occupants licking ice cream cones as they enjoyed music from the Becker stereo.
Coincidentally, AMG was formed the same year Mercedes launched the 300 SEL 6.3. In the early days this prototypical tuning firm was just that—a tuner kept at arm’s length by the mother company, known only to a relative handful of performance nuts. Yet by 1971 AMG had planted itself indelibly in the automotive landscape. That year it prepared a 300 SEL 6.3 that went from nowhere to a class victory at the 24 Hours of Spa, finishing second overall. To be sure, AMG’s race car wasn’t really a 6.3. Its M-100 was punched out to 6.8 liters.
Fast forward 35 years. AMG has been a wholly owned subsidiary of DaimlerChrysler since 1999, and a new 6.3 V8 is its first engine designed and developed entirely in-house. Its block (bore centers) is different from that used for the new four-valve, 5.5-liter Mercedes V8 introduced in the 2006 S-Class. AMG’s 6.3 was created for “higher specific output and specific torque than any other series-produced naturally aspirated eight-cylinder engine in the world,” according to the company, with “20 percent more torque than comparable naturally aspirated engines with a similar power rating.”
Whether or not AMG’s claims are accurate, the new V8’s nomenclature technically is not. It is barely a 6.2, displacing 6208 cc. The “6.3” nonetheless features high-tech parts and materials you would expect from Mercedes’ captive tuner, and some things you might not expect. The intake and exhaust ports are vertical, to maximize airflow velocity, and the valvetrain is stiffened with features like bucket tappets to support smooth operation at the 7200-rpm redline. The main bearing caps are not caps at all, but a fully boxed lower crankcase section that virtually eliminates crank flex. There are no bore liners in the aluminum block. The cylinders are coated with a micro-thin, electrostatically applied ceramic/metallic material and then machined.
AMG’s V8 has dry-sump lubrication, like the original 6.3, but it also applies technology that engineers developing the M-100 probably could not have imagined, including four-cam phasing and a variable intake system with two integral throttle flaps.
The most important stuff? Horsepower will vary as much as 40 in various 6.3s, depending on vehicle configuration—and the amount of air AMG can move through its new V8. Yet in all cases, it’s impressive: 475 hp at 6800 rpm in the forthcoming CLK63, 503 hp in the ML63 and RL63, and 514 hp in the CLS63. In each, the 6.3 V8 generates more horsepower than AMG-tweaked variants of the three-valve Mercedes V8 that previously powered these cars, supercharged or not. That said, the 6.3 generates less torque than the previous supercharged 5.5: 465 lb-ft compared to 516 lb-ft.
AMG cars built with the 6.3 will be the first to use Mercedes’ seven-speed automatic transmission, labeled the AMG Speedshift 7G-Tronic. Massaged to handle mega torque and improve response, this ransmission reduces shift time 50 percent in manual mode, compared to the standard Mercedes version, according to AMG. The AMG 6.3s will also come standard with new composite brake rotors and a feature called Racetimer. Similar to Porsche’s Sports Chrono option, Racetimer records acceleration, top speed or lap times and stores them for retrieval at the driver’s request.
In the CLK63 AMG, the new V8 is a welcome improvement. Previously powered by the naturally aspirated 5.5, this car was merely fast. With the 6.3 and seven-speed, it’s blindingly quick. Throttle response is instantaneous, automatic downshifts nearly so, and the manual-control electronics are better programmed to hold a gear near the redline. This is one of the most impressive powertrain combinations from Mercedes in years—smoother at high revs than the previous AMG engines. There’s a nice burble at part throttle, and something more like a banshee scream when you floor it.
The CLK was already one of the most driveable cars in AMG’s inventory; with the 6.3 it’s more so. No Active Body Control here—just good suspension tuning, decent steering feel and crisp turn-in. Some Mercedes-Benzes will dutifully go along for the ride when pushed, behaving quite predictably all the while. The CLK63 relishes a kick in its flanks. Of course, we sampled the 6.3 in a CLK coupe, and coupe people on this side of the Atlantic won’t get the same opportunity. Mercedes will send only the CLK63 cabriolet to North America.
We also tried the forthcoming ML63 AMG, and the package certainly has its appeal: a people hauler to engage 911s in the stoplight derby or blast through big sweepers much faster than decorum or good sense might suggest. Yet through the twisties where we sampled it, changing directions quickly and often, the ML63 is not exactly fun. Its massive tires mean plenty of grip. The steering is fairly quick for such a hefty machine, but also quite light, and the package conspires to feel twitchy—almost unsettling.
The AMG 6.3s will reach the United States as 2007 models. The CLK cabrio arrives in July (expect a substantial price increase over the existing model’s $83,275) and the ML in August, with the CLS and R-Class (there’s an interesting concept) some time after that. Buyers will no doubt be waiting.
Mercedes sold nearly 20,000 AMG cars in calendar year 2005—more than the entire run of M-100-powered cars over that engine’s 19-year production span. One technician assembles each AMG engine, start to finish, so the crew in Affalterbach is clearly busy.
The 6.3 is the new cornerstone of AMG’s identity. Director Wolf Zimmerman says AMG needs an engine all its own, despite what those 20,000 sales might suggest. In 10 or 15 years we’ll begin to know whether history judges the new 6.3 as reverently as the M-100 V8.
In 2006 the 6.3 is impressive, if not incredible. The 7.0-liter LS7 Corvette V8 generates similar power (505 hp, 470 lb-ft, 7100-rpm redline), with one fixed-timing cam and pushrods. Zimmerman says there is probably 50 more horsepower in the AMG 6.3, if AMG can figure out how to eliminate intake or exhaust flow restrictions in the various vehicles. If the market demands substantially more, it’s back to a blower of some sort.
Mercedes has a remarkable history of supercharging, by the way, dating all the way back to the early 1900s.
