Few racetracks in the world elicit such praise and respect as does Road America. Get it right, and you've conquered the hairy beast. Get it wrong, and it will eat you up.
Road America's high-speed straights and challenging corners are an extreme test of a car's skills and a driver's mettle, so it would seem the perfect venue for a first drive of the new SL55 AMG. It's the fastest production car yet from Mercedes-Benz, and the 493-bhp supercharged V8 is the most powerful production engine that's ever lurked behind a three-pointed star. World-class machinery on a legendary track. Could it get any better than that?
Like all AMG engines, a single technician is responsible for the assembly of the SL55's newly developed supercharged V8. The 5439cc engine's Lysholm-type belt-driven supercharger delivers a maximum of 11.6 psi (0.8 bar) of boost, the charge-temperature cooled by a crossflow air-to-water intercooler. Because it's connected directly to the crankshaft via an electro-magnetic clutch and a separate poly-V-belt, the blower reacts extremely quickly to the driver's foot, delivering boost just off idle. Refinements made to the 5.5L engine for the blower application include a faster-acting electronic throttle, revised cam timing, high-rate valve springs and lightweight valves. This is in addition to the AMG tweaks performed on the base 5.0-liter Mercedes powerplant. These include special cross-bolted connections (main bearings, etc.) in the crankcase; a crankshaft adapted to the high-torque motor using modified bearings and more durable material, with a stroke of 92mm; special heat-resistant forged pistons; new oil sump and more powerful oil pump; larger intake and exhaust runners in the cylinder heads for higher airflow rates; longer valve opening duration for improved charging of the combustion chambers; double spring assemblies in the valvetrain and lightweight retainers; and a modified ECU.
Like all AMG engines, a single technician is responsible for the assembly of the SL55's ne
No, but it could get worse. Add pavement-slicking rain showers to the mix, and what was an exciting opportunity could turn into an expensive pratfall--or worse. I'd already driven AMG-tweaked Benzes on a track in the rain, a couple of years ago at Hockenheimring, and the memory of sliding the muscular, expensive cars around a slick circuit had my imagination hurtling down a slippery slope of ugly scenarios. I also had memories of driving Road America in the rain, which did nothing to inspire my confidence, waning along with the evening light.
Still, I'd also had a lot of fun on Road America when it didn't rain, and I hadn't crashed anything that damp day at Hockenheim, so my expectations were mixed. In the Mercedes camp, the tension seemed thick as the clouds looming over the track (What does a fender cost on a $124,000 car?), but we journalists just chattered away like a bunch of monkeys. For a moment I imagined we were part of a mad experiment ("If these apes can drive the car here, in the rain, without bouncing off the walls, we've built the perfect sports car."). But then the roar of a blown V8 dopplering down the track's long front straight dissolved the fantasy, setting off a Pavlovian response to the sound of high revs and horsepower. Grabbing a helmet, I was ready for my laps.
Because of the weather, the retractable hardtop was deployed. Had I been gamboling down PCH in Malibu instead of lapping a wet track, the roof would have been stowed (it takes just 16 sec.), though at little compromise to my safety. As the SL is both a roadster and a coupe, it's been equipped with high-tech variations on accepted safety practice. An "active" rollover bar raises in just 0.3 sec. (whether the top is up or down) in cases of impending rollover, nothing new there, but now it's also activated when an acceleration sensor determines a "hazardous situation" is taking place, such as in front, rear or side impacts. A second safety consideration was side protection for the upper body and head, as the SL's folding roof doesn't allow side-curtain air-bags. Engineering solved the problem by designing a new door-panel-mounted "head-thorax" airbag that offers virtually as much upper-body protection as Mercedes' conventional setup.
Determined not to test those aspects of the systems-rich SL55, I braked early, treaded lightly on the throttle, and kept front straight speed well below the electronically limited 155 mph. And I also relied heavily on the car's arsenal of electronic traction--and braking--aids to stay almost nearly on line through the course's difficult corners.
As if the basic SL suspension weren't sophisticated enough--fully independent, with double A-arm front and five-link rear--the SL55 also offers the magic of Mercedes' active suspension system, ABC. Designed to eliminate body roll during cornering, braking and accelerating, its software in this application was rewritten for sportier handling, thus offering, states Mercedes, 68% more "stiffness" than a conventional suspension would deliver on the same car. For the track session at Road America, and for any time the driver wants the most control from ABC, a console-mounted switch allows a whopping 95% less roll than would be felt from a conventional suspension.
Interior revisions to the SL55 include an AMG sport steering wheel with Speedshift buttons--left for downshifts, right for upshifts. The automatic five-speed gearbox is virtually the same as the old SL's, though with rewritten software for the upgraded power. Other SL55-specific touches include special "Sand Cast" aluminum trim, Alcantara suede headliner, TeleAid emergency calling and 10-speaker sound system. Standard equipment includes dual batteries, nav system, auto climate control, leather-covered sports seats with integral seatbelts, power adjustment, seat ventilation and heating. Distronic cruise control and Keyless Go are options.
Interior revisions to the SL55 include an AMG sport steering wheel with Speedshift buttons
Newly engineered into the ABC system is a load adjustment mode, which adds the actual load in the vehicle to the software equation. The weight of the passenger, whatever is stowed in the trunk...probably even whether you super-sized your grease-burger combo... goes into ABC's brain, which constantly reassesses the load and alters the "rates" of each corner of the suspension.
This trick suspension contributed a stability to the car like no other I've ever felt on a racetrack. Expecting body roll, understeer and a wayward rear axle--all ills exposed in lesser cars in the harsh light of hard lapping--it took half a lap or so to realize how quickly I was going, because there hadn't been the sort of unsettling feedback you normally associate with deep throttle.
The car also went exactly where I pointed it because of the new, very precise and direct speed-sensitive rack-and-pinion steering. The system is also 13 lb lighter than the previous SL's rack. Further weight was saved by an aluminum front suspension assembly carrier. The rear subframe was kept steel because of the car's prodigious 516 lb-ft of torque through the driven wheels.
Brakes are where most cars give up first in the race environment, but the SL55 is well armed against the heat of battle. Each rotor is fully vented and perforated (as part of the build process, not drilled after the fact). The fronts are a whopping 14.2 in. in diameter and the rears are 13s. And the eight-piston calipers are sourced from development of the AMG Touring Cars.
The SL55 differs visually from the SL500: sculpted side rocker panels, chrome dual-twin exhaust outlets, diffuser rear fascia with black mesh grilles, partially tinted taillamps, badging and 18-in. wheels. The body is made of aluminum and 33% high-strength steel. Torsional rigidity is exceptional, top up or down.
The SL55 differs visually from the SL500: sculpted side rocker panels, chrome dual-twin ex
And if that weren't enough, the SL55 is fitted with Mercedes' electronic brake system in addition to the usual anti-lock and stability control systems. As well as ensuring full pedal pressure is applied during panic stops, the computer reads brake pedal actuation and then applies each wheel's brake, independently and as needed, to maintain directional stability while also slowing the car's progress. When cornering, the system increases pressure to the outside wheels and reduces it to the inside wheels, helping to prevent wheel lock, and under braking the computer varies pressures depending on speed and pedal pressure. It can even feel the sudden lift of the driver's foot off the throttle and then, anticipating an emergency braking situation, positions the brake pads onto the discs, ready for full action should the pedal be pushed. Mercedes reports this system reduces stopping distance at highway speeds by about 3%.
And if that weren't enough, when the conditions are wet, the system responds to a signal from the windshield wipers and applies the brakes just enough to keep the rotors dry.
And if that weren't enough (last time, I promise), all this wonderfulness carries a MSRP of $113,500. Fully optioned, the SL55 AMG is still well under 125 grand, which means it's a relative bargain and the 1,000 units allotted to U.S. dealers will have already been snapped up by the time you read this. Compare to the BMW Z8's $130,000, Ferrari 355's $170,000 or the Aston Martin DB7 Vantage at $152,000, and it's clear Mercedes will have absolutely no problem selling out the production run of the SL55.
If you are one of the fortunate ones to land in one of these high-tech two-seaters, consider enrolling in the AMG Challenge, a program set up by Mercedes for AMG owners wanting to explore the car's complete range of skills. It costs $850 and ensures about 2 1/2 hours of seat time in an 8-hour day at the track.
As happens with all great cars, I didn't come close to exploring the SL55's full potential. That was left to some of the pro drivers brought in to keep the journalists in check. Led by Mauricio Gugelmin, these "instructors" were soon nose to tail in a high-speed three-star convoy, serving up 150-proof shots of a very heady brew. I floated in that post-track giddiness I always feel. Great car; great track.