I vividly remember my first time in a Mercedes SLS. It was running up and down a mountain, which the California Highway Patrol had been both gracious and paid enough to shut down. All for little ol' us. From the second I lifted the gullwing door, I was smitten. Firing up the angry 6.2L V-8 put me over the top. It was fast, exotic, and an instant icon. From the sound to the straight-line performance, it was intoxicating. But then there was the handling. On that mountain road, I would turn in and the entire front of the car—roughly the length of a bowling lane—would swing out in front of you. Even though the Mercedes-Benz SLS has a high level of driver involvement, being so far away left it a bit disconnected. It's like trying to flip a light switch with the blade of a hockey stick while holding it at the very end. Note: I play neither hockey nor bowl, so my sports analogies may be exaggerated. I do, however, drive on racetracks quite often in a variety of cars, so I feel compelled to stress the legitimacy of my views on the cars.
The SLS got better with every new version and edition. By the time AMG was done, the SLS was up to something like a GT Ultimate Black Track Attack Pack, which was a fan-tastic driving car with a whacking big rear spoiler. The tendency to snap into oversteer, the secondary drivetrain movements, and the overly active rear axles had been tamed. The V-8 had become gluttonously powerful, although you still felt as though you were driving the car while sitting in the trunk.
All the lessons learned from the constant improvement of the SLS have been incorporated into AMG's second foray into scratch-built sports cars. The 2016 Mercedes-Benz AMG GT-S is the culmination of the tireless improvement that went into the SLS, coupled with the latest in technology. The mighty 6.2L naturally aspirated V-8 is no more. It was thirsty on the intake side and dirty, by modern standards, at the tailpipes. In its place is a far more efficient and power dense 4.0L twin-turbo V-8 producing 503 hp and 479 lb-ft of torque. All 479 of those lb-ft are available from the low-low revolutions of only 1,750 per minute. To really get into the nerdery of the V-8, see the sidebar accompanying this feature.
A seven-speed dual clutch transaxle is mounted in the rear of the car, allowing for the slightly rear biased weight distribution. A claimed 53 percent of the mass sits on the rear axle, which AMG engineers claim is ideal for performance cars. Power is transferred from the engine in front via a filament-wound carbon-fiber driveshaft. The unit is stiffer and lighter than steel, cutting down on vibration. Inside the rear transaxle is an electronically controlled locking differential. By controlling the degree of lockup, AMG can change the behavior of the car to suit conditions, and the differential can be tightened up to stabilize the car under braking and also during acceleration to maximize grip. It can also be loosened up during turn-in or lighter power applications to free up the car to rotate easier without wheel slip.
Drivetrain movement was one of the issues on the SLS. Under lateral loads, the drivetrain would move side to side. You turn in, the car takes a set, and then the drivetrain slides over and gives the car a little nudge from the inside. Since the drivetrain mounts below its center of gravity, it would do the same thing in roll as well.
The GT-S uses a passive unit, but the AMG Dynamic Plus Package features active, magnetorheological mounts to fix that movement problem without adding NVH, that's noise, vibration, and harshness. AMG engineers didn't eliminate the movement wholesale, however. The issue that challenged them in the past is now working for them, and the degree and timing of mount stiffening is tuned to match the desired dynamic characteristic.
Although active damping is available on the GT-S, the most notable changes are far more basic. AMG started by changing the basic kinematics of the new car compared to the SLS. All the suspension components are forged aluminum. The front suspension was redesigned to incorporate more negative camber to increase grip while cornering. In the rear, the lower shock mount was located farther outboard, as close to the hub carrier as possible. Ideally, engineers look for a 1:1 motion ratio between wheel and damper. This allows for maximum attenuation of unwanted movement and vibration. To control unwanted geometry changes, the suspension bushings are molded out of rubber with roughly the same durometer as wood.
To get the full effect of all the changes, AMG invited us to drive the cars from downtown San Francisco to Monterey using the most scenic route possible. We ended the event lapping Mazda Raceway Laguna Seca, which my wife now refers to as my second home. A few more trips and she says it may be my first.
The SLS is a great car on the road, simply because of the sense of the occasion. For all its minor faults, it is still one of the greats. The SLS is now one of the greats, but we don't have all the faults to overlook. I will, however, start with my biggest complaint. No gullwing doors. I don't miss banging my head on them getting out of the car, but there is nothing that makes you feel more like Chuck Yeager than coming to a stop and swinging open that door. For bonus points, swing the cockpit hatch up while you're still rolling. But I digress. You can get in and out of the GT-S without any great feats of gymnastics.
The interior of the GT-S is a more hospitable place to spend long periods of time. While the GT-S is a smaller car, it feels far more open than the SLS. It turns out, those wing door hinges also take up a decent amount of headroom. The seats are supportive and mounted low to the floor. The seating position requires stretched-out legs, but the requisite flat-bottom steering wheel has enough range of motion that doesn't also require stretched-out arms. The dash and center console wrap around both occupants. The small electronic shifter feels like a spacecraft throttle and sits right behind the latest version of the Command System controller. The experience is as luxurious as you'd expect of anything with the three-pointed star, yet still sporty. You won't confuse the GT-S with an S-Classe Coupe, but I wouldn't want to.
On the tight streets of San Francisco, the GT-S wasn't at all intimidating to drive. The SLS sometimes left you wondering exactly how far out those corners hung. The GT-S is tighter and more manageable. The transmission around town is certainly a bit more aggressive than the traditional automatic found in other AMG products, but certainly smoother than most exotics. In comfort mode, gears click off with a little nudge and the burble from the tailpipes changes note. While cruising, the exhaust noise fades away and the car is nearly e-Class quiet.
Turn the dial to Sport and the exhaust wakes up, the throttle tip-in becomes more aggressive, and the transmission is more precious with gear changes. Traveling near the coast, the road transitions from a perpendicular grid to landscape following meandering. The GT-S eats this up and feels right at home ticking off miles. I decide this would make a perfect weekend getaway car the next weekend my parents are in town to watch their grandchild. More miles roll by and I start imagining a cross-country trip.
The Pacific Ocean gives way to mountain forests and meandering turns evolve to more urgent switchbacks. In the tightest of areas, the GT-S starts to show its size. Driving faster requires far more precision. Luckily, this car has loads of it. Unlike its predecessor, you know exactly where the car is and where it will end up; there's no sloppiness here. It comes off of corners well without smacking you with all the torque at once, unlike previous forced-induction AMG products. It delivers power in a similar way to the old naturally aspirated V-8. Most importantly, the car is fun. The early SLS had a quality that went beyond respecting the car and crossed over to fear.
This became more apparent on the racetrack. I was able to work up to speed quicker than I predicted. It really is a driver's car. The stiffness of the space frame, coupled with all the advances in the suspension have made for a very planted car. The electronic rear diff is working wonders as well. If you find yourself a little out of sorts around the apex, easing into the throttle immediately settles down the car. The weight rolls back, the nose snaps in line, roll in, and go.
The GT-S has both Sport+ and Race Mode; Sport+ being extremely forgiving and offering a helping hand without criticizing. Race Mode allows you more control of your own destiny. You can prod the back end loose and get the car to rotate around on braking as well. Traction control is still there, but once it's stepped in, you will have lost a decent amount of speed.
The car is fast, full stop. Off of corners, on the front straight, up the hill, it pulls and pulls. It sounds good as well. Nearly as good as the 6.2L. Even after seeing a cutaway of the mufflers, I still don't understand the voodoo magic involved with getting a smallish turbocharged V-8 to sound like a muscle car. The transmission is just as good. If the car was in Race Mode, I spent half of my time in automatic, not seeing a need to use the paddles.
After a day of journalists lapping the cars at the track, the Michelins were definitely showing wear, but nothing abnormal. The shoulders of the tires weren't burnt off, more than likely a benefit of the added negative camber, and the tread wasn't coming off in chunks. Also a sign of good utilization of the whole tread width. The brakes never showed signs of fade, and the engine never showed signs of heat soak. The 911 has some real competition in the daily driveable track day special.
While I certainly miss the gullwings, I have fallen in love with the GT-S. The doors aside, I think this is a better-looking car from every angle compared to the SLS. It's almost what the SLS should have been. Mercedes says the first customer cars will begin arriving this spring. Pricing is $130,825, which puts it right in the center of a very competitive market. Luckily, the GT-S has the chops to compete.
The M178 in Detail
As much as I love the 6.2L monster V-8 powering the AMG SLS and the C63, I knew its days were numbered as soon as the engineers from Affalterbach gained a renewed interest in turbochargers. In terms of efficiency and power density, you can't beat a force-fed engine gaining extra power from energy normally thrown away as heat out of tail-pipes.
Let's talk specifics. Maximum boost will be 17.4 psi, while the compression ratio sits at 10.5:1 thanks to direct injection. Bore measures 83.0 mm, while in comparison stroke is a relatively long 92.0 mm, which is good for that mountain of low-end torque. Those numbers might sound familiar, as this new V-8 is basically a pair of 2.0L I-4s that power the CLA45 sitting at 90 degrees from each other. The turbos sit in the V's valley, making this a "hot-V" layout.
Also like the CLA45's engine, using air-to-water intercoolers hanging off of the front of the engine minimizes the path of the charge air, and the diameter of the charge pipes is kept consistently large from the compressor's outlet to the throttle body. The turbo's turbine sides exit into a large pipe similar to a two-strokes expansion chamber.
AMG says the assembled engine weighs in at 460 pounds, dry. The engine block uses a closed deck design and is sand-cast in aluminum. The cylinders are lined with Mercedes' NANOSLIDE technology, which has been in service in more than 200,000 engines since 2006. Once the cylinder liners are in place, the bores are conditioned using a process called "spectacle-honing," which involves bolting a fixture to the block and torquing it in place to replicate whatever distortion may be caused by the installation of the head. All of this work combined with a specially designed low-friction piston ring package works to reduce fuel consumption, power loss through parasitic friction, and oil consumption.
At the bottom end of the engine, AMG has employed dry-sump lubrication to not only fight starvation under high-g loads, but the smaller sump also allows the engine to be mounted 2.2 inches lower in the car. At the opposite end, the four-valve heads are constructed of zirconium alloy to resist thermal loads and minimize heat soak inside the head. Variable camshaft timing is utilized on both intake and exhaust cams.
The M178 in the GT-S produce 503 hp at 6,250 rpm and 479 lb-ft of torque starting at 1,750 rpm and continuing up to 4,750 rpm. You can see the tabletop flat-torque curve in the accompanying graph.