Back in the late '70s, Steve Dinan was running a repair shop and saw that his customers were being underserved by the aftermarket, which was in turn making his job more difficult. "The quality of most of the stuff was so bad that you couldn't put it on the car without having some kind of malfunction," he says. "In the beginning, I wasn't planning on going into parts manufacturing—my goal was simply to modify cars. But every time we ran into a problem with a part, I ended up re-engineering it to fix whatever was wrong with it."
That eventually led Steve to start Dinan Cars, a BMW tuning house that became so respected over the years that Dinan-modified vehicles were allowed to retain their factory warranty coverage and even qualify for BMW's Certified Pre-Owned program. Dinan's holistic approach to road car tuning wasn't primarily focused on producing eye-popping numbers for a spec sheet; it was about improving on a car's strengths while addressing potential weaknesses. "I think a modified car should drive like a factory car—just faster," he explains.
In 2013 Dinan Cars became part of the Driven Performance group, and after a two-year transition period, Steve parted ways with the company he built and joined up with Chip Ganassi Racing to assist with Ford's factory racing efforts. But with the reborn GT now bowing out of racing after class wins at Le Mans and elsewhere, Steve's been hard at work with his latest endeavor, CarBahn Autoworks.
The overall philosophy hasn't changed much since the Dinan days, but there is one notable difference: Steve's now applying his special brand of tuning magic to not only BMWs, but to Porsches, Audis, and Mercedes-AMG models as well.
This GTS-spec C63S is the first example of the latter, a mid-level tune with tweaks that bring more power, grip, and chassis refinement to the table. But Steve assures us it's not just about turning up the boost and adding a stickier tire. To get a better sense of how it all works together to take the C63 to the next level, we sat down with Steve for a chat about his approach to modification and then headed for the outskirts of Los Angeles to put CarBahn's latest machine to the test.
Astute readers will note that, in much like Dinan's relationship with BMW, AMG got its start as an aftermarket tuner for Mercedes-Benz vehicles before becoming the performance arm of the brand. But as is often the case, with mainstream adoption comes the compromises required to keep mainstream customers happy. "Each manufacturer does something a little better, and usually something a little worse, than the others," Steve says. "I felt like the Mercedes had great styling, a good interior and user interface, and I thought the powertrain was very good. But I thought the chassis of the car was lacking. The car has a lot of stiffness, particularly at the rear. That helps prevent understeer, but the car just couldn't really put the power down off the line or out of a corner."
So while CarBahn has added bigger turbochargers, larger heat exchangers, a cold-air intake, and modified the ECU make use of the additional boost as part of the GTS package, which brings the C63S's power up to a lofty 674 horsepower and 666 pound-feet of torque at the flywheel, it's the chassis tweaks that Steve's perhaps most proud of. "Adding power is easy—that took six months of development," he tells us. "Then we spent another year and a half fixing the suspension."
As you'd expect, the springs were a key component of the transformation, custom-made progressive rate coils that work in conjunction with the factory adaptive dampers. "We wanted to soften the rear suspension, but not the car overall," he says. "So we added five percent to the front spring rate and the front sway bar, and subtracted five percent from the rear spring. And then we got rid of the understeer by putting a significantly wider tire on the front—the car came with a 255mm from the factory, we moved up to a 285. And because the front end's stiffer, the load transfers to the rear better, which now puts down power far more effectively than it did in stock form."
CarBahn didn't stop there, though. They tossed the factory rubber bushings and replaced them with eccentric bearings to get rid of the play caused by the rubber's tendency to deflect under load. "Everybody thinks that when you put bearings in the suspension, the car will ride worse," he says. "Believe it or not, it actually rides better. It does create more noise, but we felt like the gains in traction and ride quality were much bigger than the compromise in NVH was."
Our tester was also fitted with CarBahn's Street Aero package, which adds a functional front splitter and ducktail-style rear spoiler that together generate 100 pounds of downforce at 150 mph to enhance high-speed stability. It's also equipped with what the company says are the largest and lightest wheel and tire package available for the C63, a set of 20-inch Forgelines measuring 9.5 inches wide up front and 10.5 inches at the rear, wrapped in Michelin Pilot Sport Cup 2 rubber.
In a world full of over-the-top wings and scoops, CarBahn's use of restraint with the C63S is refreshing. While the trained eye will immediately note the hunkered down stance, big wheels and upgraded aero, there's nothing here that feels inelegant or wholly out of place. Instead, CarBahn has opted to add a subtle dose of aggression that makes the car more sinister without venturing into the realm of garishness. Form follows function, just as it should.
Accordingly, the interior is left untouched from its factory form. The car's well-spec'd in that regard though, outfitted with AMG sports seats with adjustable side and thigh bolsters, a Burmester audio system, and a few other choice options. And since the factory active exhaust system's still intact, it isn't until we actually put the car into gear that CarBahn's mechanical handiwork became truly evident, with the big turbos whooshing and hissing as we transitioned on and off throttle.
Despite the lowered ride height, the car is indeed surprisingly compliant in Comfort mode, soaking up potholes and other inconsistencies in the road with very little drama. There is a bit more chatter coming from the road, due in part to the suspension tweaks, but also because of the big hoops and Cup 2 rubber we're rolling on. Opening up the exhaust a bit by way of the hard button on the center console makes it ostensibly a non-issue.
While 674 horsepower is quite a bit of grunt, let's not forget that a stock C63S isn't exactly a slouch, either. A new sense of urgency is clearly evident though, and it feels less apt to run out of steam as the speeds climb out in the Angeles Forest, but the 4.0-liter twin turbocharged V8 does forfeit some of the factory setup's linearity as a result.
Clicking the drive mode selector into Sport tightens up the car's body motions substantially with only a minor penalty in ride quality. We later discovered that it's Steve's preferred suspension setting, part of the custom preset he's programmed into the car's Individual drive mode. It turned out to be surprisingly similar to how we'd dialed everything in through the hard buttons on the console—loud exhaust, sport dampers, manual transmission control via paddle shifters, and Sport-level traction and stability control intervention. Sports car response for the real world, basically.
Paired up with the tenacious grip of the Cup 2s, the C63S felt noticeably more eager to turn in and change direction, cornering with more precision in general, which in turn translates to more confidence at the helm. The car felt planted rather than over-sprung—a common pitfall in the tuning world—and legitimately better to drive on the whole.
The GTS package comes out to $21,890 and includes the aforementioned powertrain and chassis upgrades, while the wheel and tire package will set you back an additional $9200. All components come with a four-year, 50,000-mile factory-matching warranty.
CarBahn will also sell its upgrades a la carte for those who prefer to pick and choose their upgrades. But going that route does work against the company's design philosophy to some degree, Steve tells us. "For us, it's a holistic approach—we look at the entire vehicle," he says. "When we make an improvement in one area, we look at how that affects the balance overall and make changes where needed. We sell parts individually, and that's the way most people buy them. But when they buy whole conversions, they end up with a vehicle like this one, which I think is a pretty extraordinary car."