The last time I checked, the needle had just nudged past 174 mph, its progress slowed slightly as the car fought its way through a wall of air that was becoming ever more resistant. Even so, the Vaeth-tuned 6.2-liter in the C63 wasn’t letting up. It stayed angry, insistent and more than willing to prove that its v-max was 200 mph. As the speed climbed, the extra downforce from the front and rear spoilers made it feel as though the screws were being tightened and the car was being pressed further into the tarmac. Traffic is sparse on this stretch of no-limit autobahn just outside of Hosbach, Germany, and the wide-open left lane was every speed freak’s wet dream.

When you pass a car that’s going 100 mph slower in the lane next to you, it doesn’t look like it’s standing still. It looks like it’s in Reverse and the driver has the pedal nailed to the floor. They flash by with a quick whoosh just a few feet away. It’s unsettling if you think about what would happen if they dropped into your lane with 100 mph between the two of you, but most of your attention is focused on the road in front of you, or what you can see of it, because, for the most part, much of the road is a blur.

Sitting in the front passenger seat that afternoon was Wolfgang Vaeth (Väth in German), the founder of the tuning firm that bears his name. Before I sat down behind the wheel, he told me he was “a bad passenger,” which I interpreted as, “I hope you don’t suck at driving, because you might give me a heart attack.” Normally a charismatic, old-school tuner with strong opinions and impeccable comedic timing, Wolfgang Vaeth sat in nervous silence as I guided the C63-based, low-flying missile his company created.

When Wolfgang Vaeth gives you a tour through the Vaeth facilities, it’s akin to a history lesson. The shop is still based out of an old flour mill in Hosbach that he opened back in 1977. As you walk through the various departments, Vaeth will point out the old, reliable and seemingly indestructible machines he still uses to balance crankshafts, bore cylinder blocks and port heads. The company is as much a restorer as it is a tuner. On my visit, Vaeth pointed out a crankshaft from a 300SL Gullwing. A few feet away sat a race-spec cylinder head for their 190 2.3-16 track car. Suffice it to say, there isn’t anything with a three-pointed star that Vaeth can’t either restore or tune.

We came up a bit short of the car’s claimed 200-mph v-max on that run because of traffic, but it didn’t matter. What mattered is how it felt on its way to the serious side of the speedometer. The car’s composure was stoic, its demeanor was all business. When you enter into the surreal realm above 150 mph, a car’s weaknesses will be exposed and magnified: too much lift, weak brakes, sloppy steering, too softly sprung or damped, a lack of top-end grunt, or, in other words, confidence killers. The Vaeth-tuned C63 displayed none of those characteristics on that high-speed run. It felt as though it could run that speed all day.

Vaeth’s top-of-the-line tuning program for the C63 is known as the V63RS. It’s a 572-hp and 502 lb-ft rework of the C63’s 6.2-liter, AMG-tuned V8. The core modifications include an ECU reprogram, a high-flow air filter, a stainless-steel exhaust system and high-flow catalytic converters. But the car I drove that day belonged to the kind of client tuners salivate over.

Not content with ordering from the menu, this car’s owner wanted something special, something stealth, something designed for a single purpose. Already an owner of a Vaeth-tuned CL65 and a SL65, both capable of 200-mph-plus, the C63 would be his “beater,” if you will, good for late-night ’bahn storming, and it could be parked on the street without much concern about door or bumper dings. It had the telltale patina of hard use: a paint-chipped and bug-stained front bumper, tarnished emblems, nicked wheel rims and a lot of kilometers on the clock.

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