Between 1967 and 2005, AMG achieved incredible success by following a simple corporate ethos: If your pockets are deep enough, we will build it for you. The “shoehorning” of enormously powerful, naturally aspirated engines into undersized Mercedes-Benz chassis quickly became AMG’s particular claim to fame, and displacement has long proved the company’s preferred commodity.

For those customers with the financial capability and desire to have something truly special, from April 1999 to May 2001, AMG quietly offered the autobahn-storming monster presented here: the SL 73. Produced in an extremely limited (and never officially marketed) run of just 42 reported customer units priced in excess of 350,000 DM (~$168,000) each, the SL 73 is a snarling, snorting, actualization of “an iron fist in a velvet glove.”

Don’t be fooled by its refined bodywork, supple upholstery, or 4,500-pound curb weight; it is a brutal machine capable of eating pavement (and its own rear tires) with disconcerting speed and panache.

At the heart of the SL 73 is the wondrous 6.0-liter V-12 engine from the contemporary SL 600, which AMG has bored out to 7.3 liters and stuffed with upgraded internals and engine management software to unlock 520 horsepower and 550 pound-feet of torque. Thankfully, AMG technicians also comprehensively fettled the car’s brakes and active damping systems to cope with the extra power, and the result is a traction-restricted 0–60 time of 4.6 seconds and a top speed approaching 200 mph. In keeping with its understated, gentlemanly appearance, the only accoutrements which externally hint at this super-exclusive model’s athletic potency are its twin chrome-finished exhaust tips and its five-spoke AMG wheels.

Parallel to the SL 73’s production run, AMG also sold a quantity of these 7.3-liter V-12 engines to the Italian supercar manufacturer Pagani Automobili. By late 2001, Pagani had begun fitting them into their Zonda model, and this notable arrangement continued for every naturally aspirated Pagani built up until 2017. If AMG’s unconfirmed production numbers are to be believed, then it seems worth noting that tracking down an SL 73 is several times more difficult than finding a 7.3-liter powered Zonda.

Like many of the ultimate AMGs of this era, this well-preserved SL 73 AMG was delivered new to a Japanese collector in October 1999. Japanese export documents (on file) show regular mileage entries until January 2015, when this SL 73 was exported to Switzerland then showing approximately 31,400 kilometers (~19,510 miles). The car’s last recorded Japanese registration was in the Adachi City, with plate “399 9051.”

Offered today with fewer than 35,000 kilometers (~21,750 miles) on its odometer at time of cataloguing, this SL 73 benefits further from a suitably intimidating “triple black” color scheme of black paintwork with color-matched body cladding and a black soft top (plus hardtop) over black leather interior upholstery. A complementary suite of bright maple burl trim brings a welcome contrast to the miles of rich black leather upholstery, while the 300-km/h speedometer offers the sole hint to any occupants that something unique lies beneath the hood.

The SL 73 AMG’s understated aura wholly belies its overwhelming performance. This generation of Mercedes-Benz’s famed SL-series is already appreciated as a modern classic, and this stunning example of the rarely seen SL 73 cannot be considered as anything other than the absolute pinnacle of the range.