Mercedes-Benz’s V-12 engine isn’t dead yet despite regulatory predation and increasingly power-dense V-8 engines painting a bleak future. As the lights dim on the big 12, it is now built only by AMG’s technicians and is only available stateside in a single non-AMG model, the Mercedes-Maybach S650. Back in the 1990s, though, Benz’s V-12 was the new thing in town, and graced the priciest, most dignified versions of the S-Class sedan and coupe, as well as the SL convertible.
The 6.0-liter V-12—the same size as the current unit but lacking today’s pair of turbochargers and 2o-plus years of technological advancement—announced itself with a long, airplane-style starter whirring noise, a sophisticated exhaust thrum, and a set of bumper-sticker-sized “V-12” badges on models so equipped. It dripped with needless excess, but for some, it apparently wasn’t enough. Which is why Mercedes, during its expansion phase with the V-12, handed an R129-generation SL600 with the engine over to the performance-addled minds at AMG and let ’em rip. Thus was born the SL70 conversion by AMG.
AMG’s twisted math goes like this: Take one 6.0-liter V-12 from a car named SL600, bore it out for another liter of displacement to achieve 7.0 liters total, then rename it SL70. Never mind that “70” is a smaller number than “600”—the seven part is bigger than the six part, etc. And besides, German automakers long ago abandoned the practice of logically tracing engine displacements in their car names. (Just look at today’s Mercedes-AMG V-12, which still displaces 6.0 liters but sits in the nose of a Maybach dubbed the S650—or look at the name of essentially any BMW.) This embiggening pushed the hand-built M120 V-12’s power output from 394 horsepower to just under 500.
Those 70-badged models were conversions handled by AMG, but fundamentally all started life as SL600s that customers then paid AMG crazy money to boost. (Estimates peg the cost of the engine upgrades alone at some $40,000 in 1998 money—this on top of the insane cost of an SL600 and the extra-cost AMG styling bits, and despite AMG offering a turnkey SL60 option.) Later, Mercedes and AMG would team up on a more factory, even more powerful R129 SL-Class conversion for the V-12, the SL73. As you might have surmised, the more muscular SL73 came with a 7.3-liter version of the M120 V-12 engine that produced 525 hp.
What more could you want? The SL73 combines the timeless lines of Bruno Sacco’s R129 SL with a huge, crazy powerful V-12 engine in a hedonistic exercise seemingly perfect for speeding toward Y2K and the dot-com bubble. It was an exclusive experience. Mercedes-Benz lacks concrete production information on the SL73, mostly because during the car’s 1995-2001 run, AMG was still a semi-independent outfit and its record-keeping left something to be desired, or something. In any event, the best estimates place total construction at about 80 of these huge-engined SLs. To this day, the SL73’s engine remains the biggest V-12 ever fitted to a roadgoing model, and it lived on in 7.3-liter guise in the Pagani Zonda supercar.
Why bring this SL up now? Mercedes is on the cusp of redesigning its iconic two-door, and the regal model is set to return to its sportier origins under AMG’s watchful eye. Will the V-12 be a part of that plan, to keep alive the 12-cylinder lineage running through factory SLs since the R129? Nope—the outgoing SL65 and G65 SUV marked the end of the line for V-12s within AMG’s lineup, and while there’s no way we’ll ever see a naturally aspirated, big-displacement V-12 like the SL73’s again, we can look forward to another ludicrously powerful “73” from Benz’s three-letter performance arm: the upcoming electrified eight-cylinder SL73e.