Renntech is among the top names in modifying Mercedes-Benz products. When the company claims to build the perfect 1992 600 SEL, it's worth paying attention. The result is the S76R, and the saloon has the most powerful naturally aspirated V12 ever to come from the company.

Renntech starts with the Mercedes M120 6.0-litre V12. It bores and strokes the powerplant to a massive 7.6-litre displacement. The new internals include titanium connecting rods and AMG cams. There are ported heads, beehive valve springs, and titanium retainers. Thirty-pound fuel injectors feed the petrol.

Gallery: RENNtech S76R 1992 Mercedes-Benz 600 SEL

The engine breathes through Renntech's own design for the airboxes. The exhaust gases go through equal-length stainless steel headers to sport catalytic converters and quad mufflers. Polished stainless steel exhaust tips poke out of the back.

With all of this work, the V12 produces 615 bhp (458 kilowatts) at 5,500 rpm. The peak torque of 703 pound-feet (953 Newton-metres) is available between 4,250 and 4,500 revs. This power lets the saloon reach 60 miles per hour (96 kilometres per hour) in the low-5.0 second range. The top speed is 155 mph (249 kph).

RENNtech S76R 1992 Mercedes-Benz 600 SEL
RENNtech S76R 1992 Mercedes-Benz 600 SEL

As a 1992 600 SEL, this saloon would usually come with a four-speed automatic. Renntech replaces this with an upgraded five-speed auto from a 1996 model. Plus, the tuner adds an OS Giken limited-slip differential. 

Beyond the engine overhaul, Renntech gives this S-Class restomod carbon-ceramic disks that measure 15.83 inches (402 millimetres) in front with six-piston callipers and 14.17 inches (360 millimetres) with four-piston stoppers at the back.

The suspension consists of shorter coil springs, and Renntech adds a second-generation adaptive damper system.

The tuned 600 SEL looks nearly stock on the outside. Renntech adds its own front splitter, boot lip spoiler, and louvred side mouldings. There's also an AMG ground effects kit. The sedan rides on one-off forged aluminium wheels that are 19 x 9 inches in front and 19 x 10.5 inches at the back. The company fits Michelin Pilot Sport 4 S tyres.

Renntech keeps the interior looking original but adds some modern upgrades. There are new seats, and diamond-stitched embroidery covers them. Much of the trim is carbon fibre, and the headliner is Alcantara. The company replaces the original bench seat with two, individually adjustable chairs. The stereo is now smartphone compatible.

Renntech built the S76R as a one-off, but you can also think of it as a proof of concept. The company is taking commissions for more. The company's announcement doesn't include pricing details. This seems like one of those cases where if you have to ask, you can't afford it.