Though there were at least 16 made during various stages of development, Mercedes-Benz’s C111 remains frustratingly unattainable even as we approach the 50th anniversary of its unveiling next year. Conceived as a rolling laboratory to test emerging tech including multilink suspension, ABS, turbocharging, and perhaps most memorably–Wankel rotary engines–the C111 has been a dream car for generations of enthusiasts, summed up succintly by Mercedes themselves as an, “experimental vehicle, super sports car and style icon.”
Development began as early as 1967, and while it’s often repeated that the project’s goal was to produce a successor to the legendary 300SL gullwing of the previous decade, Stuttgart themselves claim this simply isn’t true, stating, “From the very start, the C 111 was conceived purely as an experimental vehicle. One of the objectives was to test the use of glass-fibre-reinforced plastic for automotive bodyshells. The car was, in addition, to be used for the testing of a new engine concept: the rotary piston engine designed by Felix Wankel.”
Though that seems pretty cut-and-dry, things become a bit more complicated when 1965’s SL X is taken into consideration. Though it never received its planned mid-mounted V12 engine and remains today in Mercedes’ incredible Stuttgart museum as a static display, the beautiful, gullwinged, Giorgio Battistella-styled (under MB Design Chief Paul Bracq, who defined MB’s 1060’s and 70’s design language) concept was initially considered for production as a range-topping SL model.
While the SL X unfortunately never had an opportunity to become one of the world’s very first mid-engined production cars, it clearly played a large role in defining the layout of even the earliest C111 prototypes as shown above.
Introduced at 1969’s Frankfurt International Motor Show as the C101, the car’s name was soon changed to C111 due to a copyright claim wherein Peugeot asserted rights to all three-digit model names with a zero in the middle–the very same objection was first heard by Porsche a few years earlier during launch of the 901/911.
Refined by Bruno Sacco (who worked under Bracq before replacing him in 1975, continuing as MB Styling Chief until 1999), the C111 was a masterful piece of industrial design, incorporating seemingly disparate themes plucked from existing Mercedes-Benz products–mostly conservative sedans–with a distinctly low-slung and exotic profile that would come to define the emerging supercar genre as a whole.
Despite this entirely new frame of reference, the car was unmistakably a Mercedes-Benz, featuring clean, uncluttered lines, neatly integrated lighting, and the overall appearance of a vehicle formed as much by function and efficiency as by raw emotion.
As a rolling laboratory for the development of new automotive technology, C111’s were fitted with a range of engines including V8’s and turbodiesel five-cylinders, though are probably best remembered for their two rotary powerplants. The first of these was a triple-rotor unit displacing 600cc per chamber and producing a healthy 280 HP, enabling sub-five-second 0-60 MPH runs and a top speed of 161–hugely impressive for the time, and still more than respectable even today.
Brakes came from the mighty 300 SEL 6.3, and cabin styling–much like the exterior–was somehow very different from that seen in contemporary MB production models but still recognizable as sharing the same corporate DNA.
A larger four-rotor, 350 HP Wankel was soon fitted, shaving a few more tenths from 0-100km/h runs and reportedly enabling 186 MPH flat-out. Read more about these prototype Mercedes-Benz rotaries here in an earlier Technically Interesting feature dedicated to Dr. Felix Wankel’s own personal, quad-rotor-powered R107 SL, as well as MB’s secret fleet of W113 Pagoda SL’s used during early 1960’s rotary road testing.
By 1971 MB’s management decided to stop all rotary production, as despite having reached a high level of operating refinement, output and reliability, key C111 project engineer Dr. Kurt Obländer was certain that relatively poor fuel economy was simply inherent to Wankel engines, with no real workaround, recalling, “Our four-rotor engine with gasoline injection represented the optimum of what could be reached with this engine concept. The multi-rotor design called for peripheral ports for the intake-air and exhaust-gas ducts. We were able to solve the difficult problems in engine cooling and engine mechanics by technical means. But the main problem of the concept, its low thermodynamic degree of efficiency, remained. Due to the elongated, not exactly compact combustion chambers, fuel economy was poor, resulting in high fuel consumption and unacceptably high pollutant emissions. These drawbacks were inherent in the design principle.”
Ever-tightening emissions and fuel economy standards saw the low-slung orange testbed refitted with an early version of the marque’s now-legendary OM617 3.0 liter diesel five-cylinder, a switch that prompted a slight change in name as well. Now called the C111-IID, the car’s project engineers boosted the five’s standard 1974 240D-spec 80 HP to 190 largely via fitment of a turbo and intercooler.
The top image shows an earlier, three-rotor C111 I on a steep-banked curve with three standard production Benz saloons, including a 250, 300 SEL 3.5 and 300 SEL 6.3, while the bottom depicts a C111-IID during a break from setting 13 diesel speed and endurance records at Nardo in June, 1976, one of which entailed circling the massive 12.5km banked test circuit for an hour at an average speed of 253.770 km/h, or roughly 158 MPH. Curb weight had steadily increased from ~2,400 pounds for the early triple-rotor C111 to just under 3,000 for the IID, though performance was still very good for the time, with 100 km/h or 62 MPH dispatched in 6.5 seconds and a top speed of 173.
In pursuit of even more broken records, MB introduced the C111-III the following year, though in reality the car shared virtually nothing with its predecessors, utilizing a longer wheelbase, narrower track, concealed wheels, and heavily revamped bodywork delivering a super-low drag coefficient of just 0.183. In case you’re interested, one of them is for sale–some assembly required–over here.
Here Jay Leno hosts a C111 running a corporate 3.5 liter M116 V8. Fitted in 1970 with a largely standard, 200 HP unit as first seen in the 280SE 3.5 beginning the previous year, the car’s main role was to provide direct performance comparisons with its Wankel-engined counterparts.
We’re big fans of Jay and enjoy seeing him take the car for a spin, but unfortunately Mercedes hasn’t yet reached out offering BaT a go. As close as the rest of us could ever hope to get would involve snagging one of the 30 Isdera Imperator 108i’s between 1984 and ’93, but really that’s not very close at all.