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The World’s Only Sexy Diesel: C111- III

This Mercedes-Benz was not just a technological tour de force – it was also so downright sexy, that it quite possibly seduced the entire world into believing that diesel was the solution to all our worries.

Okay, so that’s perhaps a bit of an exaggeration. But at least it’s an effectful opening paragraph. And in all honesty, the C111–III is still the only diesel engined automobile in the whole world which I personally find really, really interesting. In fact, I do actually find it downright sexy!

The entire range of C111 prototypes were proudly exhibited at Techno Classica in Essen approximately a month ago. In some respects, it’s the diesel version (at the front of this picture) which was the most successful of them all.

Which explains why I was so thrilled about Mercedes-Benz having it on display at Techno Classica last month. It was even lined up among its entire family of C111’s just to showcase its origins too – and where the adventure ended. The C111 family is no doubt the most famous of all Mercedes-Benz prototypes, and they really did achieve much with the technology which was developed and tested in these fabulous machines: among others, anti-dive suspension geometry, mid-mounted engines and even Wankel engines. That was in the late sixties and early seventies – and then came the oil crisis and ruined everything. The biggest disadvantage of the Wankel engine was of course its fuel economy – or lack of – and it appeared that the whole C111 experiment would thereby be killed off by the oil crisis.

But no. Instead Mercedes-Benz cleverly turned a bad situation to their advantage by equipping their super sportscar prototype with a diesel engine from one of their road cars – the biggest they had of course; the 3-litre 5-cylinder from the 300D. Only while doing so, they also bolted a rather large turbo to the diesel engine which more than doubled the output from a mere 80hp to all of 190hp. And with that, they immediately set out on a hunt for records with their new diesel sportscar: the C111-IId. This was of course during the mid seventies where the diesel engine still had a pretty poor image and was mostly associated with tractors, commercial vehicles and perhaps at best, slow and noisy taxis. But Mercedes-Benz had a plan which involved launching a turbo-charged version of their strongest diesel engine in their range-topping luxury S-class.

The most famous C111’s are the orange cars which were all “Technologieträger” for Mercedes-Benz. One was equipped with a diesel engine and subsequently set the first records for Mercedes-Benz.

In order to aid such a ludicrous idea towards success, Mercedes-Benz figured they would start by giving the diesel engine a solid image boost. They succeeded too: in 1976, four drivers maintained average speeds beyond 250 km/h – equating to 155 mph – in a number of disciplines with the C111-IId. This great achievement was performed at the brand new Nardo test facility in Italy, where the Mercedes-Benz smashed records on both shorter distances but also on the long ones such as 5,000 km, 10,000 km and 10,000 miles. With its 190hp, the topspeed of the C111-IId was approximately 260 km/h, so the four test drivers would have clearly kept the accelerator well and truly buried for almost three days! Amazingly, the Mercedes-Benz performed faultlessly.

The 5-cylinder diesel engine was borrowed from the 300d and then equipped with a turbo charger. Here its seen in the first record car – the C111–IId.

Even so, the white-cloak-wearing Mercedes-Benz engineers knew that there was potential for even more, because as you can see, the bodywork of the record-setting C111-IId was virtually identical to the earlier prototypes. Granted, much work had in fact been put into the aerodynamics of the early C111’s as well, but they had still been developed largely as road going sportscars which would be functional among other traffic rather than being developed for speed records. So what could be achieved if regular considerations which apply to road cars were canned and the car instead optimised without compromise for pure high speed records?

The original shape was so right that much more extreme methods were required to find further aerodynamic improvements.

Much, MUCH further is the answer. With the new C111-III, they took their studies on aerodynamics to the next level by developing not only a new body for the car, but also a brand new chassis. As a result, it was both lower and narrower in order to achieve a smaller frontal area and as low a drag coefficient as possible. But also the smaller details were looked at in order to make it as slippery as possible, so the C111-III could cut through air like a hot knife through butter. Previous C111’s had all been equipped with wide low-profile tyres – especially on the rear – but that wasn’t the case for the new third incarnation as it made due with very narrow tyres both front and rear. It just wasn’t visible as all four wheel arches had been entirely covered by wheel slats. Practicalities such as the turning diameter had been sacrificed in favour of aerodynamics. But despite aiming for a low drag coefficient, there was still much attention paid to directional stability as this would be essential for the drivers that would be travelling at high speed for several days: A vast vertical fin was placed on the rear of the bodywork. The final result was a drag coefficient of only Cd=0.183!

Almost 5.4 metres long and shaped by the wind.

In comparison, the increased power output of the engine was probably less influential. Nonetheless, the Mercedes-Benz engineers weren’t leaving any leaf unturned. While the engine was still based on the 3-litre diesel from the 300D, it had now been fettled even further to deliver all of 230hp. The C111-III had also in effect become a single-seater as the area normally equipped with a passenger seat was now occupied by a broad duct leading vast amounts of cold, dense air from the front of the car and straight into the turbo engine sitting just behind the cabin.

This sight might seem familiar to many Mercedes-Benz diesel owners, but plenty of forced induction boosted output to all of 230 horsepower.

And it worked! In April 1978, Mercedes-Benz initiated their new speed record attempts, and by the time the smoke had settled again, the C111-III diesel racer had set a new set of very impressive records – leaving a huge margin to the previous records set two years earlier.

100 km – 316.484 km/h
100 miles – 319.835 km/h
500 km – 321.860 km/h
500 miles – 320.788 km/h
1000 km – 318.308 km/h
1000 miles – 319.091 km/h
1 hour – 321.843 km/h
6 hours – 317.976 km/h
12 hours – 314.463 km/h 

The absolute topspeed was measured at 325 km/h – equating to 202 mph – and it took a full lap of the 12 kilometre long Nardo track to reach it. But the most impressive part was perhaps the fuel consumption during the record attempt which was 6.25 km/l – equating to 17.65 mpg. Okay, at first this might not seem a particularly impressive figure, but bear in mind that it was achieved at well beyond 300 km/h and with the pedal to the metal! And it was with technology which is now all of 41 years old. Mercedes-Benz would no doubt also focus on the fact that it was achieved with an engine which was taken out of one of their road cars, and that the new technology applied to this engine would later be available in their road cars – albeit, only with 125hp. All of which really did help the general image of diesel engines among the public (at least if it were a Mercedes-Benz diesel – it would still take several years before any competitors caught up). Mercedes-Benz were not just the fastest, but they were also the first to introduce the turbodiesel engine to regular road cars. From there – as we all know – the technology and not least the market segment practically exploded exponentially until more than 50% of all Germans drove a turbodiesel of some sort.

Many years later, the technology was found to have other shortcomings, among others that the right driving pattern was essential for diesels to be advantageous. But if you travel very long distances at a sustained very high speed, the C111-III delivered the answer: Turbodiesel is the perfect engine for the job.

This ultra-efficient Technologieträger communicated the strength of diesel with typical German effectivity. If it’s really a significant contributing factor to all of us later being saddled with the diesel car, then that is truly a heavy burden for the C111-III to carry on its narrow shoulders. Where the delusion surrounding diesel technology should otherwise stem from is a good question.

But regardless of how we feel about diesel cars today, it was a genuine pleasure to witness the stunning speed record car in the flesh. It confirmed to me that the Mercedes-Benz C111-III is still the world’s only truly sexy diesel.

Just for good measure, it’s worth noting that the predecessors which were fuelled by petrol were naturally also rather sexy.


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