AMG's One - and Only - Turbodiesel

Mercedes Benz C30 CDI

German car manufacturers have either been embroiled in the Dieselgate scandal, or are the subject of rumours surrounding what's widely regarded as the beginning of the end for turbodiesel propulsion in road cars. You never hear AMG's name mentioned. Why?

Before that fateful afternoon of 18 September, 3 years ago, it appeared that turbodiesel cars could do no wrong. That all changed when Volkswagen was caught being ingeniously dishonest in the calibration of its turbodiesel engines.

Unlike AB de Villiers who retired silently, at his peak, the contemporary turbodiesel engine has been shamed into retirement – seemingly at its peak. The irony is deep and profound: diesels were supposed to be cleaner, more efficient and of late – no less given to performance. All the leading German brands, which are by implication the global automotive industry’s trendsetters, were convinced that turbodiesel cars would eventually eclipse the efficiency/performance coefficient of petrol.

Despite 'dieselgate' Audi is still pushing on with its latest performance diesel model, the SQ7. Is time running out for oil burners?

We’ll never know if that was indeed possible, as most German industry turbodiesel R&D has been ceased and repurposed to lithium-ion battery development. The scale of abruptness around turbodiesel’s descent into disfavour (at least as far as only passenger vehicles are concerned, for now) has blinded many analysts and car enthusiast. There is a belief that hysterical Californian emissions legislation, which remains tolerant to diesel-powered school buses, but has vilified German turbodiesel passenger car engines, surged an overreaction, which will ultimately lead to the end of turbodiesel engine development.

Speed. Efficiency. Emissions. Pick two.

How could the entire German auto industry have got it so wrong? Audi. BMW. Porsche. Mercedes. VW. Between the 5 of them, there is unrivalled engineering expertise, which surely would have anticipated an approaching diminishing return curve when outrageous promises were being made about the potential of turbodiesel engines?

As the automotive industry transitioned through the millennium, turbodiesel passenger cars were unambiguously being marketed for their efficiency and tax relief in a European marketplace where fuel was expensive and emissions taxes punitive. The range benefits of a sophisticated turbodiesel engine had immense potential in markets such as America, Australia and South Africa, where enormous driving distances over weekends and during vacations are the norm. But there was a problem.

It’s no fun cruising between heavy trucking traffic in a turbodiesel car if it is capable of achieving 1 000 km on a tank, but offers little in the way of performance. As the German brands started developing turbodiesel-engined cars that could produce true autobahn pace, the appeal of petrol engines became merely acoustic. Turbodiesels also dealt a lot more confidently with the mass burden of SUVs, due to their abundant torque delivery at low engine speeds, which meant 50ppm was the fuel of choice for the burgeoning class of SUVs subsequently popularised by all German manufacturers.

BMW M has fettled with a few turbodiesels in its time, here's the newest M550d.

BMW’s 3-stage turbocharged turbodiesel engine power X5 and X6 M50d derivatives and, late last year BMW revealed its quad-turbo M550d: 760 Nm and 0-100 kph in 4.4 seconds, with unparalleled cruising efficiency. It's a more usable performance car nearly everywhere, most of the time, than the more dramatic and expensive M5.

Audi’s done much the same, championing the agenda of high-performance turbodiesels, especially in its SUVs. It remains the only brand to have successfully marketed a turbodiesel-powered V12 SUV (the 2009 Q7, with no less than 1000 Nm of torque on tap) and SQ5 was a breakthrough high-riding performance car for Audi, being its first turbodiesel S-model. The current SQ7 boosts 900 Nm and boasts a claimed 0-100 kph time of 4.7 seconds. The credibility of those numbers is undeniable.

AMG as the outlier

Mercedes-Benz built a diesel-powered supercar concept once, a rather long time ago. In 1978 its futuristic C111 concept set an amazing speed record of 316 kph, powered by a 170 kW engine. If BMW and Audi have remained committed to the notion of high-performance turbodiesel over the last decade, why not Mercedes-Benz?

Think of it. There isn’t a single performance-orientated Mercedes-Benz turbodiesel-engined model on sale. Isn’t that curious? The explanation for this is solely attributable to AMG, who tried a 50ppm performance car – but only once.

The Mercedes-Benz C111 of 1978. A futuristic way of looking at diesel performance. 170 kW and a top speed of 316 kph.

AMG has an alarming predisposition for trying to make a performance car of just about any Mercedes-Benz. There is simply no other explanation for something such as an R63 AMG. This unrestrained enthusiasm spilled over into the world of turbodiesels with the C30 AMG, a true turbodiesel vehicle from Affalterbach, built on the W203 platform. Just as BMW’s triple- and quad-turbocharged M-car turbodiesel are considered true M GmbH vehicles, so too the C30 was an authentic AMG.

C30 wasn’t powered by a mere plug-and-play upgrade of the W203 series C270’s diesel engine. AMG invested in creating its very own 3.0-litre turbodiesel by adding lengthening the cylinder stroke, which boosted engine outputs to 170 kW and 540 Nm, coincidently a peak power number matching the C111 diesel supercar of the 1970s. Here was a C-Class diesel with 35% more power and great cruising economy. Success appeared certain.

Of all the cars AMG had a hand in, this R 63 AMG might just be the weirdest.

Despite its impressive performance, the C30 AMG was never evolved and quietly discontinued. The claimed 0-100 kph sprint time of 6.8 seconds might have been blistering for a turbodiesel-engined car in 2002, but it was still 27% slower than a comparable C32 AMG. C30 remains the only diesel AMG ever and perhaps an unrecognised symbol that at least some of Germany’s best engineers realised that turbodiesel technology was not everything it was being promised to be.

Mercedes-Benz allowed Audi and BMW free rein to establish S-line and M-division turbodiesel models, which it knew AMG would never be motivated to counter. That confidence must have stemmed from the knowledge that, ultimately, the turbodiesel story could not continue to deliver huge gains in power, throttle response and emissions compliance. It’s possible that AMG’s technical people anticipated that on a trendline of development, BMW and Audi would eventually deliver hugely sophisticated turbodiesel engines into a doomed market.

The AMG advantage

Like the diesel-powered C111 concept, C30 is a forgotten Mercedes-Benz. Despite not achieving much sales success and only being marketed for two short years (2002-2004), this (left-hand-drive-only, because of the limitations of its packaging) diesel AMG served a crucial purpose in dissuading Affalterbach’s finest engineers from investing precious time and technical resources on an engine type which is now a condemned configuration.

Audi and BMW have invested heavily to birth a line of immensely advanced turbodiesel engines which have edged terribly close to matching petrol-powered throttle response, but it has all been in vain. German legislation will soon nullify the appeal of any fast diesel-powered SUV or sedan in autobahn country and Europe’s other market of destiny for high-performance truck-fuelled vehicles, the United Kingdom, has seen buyers hastily abandoning the black nozzle at fuel pumps.  

The C30 lasted just 2 years in production and remains AMG's only foray into high-performance diesels.

Without German R&D investment, there will be no future high-performance turbodiesels. Porsche has already confirmed it is done with turbodiesel engines, which, by implication, means Audi will soon be too. BMW’s engineering spend will certainly return to matching petrol engines with a form of hybridisation for its future M-Division products, foregoing any future M-cars with a ‘d’ suffix. When AMG’s boss, Tobias Moers, was questioned about his division’s resistance to diesel the answer was simple: he’d rather spend the engineering resources on marrying petrol engines with electrification.

The turbodiesel trend rode a nearly unstoppable wave of torque throughout the last decade, although if you were a very astute industry observer the absence of diesel-powered AMGs always begged a contrarian question of scepticism. The drama around diesel has passed nearly unnoticed in Affalterbach. It’s also the reason why AMG is linearly powering ahead in global sales, unaffected by worrying about engines it might have to replace, unlike BMW’s M-division and Audi’s S-line product planners, who have parented a host of hugely impressive turbodiesel engines for which there might soon be no market for...

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