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Gas only, please: AMG won’t challenge BMW M with performance diesels

AMG 5.5 engine cutaway

Mercedes-Benz AMG will not produce diesel cars, despite rival BMW M’s recent announcement that it would, the German tuner told Autocar.

The head of AMG, Ola Kallenius, said diesels would compromise AMG’s mission of building high-performance versions of Mercedes luxury cars.

“The technology of performance gasoline engines is converging with diesel tech. Direct injection, downsizing and turbocharging are all having an effect,” Kallenius said, using AMG’s new 5.5-liter twin-turbocharged V8 as an example. This engine is replacing a naturally aspirated 6.2-liter V8 in AMG’s “63” models, such as the CLS63 AMG.

“We looked at diesel a few years back, but petrol engines have obvious benefits of sound, weight, agility and response,” Kallenius said. AMG did build one diesel car, the C30 CDI AMG, based on the C-Class, from 2001 to 2004, but with only a 3.0-liter five-cylinder engine and 228 hp, it was hardly a screamer.

While diesels have proven themselves at the 24 Hours of Le Mans endurance race, they do have several drawbacks when it comes to street performance. Because of the more violent combustion of fuel, engine parts need to be built with extra strength, which adds weight.

Diesels also don’t work well at high speeds; they have a lot of low-end torque to get a car off the line, but not a lot of horsepower to keep it going (which is why nearly every diesel has a turbo).

The sound of a car’s engine is more subjective, but anyone familiar with the clatter of a school bus knows the challenge any carmaker faces in making a performance diesel sound cool.

Mercedes AMG and BMW M are the in-house tuners for their respective companies, specializing in low-volume sports cars and performance versions of regular cars. Like their parent companies, the two share a rivalry as an intense as Ford versus Chevy.

AMG is known for taking a shotgun approach to the rivalry, producing tuned versions of every Mercedes from the SL roadster to the G-Class SUV. M, in contrast, sticks to core models like the M3 and M5.

The diesel decision changes that pattern. M’s engineers broke several of their cardinal rules when they built a pair of turbocharged SUVs, the X5M and X6M, and added turbos to a smaller engine in the new M5. Then they announced that they would build (Europe-only) diesel versions of the 5-series, X5, and X6, all with automatic transmissions.

AMG will keep things simpler, switching a 6.2-liter V8 for a 5.5 and limiting expansion of its (admittedly large) range.

Now, M is starting to look like the experimenter and AMG the stalwart. AMG is banking on one sustainable performance solution, while M is risking its reputation on another. Every rivalry has its limits, apparently.