Mercedes-AMG has just announced an engine without a car to go with it. But it's the most powerful four-cylinder in the world, and we're pretty sure whatever cars it goes in will be very, very fast.
Four hundred and twenty-one horsepower. From two litres of displacement. That, Mercedes says, makes it the "world's most powerful turbocharged four-cylinder engine in series production." It's 211 hp per litre, which makes this the highest output per litre of any mass-produced road car built. Today or any other day that's passed.
It's an astounding figure. Look at the competition, and it's not even close. Bugatti's Chiron? A paltry 187.5 hp/L. McLaren Senna? 197. What about cars you can actually buy? The Volvo V60 Polestar manages 181. And yes, sharp-memoried readers, the Koenigsegg Jesko is expected to be a little higher. But it's not out yet, and they'll probably build fewer than 20. Whereas Mercedes-AMG will build plenty of these.
That 421 hp figure is for the S version of the engine, but the standard one manages a still whopping 387. With 369 lb-ft of torque for the S and 354 for the base.
How does Mercedes do it? It starts with rotating the engine's accessories. The turbo and exhaust have been moved to the rear, against the firewall. This allows more efficient ducting for intake and exhaust air, plus more cooling. The twin-scroll turbo ensures that cylinders aren't fighting each other to expel air. The turbo also adds roller bearings to reduce friction and let it build boost more quickly.
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A max of 31 psi of boost means that this engine is cramming massive amounts of air and fuel. Oil and water cool the turbo, but also fresh air directly from a vent under the hood.
The cylinders are lined with a coating called Nanoslide. Mercedes uses the process on Formula 1 engines as well as other AMG models. Mercedes-AMG has also optimized the valve sizes and angles for better flow.
Like other AMG engines, each of these will be assembled by a single technician. That process has been redesigned for more flexibility and to use more renewable energy, as well as make the process easier for the technician.
So where is this turbo four, which makes more power than most V8s, going to end up? Mercedes-AMG isn't saying directly, but they did say that it "will ensure agile performance for the compact models of Mercedes-AMG." They've also said that it will be replacing the M 133 engine, which was one of the previous power per litre champs.
So where was that engine? Making 41 hp less than the new one, it powered the CLA 45 AMG four-door 'coupe', the A 45 AMG subcompact hatchback that never made it to North America, and the GLA 45 AMG small SPORT utility/crossover. Which means that this is the engine you can likely expect in the new versions of those models. Especially since Mercedes-AMG has already confirmed that the A 45 will get more than 400 hp from a turbo four.