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Mercedes-AMG unveiled the new M139 version of its 2.0-liter turbocharged cross-cylinder, and the maximum power is breathtaking. That's 416, or 40 more than stumped by the M133 engine that it replaces. This means that the M139 replaces the M133 as the world's most powerful four-bang engine. The 416 horsepower and 369 lb-ft version is for certain AMG models with the S logo; non-S versions will get a slightly detuned version rated at 382 horsepower and 354 lb-ft.
As remarkable as the power output is the way it is delivered. While the former M133 featured the typical square torque curve of a four-turbo, the M139 is designed to offer the feeling of free rotation of a naturally aspirated engine. The couple still rises quickly at low speeds, but the rise is more gradual and the peak torque (which is up 19 lb-ft from last year) is very high, ranging from 5,000 to 5 250 rpm, with a horsepower of 650 rpm. Redline is 7,200 rpm. (The torque of the non-S engine reaches slightly lower peaks, between 4,750 and 5,000 rpm.)
To achieve these new numbers, AMG began with a high-strength, die-cast, die-cast aluminum block that is strong enough to withstand maximum diesel-like combustion pressures greater than 2,300 psi. AMG's patented "Nanoslide" coating on piston liners reduces friction, as does the transition to 0W20 grade oil.
The cylinder head is a brand new design, with caps and injectors rotated 90 degrees from the M133 to allow larger exhaust valves. A new two-stage fuel injection system combines direct injectors that spray into the combustion chamber and secondary injectors located in the intake manifold.
The twin-scroll turbocharger now uses roller bearings to reduce friction and an electronic relief valve actuator for more precise control. The turbine casing is divided into two separate flow passages, each fed by a pair of cylinders. The double passages perform a function similar to that of exhaust manifolds of equal length, ensuring that the exhaust pulses of the cylinders do not interfere. The turbo is cooled by water, oil and air, the latter being directed from the grille by ducts and a specially shaped engine hood. The boost peak is slightly below 30.5 psi for the S engine and just over 27.5 for the base engine.
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