When Mercedes-AMG introduced the ‘45’ models with the last generation A-Class range with the world most powerful 2.0-litre, four-cylinder motor that could churn out 3around 380hp. While that number may be fascinating at the time, the sales numbers actually didn’t as the premium asking price, even in Europe, forced people to check out the most trusted hatchback, the Golf GTI instead. Even if it didn’t have the most powerful 2.0-litre engine n the world. That statement didn’t last very long either because, with a little bit of turbo trickery and some hybrid induction, Volvo pipped it with their 2.0-litre, 400hp motors soon after.
Now, however, as Mercedes has introduced the fourth-generation W177 A-Class range, it had to receive the AMG treatment. However, it needed to be even more impressive than before. Which is why the new ‘M139’ 2.0-litre, 4-cylinder engine that will find its way in most ‘45’ badged AMG models will get 416hp and 500Nm of torque. I say most because that power output will be reserved for the ‘AMG 45 S’ models. The standard AMG 45 models will be tuned down to 382hp and 480Nm of torque.
Sticking with the aforementioned number of 416hp and 500Nm of torque, from a 2.0-litre, four-cylinder twin-turbocharged engine, allows it to reclaim the title of most powerful series production four-cylinder engine with a specific output of 210hp per litre.
The new M139 engine itself is a derivation of the M133 motor it replaces, however it is extensively reworked. The new motor is designed to deliver the free-revving response of a naturally aspirated engine. The torque is tuned to build up low down in the rev-range but in a more gradual manner while peak torque is set high up at around 5,000-5.250rpm. Peak power is delivered at 6,750rpm while the engine redlines at 7,200rpm for the ‘S’. For the standard 45 models, the peak output is delivered slightly lower at around 4,750 -5,000rpm
The achieve these numbers, Mercedes had to use high-strength, chill-cast, closed-deck aluminium engine block. The block is designed to manage diesel-like temperatures and peak combustion pressures which rates over 2,300psi. The engine features larger exhaust valves, two-stage fuel-injection system, twin-scroll turbo system which is cooled by water, oil, and air, the later directed from the grille by ducting and a specially crafted engine cover.