The world's most powerful hot hatch is on its way

The world’s most powerful four-cylinder engine is on its way to the new-generation Mercedes-AMG A45 hatchback.

The all-new 2.0-litre four-cylinder engine ups the ante over the already bonkers previous-generation engine, with a peak power output of 310kW (at 6750rpm) and massive torque pegged at 500Nm (at 5000-5250rpm). Those are the outputs for the new S version of the A45, while a lower-grade, lower-output engine will also be offered with 285kW (at 6500rpm) and 480Nm (4750-5000rpm).

You may have noticed that peak torque hits a lot higher than you might expect - and that’s on purpose, according to Mercedes-AMG, which says the “torque shaping” was done to achieve “a power delivery similar to that of a naturally aspirated engine for an even more emotive driving experience”.

If you’re wondering how that compares to the previous A45, the S version runs at a 30kW/25Nm advantage. It had 280kW at 6000rpm and 475Nm from 2250-5000rpm. As you can see, the new engine - codenamed M139 - will be a more free-revving engine, and indeed it has a maximum engine speed of 7200rpm.

Tobias Moers, chairman of Mercedes-AMG, said the new, most powerful series production four-cylinder engine in the world is a vital step forward over the existing benchmark setter.

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“We already set the benchmark in the segment with the preceding engine. This fundamentally new four-cylinder presented us with the challenge of doing even better,” said Mr Moers.

The new engine - which continues to be handmade under the brand’s “one man, one engine” philosophy - comprises one twin-scroll turbocharger, and runs a compression ratio of 9.0:1.

The charge pressure maxes out at 2.1 bar for the S model, and 1.9 bar for the regular version, and it uses an electronic wastegate to “allow charge pressure to be controlled even more precisely and flexibly while optimising responsiveness”. The water pump also uses electric management to operate independent of the engine.

The all-new Mercedes-AMG A45 hot hatch that the new M139 engine will be fitted to is still yet to be revealed - and so are further details of the drivetrain.

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But CarsGuide can reveal that the new model is set to see the introduction of an eight-speed dual-clutch automatic transmission, and yes, it will again be offered exclusively with all-wheel drive. 

AMG has teased the small car screamer, which also appears to have a new Drift Mode system allowing it a more rear-happy character.

Stay tuned for that - we’re sure it’ll be just as bolshy as its engine outputs suggest.

How much is too much for a hot hatch? Tell us your thoughts in the comments section below.