Next A45 will be the hot-hatch king

Mercedes-AMG is set to astonish its rivals with a 310kW, 2.0-litre engine that is easily the most powerful production four-cylinder ever made.

The new four-cylinder flagship turbo AMG engine will make its debut in the A45 hatch later this year, boasting power that would make it easily the king of hot hatches. It will probably also power other AMG 45 Series cars, like the GLA45 and CLA45.

It’s so powerful that it even outpunches Ferrari’s legendary supercar, the 288 GTO (which was powered by a twin-turbo V8), much less any other German or Asian four-cylinder.

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It’s more than 75kW stronger than the most powerful BMW production four-cylinder engine – and BMW M executives admitted that they had no plans to match the hot AMG.

Code-named M139, it out-thumps the most powerful version of the previous A45’s M133 by at least 30kW of power.

The M139 motor will come in two tune states, with the entry level still thumping out 285kW of power (and then there’s a 25kW step to the S Model version), while revving to 7,200rpm.

The torque is there, too, with the stock version delivering 480Nm, while the S lifts that to 500Nm.

The other four-cylinder rivals have no chance, falling up to 75kW off the pace, including the Subaru WRX STi, the Ford Focus RS, the Audi S3, the Volkswagen Golf GTi TCR and the Honda Civic Type R.

While we’ve yet to drive it, AMG insists the engine delivery is linear, with little to no turbo lag.

"We already set the benchmark in the segment with the preceding engine,” Mercedes-AMG chairman Tobias Moers said. “This fundamentally new four-cylinder presented us with the challenge of doing even better and we succeeded with a number of sometimes-revolutionary solutions.

“With the M139, we have once again impressively demonstrated the engine expertise of Mercedes-AMG. Not only is the output per litre unrivalled for a turbocharged engine, the high level of efficiency also demonstrates that the internal combustion engine still has further potential,” he said.

Just to highlight how different the M139 actually is, it has been turned 180 degrees around from the previous engine, with the turbo and the exhaust manifold at the back of the engine. The intake has been switched to the front.

The all-new twin-scroll turbocharger adopts roller bearings for the first time, just like AMG uses in the 4.0-litre biturbo V8 in the GT, to reduce friction and allow the turbos to spin  even faster.

With AMG feeding the cylinders with up to 2.1 bar of boost, the new engine uses an electronically controlled wastegate for more accurate response, especially at partial loads.

There’s a forged steel crankshaft, carrying forged aluminium pistons, coated in nanoslide linings, new piston rings and the sump has baffle plates to stop oil sloshing.