It just takes some updated software to get these gains.
The Mercedes-AMG M139 2.0-liter turbocharged four-cylinder is an absolute jewel of an engine because of its amazing output of 416 horsepower (310 kilowatts) and 369 pound-feet (500 Newton-meters). An interesting new video from the German tuner RaceChip offers a review of the mill in the A45 S and offers some insight into what's necessary to boost the output even higher.
RaceChip's tune pushes the engine to 484 hp (491.1 PS or 361 kW) and 399 lb-ft (540.9 Nm) of torque. The dyno shows this setup making 400 hp (405.3 PS or 298 kW) at the wheels, which equates to a driveline loss of 17.47 percent. RaceChip takes the upgraded hot hatch to the autobahn and finds that it can go from 62 miles per hour to 124 mph (100 kph to 200 kph) in 9.16 seconds.
Gallery: Mercedes-AMG A45 S RaceChip Tune
Even before the tune, the two guys from RacingChip have largely positive things to say about the A45 S. Despite having a massive turbo, the engine is quite responsive. One downside is that it doesn't sound quite as mean as the previous generation of the hot hatch.
RaceChip charges €699 ($751 at current exchange rates) for this upgrade. There's also a lesser version that adds 58 hp (43 kW) and 24 lb-ft (33 Nm) for €399.
If you want even more power from an A45 S then the folks at Renntech can help. The company can boost the output as high as 592 hp (442 kW). This requires fitting a modified turbocharger, exhaust, and engine software.