Mercedes AMG's latest A45 made headlines last year for a variety of reasons, not least among them was its prodigious powerplant. Its new 2.0-litre, four-cylinder engineproduces 387hp in standard form and a massive 421hp in S guise, while producing 370lb ft between 5,000-5,250 rpm. In this way, the M139 is able to haul an A45 S from 0-62 in 3.9 seconds and on to a top speed of 168mph.
To wring that kind of performance out of such a small unit, AMG left no component untouched. The new twin-scroll turbocharger contains roller bearings to minimise mechanical friction, as well as an electronically-controlled wastegate, allowing for more precise and flexible control of the charge pressure, which can reach a maximum of 2.1 bar. It also benefits from a divided turbine housing and exhaust manifold, which allows the exhaust flow to be fed to the turbine separately, preventing the individual cylinders from negatively influencing each other.
The alloy cylinder block is said to be as resilient as that of a diesel motor, meanwhile, withstanding combustion pressures of up to 160 bar. It's paired with an all-aluminium crankcase, lightweight forged steel crankshaft and forged aluminium pistons, as well as a new 16-valve cylinder head with larger, variably controlled valves and two-stage fuel injection. The cylinders themselves are lined with Mercedes-AMG's F1-derived Nanoslide coating, giving them a mirror-like surface twice as hard as a conventional cast-iron liner.
Once assembled, this slew of techno babble and marketing bumf combines to create a truly remarkable power plant. One so good, in fact, that we included it in our list of the six best four-cylinder engines just last week. "A monstrous power unit," Matt called it, praising its incredible response, mighty mid-range and top end enthusiasm and concluding that it was, "undoubtedly a four-cylinder engine we'll be talking about in another 30 years' time."
Given all that, it may be hard to see why anyone would need more from their M139, but that hasn't stopped the engineers at Race Chip, who've gone and found a path to nearly 500hp. The below video details their methods (with an explanation of the tuning process itself beginning around the 6:45 mark) as they work their way to 491hp and 406lb ft of torque. Then, of course, there's the obligatory Autobahn run to sample the results. We won't steal the guys' thunder when it comes to the difference in 100-200km/h sprint times, but let's just say the results seem to speak for themselves.
Check out the video and let us know what you think about the A45's new power bump in the comments below.