Gather around, boys and girls, because Mercedes-Benz has just unveiled more performance versions of the latest W177 A-Class positioned above the A 35. This is the new Mercedes-AMG A 45 4Matic+, which comes in standard and S guises, mirroring the approach the company has taken with its larger V8-powered models (think C 63/C 63 S and E 63/E 63 S).

Under the bonnet, there’s a new 2.0 litre turbocharged four-cylinder engine dubbed the M139, and it replaces the M133 unit used for the previous W176-based A 45. The engine is unique to the A 45, as the A 35 uses an uprated version of the M260 (306 PS or 302 hp, 400 Nm) that is shared with the A 250.

Additionally, the mounting of the M139 sees it being rotated 180 degrees to ensure the turbocharger and the exhaust manifold are positioned at the rear. This creates space for the intake system to be placed at the front, providing better air ducting with shorter distances and fewer diversions – both on the intake and exhaust side.

Other highlights include an all-aluminium crankcase, forged steel crankshaft, forged aluminium pistons (residing within Nanoslide-coated cylinders), baffle plates for the oil sump, repositioned injectors and larger exhaust valves.

The M139 also sports port and direct injection, with the latter being used during lower loads where efficiency is prioritised. When maximum performance is needed, the second stage (port) injection is activated via solenoid valves, with the electronically controlled fuel supply operating at pressure of 6.7 bar.

There’s also the matter of cooling the thing, given the amount of power it makes (we’ll get to that real soon). An electric water pump supplements a mechanical one, and on the S-model, there’s a second radiator in the wheel arch to supplement the main one at the front. Cooling of the transmission oil is integrated into the engine’s coolant circuit, and is assisted by a heat exchanger mounted directly on the transmission.

On the “basic” model, the single twin-scroll turbocharger is boosted to 1.9 bar so the engine makes 387 PS (382 hp) at 6,500 rpm and 480 Nm from 4,750 rpm. This is already a step up from the M133 powerplant, which “only” made a maximum of 381 PS (375 hp) at 6,000 rpm and 475 Nm from 2,250 rpm.

Of course, the A 45 S 4Matic+ is the one that will draw in a larger crowd, as it offers 421 PS (416 hp) at 6,750 rpm and 500 Nm of torque from 5,000 rpm thanks to a higher charge pressure of 2.1 bar. An AMG exhaust system with a controllable flap can be found on both versions.

Performance-wise, the A 45 S is the quickest in a zero to 100 km/h sprint, taking just 3.9 seconds to do so. The normal A 45 is no slouch though, as it does the same feat only a tenth of a second slower at 4.0 seconds. However, the S-model tops out at 270 km/h right out of the factory, while the base model needs the optional AMG Driver‘s Package to do the same as it is limited to 250 km/h in stock form.

These figures, Mercedes-Benz claims, makes the M139 the world’s most powerful turbocharged four-cylinder engine manufactured for series production. On the topic of production, the engines are individually handbuilt as per the company’s “one man, one engine” principle.

The M139 is paired to an eight-speed AMG Speedshift DCT 8G dual-clutch transmission, as well as an AMG Performance 4MATIC+ fully-variable all-wheel drive system, whereby the latter comes with some “secret sauce” called AMG Torque Control.

Found in the rear axle differential, there are two electronically controlled multi-disc clutches, each connected to a rear axle drive shaft. This allows the engine power to be fully distributed between the front and rear wheels, as well as selectively between the left and right rear wheels.

As such, the A 45 S, which gets the AMG Dynamic Plus Package as standard (optional on the base model), comes with a dedicated Drift mode. Selectable with Race mode engaged, it allows you to pull off spectacular powerslides when activated, provided that the ESP is deactivated, the transmission is in manual mode, and you know what you’re doing.

Behind the wheels are 350 mm brake discs and four-piston monobloc fixed calipers at the front, and 330 mm discs with a single-piston floating calipers at the rear. The optional AMG Dynamic Plus package (standard on the S-model) bumps this up to 360 mm/six-piston calipers front, and you can identify this by the red paint and black AMG logo – normal brakes are painted grey with white AMG lettering.

Efforts have also been made to reinforce the bodyshell, with an aluminium plate bolted underneath the engine to increase torsional rigidity at the vehicle’s front end. This is supplemented by a strut tower brace between the front suspension struts and additional reinforcing plates connecting the side members to the A-pillars to stabilise the front section. Diagonal struts at the front and rear of the underbody further improve rigidity.

The chassis specification includes McPherson struts at the front, and a four-link setup at the rear. Passive dampers are standard fitment here, but there’s an AMG Ride Control adaptive damping system available if you need more variability. Also present is a speed-sensitive, electro-mechanical power steering system, which provides a sport or comfort-biased feedback depending on the driving mode.

On that mention, you get six modes in the AMG Dynamic Select system that are linked to the powertrain, transmission, AMG Dynamics, exhaust system and chassis – Slippery, Comfort, Sport, Sport+, Individual and Race – last one being optional for the base model.

Within the AMG Dynamics menu, you can further vary the characteristics of the all-wheel drive system, steering and ESP according to four presets – Basic, Advanced, Pro and Master (standard on the S-model) – each assigned/configured to the aforementioned drive modes.

In terms of styling, there’s plenty of aggression on show here, starting with large air intakes on the jet-wing-profiled front bumper. A Panamericana grille acts as a reminder that this is the range-topper in the A-Class range, while flared wheel arches accomodate the wider front track.

At the rear, there’s a diffuser element in between the two round twin tailpipes, with each outlet measuring 82 mm each on the base model, and 90 mm on the S-model. The base car also gets smaller 18-inch light alloy wheels, whereas a 19-inch set is used for the more powerful version.

If it still looks a little too “tame” for your liking, there’s always the AMG Aerodynamic package that adds on a front splitter and canards, more diffuser blades, rear spoiler lips and a roof spoiler, all highlighted in high-gloss black. Different wheel designs, an AMG Night package and Silver Chrome package are other options.

Inside, you get a typical A-Class cabin, with the Mercedes-Benz User Experience (MBUX) infotainment taking centre stage, albeit with AMG-specific displays – Classic, Sport and Supersport. Various special displays can also be called up if you’re interested to know how many g you pulled in a corner, a stopwatch, temperatures, AMG Track Pace (telemetry logging), and more.

Sport seats and an are complemented by black Artico man-made leather and Dinamica microfibre upholstery, while lesser details like red accents on the air vents and red seat belts can also be found. The S-model takes things further with yellow highlights, including on the AMG Performance steering wheel.