In a world where Mercedes-AMG has engineered a hot hatch with 310kW and 500Nm from just 1991cc, perspective is vital. You’d have to think that the masterminds behind the original VW Golf GTI would struggle to fathom a humble hatchback with the ability to monster supercars. Such is the rate of progress that the original Audi R8 V8 and 996 Porsche GT3 are both outgunned by the upcoming A45 S.
Of course, the headline act is the new, hand-built M139 engine. Its 310kW (in S guise, at 6750rpm) makes it the highest specific output of any series-production four-cylinder engine, generating a staggering 155kW per litre. Yes, the numbers beggar belief, with the 0-100km/h dash completed in 3.9 seconds and the hyper-hatch rocketing to an electronically limited Vmax of 270km/h.
One of the biggest changes behind the new ‘shark nose’ is the fact that the 160.5kg four-pot has been swung around 180 degrees, with the exhaust manifold and turbo now just ahead of the firewall. The intake is now at the front of the engine, requiring less plumbing, and a lower bonnet improves aerodynamic efficiency.
Read next: 2020 Mercedes-AMG A45 S preview
The heavily boosted 2.0-litre four-cylinder engine runs a bore increased to 83.0mm, while the stroke remains at 92.0mm for a swept volume of 1991cc. The compression ratio has been raised to 9.0:1, while the twin-scroll turbo pumps 30.5psi (2.1bar) of pressure into friction-reducing Nanoslide-coated cylinders. The turbo runs at an efficient operating temperature thanks to oil and water cooling; the radiator cops its fresh air via bonnet ducts and the engine cover. Boost pressure is monitored with an electronic wastegate, while two-stage fuel injection is a first for a high-performance four-cylinder.
According to AMG, the power delivery is now more like a naturally aspirated engine. The torque curve has been bolstered at lower rpm for improved throttle response, while there’s extra pulling power at the top-end due to the more free-revving tune. The maximum engine speed is 7200rpm and AMG claims the M139 is built to last at least 250,000km.
While other markets will receive a base-model A45 with ‘only’ 285kW and 480Nm, it’s not slated to make its way Down Under. Despite being down on power, the 0-100km/h time increases by only a tenth (to 4.0 seconds) and the top speed drops to an electronically limited 250km/h. The A45 S is expected to arrive in Australia in Q1 2020 alongside the CLA 45 S, which shares the A45’s mechanicals.
The outgoing A45’s polarising acoustics are beefed up with automatically controlled exhaust flaps. Depending on the drive mode, the soundtrack can go from “harmoniously discreet” to “emotively sporty”. Partial ignition interruption when changing up and auto throttle blipping when changing down adds aural theatre. Thankfully, the car’s extravagant pops and bangs aren’t dead.
However, it’s not just the engine that’s new, with AMG giving the rest of the drivetrain a significant overhaul. The fast-shifting dual-clutch gearbox gains a ratio to make eight, while Race Start is standard, aiding the feral 0-100km/h time. The AMG Performance-tweaked 4Matic+ all-wheel-drive system also does its bit for launch purchase.
Within the fully variable AWD system is a new differential for the rear axle, which has an electronically controlled multiplate clutch connected to each driveshaft. This means torque can be channelled left and right between the rear wheels as well as front to back for optimum traction.
For some, the system’s real benefit is that it’s allowed for the inclusion of a Drift Mode meaning the A45 will be able to vaporise tyres with typical AMG enthusiasm.
As for the chassis, AMG claims all A-Class components have been heavily revised, including a new aluminium wishbone design for the four-link rear setup that reduces unsprung weight. The strut front-end benefits from a wider track, too, and AMG claims the A45 S gains a newfound level of ride comfort, thanks to tri-mode adaptive dampers. An extensively reinforced body shell also increases rigidity.
There are six driving modes available to optimise the car’s bandwidth in all conditions. They include Slippery, Comfort, Sport, Sport Plus, Individual and Race. However, AMG Dynamics moves the game forward with Basic, Advanced, Pro and Master programs available for the ESC, allowing progressively unaided driving, provided the system senses driver inputs are within spec.
On the inside the dinky centre console gear selector has been ditched for the cooking model A-Class’s steering column wand. An AMG Performance steering wheel is covered in nappa leather/microfibre, while two 10.25-inch screens take care of the MBUX infotainment system (with AMG displays) and instrument cluster.
The exterior design doesn’t quite meet the engineering menace, but aggression can be found in the AMG-specific grille, with 12 vertical louvres, contoured headlights, and a powerdome bonnet. Flared wheel arches create space for the wider front track and 19-inch alloys, while the horizontal fins in the outer air vents increase the illusion of width. The intakes are functional for cooling and form part of the AMG aerodynamics pack, while the rear diffuser houses quad exhaust pipes.
As for its Aussie price, that’s unconfirmed, but given the extra performance (and the availability of the ‘lesser’ A35), we expect pricing to increase slightly on the circa $78K of the previous model. Around $85K is our tip.
Put into perspective, the original Golf GTI of 1976 mustered a mighty 81kW. Now, in 2019 the A45 S is mustering kilowatt counts that shame supercars of the recent past.