Mercedes-Benz AMG A45 review

The most powerful hot hatch in series production. Well, until Audi puts the bit between the RS3’s teeth once again. But of course it is. Ding-dong, seconds out, round one, the A45 is the bone-cruncher-in-chief of the hot hatch power wars. And now all-new from the ground up.

The first A45 appeared in 2013 with 355bhp, and proceeded to more than double AMG’s sales target. Plus spawn variants: GLA crossover, CLA saloon, CLA Shooting Brake estate. The same will happen this time – the business is too good for it not to. The new one copies the 4WD, 4cyl turbo template but that’s about it: I ask Ralph Illenberger, AMG’s head of engine design if anything has been carried over, “yes, two bolts I think”. I’ll talk more about the engine, but before I get carried away, here’s what else you need to know.

As with other AMGs, the A45 now comes in two variants, plain A45 and A45 S. The latter, with an extra 33bhp, more standard kit, bigger wheels (19s not 18s), larger exhaust pipes, double the number of diffuser fins, bigger brakes, variable driving modes etc, is the only one coming to the UK. It’ll cost around £50,000. The CLA saloon goes on sale at the same time, costing about £2,000 more and delivering an almost identical driving experience: the hardware is the same for both cars (barring a tiny adjustment to the rear track width), the software tweaked to give the CLA a moderately less hardcore outlook.

The body has been majorly reinforced with a new shearing plate under the engine, a strut-mounted cross brace, diagonal bars across the front and rear underbody to support the subframes and inserts in the front wheelarches that connect the side members to the A-pillars and stop deformation under suspension compression. That’s quite a set-up.

Where the old car had a relatively crude 4WD system (front drive until it detected slip), this is much more sophisticated. The system takes information from everywhere: yaw sensors, steering angle, throttle, that bottle rolling around in the footwell, then distributes it (typically 50:50) between the axles. At the front a mechanical slip diff distributes power to either side, but at the rear it’s fully electronic: a pair of sophisticated clutch packs can send 100 per cent to either wheel. No 4WS, but the effect is similar. Drift mode, available if you maximise every setting and put the ESP to sleep, neatly limits torque to the front axle provided you’re giving it maximum sideways attack with the steering and throttle.

Now, this engine: it’s hard to consider a humble four cylinder as being very specialised, but keep that in mind as I tell you about it. It’s been turned through 180 degrees, so the intake is on the front, exhaust and single turbo on the back, helpfully shortening the tract lengths and lowering the engine height at the front, allowing a more aerodynamic bonnet line. Now consider the heat build up. Forget the hot-vee V8, Illenberger refers to this as ‘hot-back’ as exhaust and turbo sit cheek by jowl.

The cooling is unbelieveable. The turbo is water, oil and air cooled, with the latter ducted through an intake behind the grille, under the engine cover, and then down past exhaust and turbo and out through an opening left purposefully in the floor. The heat-shielding is considerable. There are three water pumps: electrically driven for the intercooler and cylinder block, plus a beefier mechanical pump for the head. That last can pump 280 litres of water per minute – over twice the flow of a standard car. The intercooler has to get inlet temperatures down from 200 degrees to 50. When it can’t cope it’s able to call on the cabin air conditioning system for help.

The engine block is all new and used nowhere else. It’s able to withstand combustion pressures of 160 bar – as tough as a diesel block, basically. Illenberger admits to having considered twin turbos and both turbo and supercharger layout before dismissing both for packaging reasons. Apparently AMG boss Tobias Moers’ eyes widened when Illenberger went in and stated that he thought he could get 415bhp from a single turbo 2.0-litre with the right power characteristics, response, emissions and so on. The twinscroll blower, running on roller bearings, has two separate air feeds, from cylinders 1-2 and 3-4. It pressurises to 2.1 bar.

Speaking of power characteristics, these are fundamentally changed. In the old car torque peaked at 2,250rpm and plateaued across to 5k. To feel more naturally aspirated and give you a reason to hold on to each gear, maximum torque (369lb ft) now doesn’t arrive until 5,000rpm, the delivery ramping up through the mid-range, rather than jumping at the bottom end and then simply sustaining.

Other stuff: there is a cabin sound generator which takes its cues from a sensor in the exhaust, the gearbox is an eight-speed multi-clutch DCT, it weighs 1,550kg, promises 0-62mph in 3.9secs, a 167mph max, plus 34.0mpg and 189g/km of CO2. It’s a very different beast from the AMG A35 that appeared last year, using an AMG-tuned version of a 2.0-litre Merc unit. The current A-Class has majored on design and technology. Can the full-house AMG take the fight to the Audi RS3 and BMW M2 and get the focus back on the driver?

The last A45 was a big sales success. So Mercedes-AMG has done what it does best: invest heavily in the R&D of its replacement. The 415bhp engine, the 4WD system, body stiffness, suspension, the electronics that support everything – all are highly impressive and very well integrated.

It is a very particular type of car: a bombastic hatch, big on speed and extrovert gestures, lacking a little in delicacy and adjustability. Leave that to coupes such as the BMW M2 or Alpine A110. The A45 has a different brief: to go fast and have fun. That aligns it precisely with the Audi RS3, a car that is both less talented and less charismatic. The A45 has a pretty big sweet spot: it looks good inside and out, operates unobtrusively when you don’t demand much, and goes properly feral when you do.