Mercedes-AMG A45

A compact sports hatch with 188bhp per litre…

The McLaren 675LT provides 666bhp from an engine displacing just 3.8 litres, each litre of which being therefore responsible for the provision of 175bhp. Pretty impressive, but perhaps not so far from the realm of expectation for a limited-edition, track-focused McLaren costing £260,000. More surprising is when that output per litre is beaten by a five-door, five-seat hatchback costing less than one sixth of the price. But that is what we have here with this renewed 376bhp, Mercedes-AMG A45, whose litres provide 188bhp each.

That’s a 20bhp improvement on the previous, hardly slothful A45 and I wonder whether Mercedes would have felt the need to make the change had the car not been eclipsed in power terms (if few others) by Audi’s new RS3. But there will always be some who will insist on having the most powerful car in whatever class they are shopping in, so I guess we should not be too surprised by Mercedes’ willingness to take advantage.

The fact Mercedes is able to squeeze so much power from such a tiny engine and leave it so mannered is altogether more surprising. A few years ago I saw one of these engines screaming away on a test bed during one of those tests where they put a metaphorical brick on the throttle and come back a week later to see what’s happened. The exhausts looked like the molten core of the earth but, as the man proudly told me at the time, “We just can’t seem to break it.” So they gave it some more power and, now, even more again.

Now this hatchback will out-accelerate a brand-new twin-turbo Porsche 911 Carrera S even if you equip said Porsche with paddle shift gears and launch control. And because of the context in which such crazy thrust arrives, it really will make you gasp. On a private facility I informally timed it from 0-100mph in less than 10sec, the first time I have ever known any such car get close to single digits over such a measure.

So it’s fast, but is it funny? More so than the car it replaces, which Mercedes appeared to think so quick it had better be tuned to understeer everywhere just in case it all got too much for the driver. The A45 feels agile now and quite engaging, even if ultimately it lacks the pure chassis fluency of a BMW M235i or even a VW Golf R. Both are far slower and less powerful but, to me at least, more pleasurable cars to drive fast.

But if what you really want is the ultimate pint-sized rocketship, a quite practical, surprisingly frugal, tolerably comfortable, adequately refined point to point missile, its only true rival for now is the Audi RS3. It’s a better bet than that, and by far.

Factfile

Price £39,960

Engine 2.0 litres, 4 cylinders, turbocharged

Power 376bhp@6000 rpm

Torque 350lb ft@2250 rpm

Transmission seven-speed automatic, four-wheel drive

Weight 1480kg

Power to Weight 242bhp per tonne

0-62mph 4.2sec

Top speed 155mph

Economy 40.9mpg

CO₂ 162g/km