There are many ways that cars signal their interest in speed. Fat tyres with viciously spoked alloys, paint stripes down the bodywork, radiator grilles that resemble the wire fencing around a correctional facility - these are some of the traditional indicators that the vehicle you are looking at is uncommonly absorbed by the prospect of going fast.

None of those signs, though, rams the message home like the sight of an air intake over the engine. If a car is breathing through a gratuitous nostril halfway up its bonnet, you are perfectly within your rights to suspect that it has some unresolved issues surrounding acceleration and an appointment already in its diary for a meeting with the motorway police.

When it comes to gratuitous nostrils in cars, Subaru is right up there with the market leaders. The Japanese manufacturer of mass-appeal “performance” cars has been excitedly carving lumps out of the bonnets of its products since Damon Hill was no more than a twinkle in his father's carburettor, and certainly since well before the invention of ram-raiding. Nobody rivals Subaru for punching a hole in the front of a car and then forming a thick metal pout around it, so that it looks, from certain angles, like Mick Jagger in distress.

A “powerdome” is basically the automobile equivalent of the sleeveless shirt worn by Rafael Nadal. It implies that the car is so bristling with muscles that the conventional coverings alone cannot contain it. The engine is in the process of leaving the car vertically, and it's not waiting for anyone to finish fumbling around with the catch before it does so.

Subaru's flagship product in this area was always the Impreza - a heated-up hatchback beloved of thrill-seeking speed freaks and so unashamedly “wide” that it was frequently seen with gold-painted hubcaps. Except that last year, Subaru re-released the Impreza in a version that had no powerdomes anywhere, nor any gold hubcaps, looked as tame and as anonymous as any other family hatchback and came with a marketing campaign that emphasised (of all things) its safety while cornering.

Since when has there been room to wonder what Subaru is mostly in the business of building: borderline-legal monsters designed to leave a layer of rubber at every junction, or modest everyday vehicles, designed to go quietly about their innocent business? Or both at once? These confusions come charging together in the newly upgraded Subaru Outback.

The Outback has a hulking great powerdome and the pale staring eyes of the speed addict. But at the same time it's an estate car. Its boot space is clearly inviting you to head for the out-of-town shopping centre or set up business as a painter and decorator. Yet on account of the air-intake and what you remember about Subarus that you have driven in the past, you openly expect to depress the accelerator and join your dog in the boot, flung backward by the face-reshaping G-forces.

In fact, remaining both seated and in relative command of the steering wheel continues to be an encouragingly viable proposition, because the Outback is fitted with Subaru's first diesel engine - a shift of working principles so radical that betrayed petrol-heads may regard it as the equivalent of Bob Dylan going electric and fall over in shock. If Subaru is boasting about a car's “class-leading fuel efficiency figures”, the jig must be well and truly up.

The point is, though, that the Outback only looks like the kind of car that would go into a corner one way round and come out the other. As such, it seems designed to speak loudly to the responsible grown-up in whom the whooping boy-racer is dying hard. Yes, you've bought an estate because you realise that you are sufficiently encumbered to need one, but you haven't given up.

It's a properly robust, four-wheel-drive creation, though. For once, those thick bits of cladding on the sides aren't there simply to ensure that the paintwork doesn't get too badly scuffed when rubbed lightly against a suburban privet hedge. They are significant pieces of reinforcement, proposing a potential take-up for the Outback, not just with retired rally drivers but also among farmers with proper jobs to do. Do farmers love a gratuitous nostril? We're about to find out.

Subaru Outback 2.0 TD

Top speed: 124 mpg

Acceleration: 0-60 in 8.8 seconds

Average consumption: 48.7mph

CO2 emissions: 153g/km

Green rating: medium

One careful owner: Michael Eavis

In the glovebox: Fisherman's Friend

On the hi-fi: The Ting Tings

Bound for: Shepton Mallet

Buy it if: it's lambing time

Marks out of 10: 7

Price: from £21,495