Aston Martin Rapide S

The spy photographers hiding around Aston’s Gaydon HQ probably wouldn’t bat an eyelid, but there are two telltale clues that this isn’t any old Aston Rapide. Firstly, the extra pipes that protrude from the exhaust tips are there to hook up to emissions testing equipment, a giveaway that this is a test hack.

Secondly, there’s a sneaky extra bit of plastic zip-tied to the grille. It tricks your eye into thinking this car still has a two -piece mouth, where actually it’s an all-new, one-piece gaping gob. And that’s all there is to suggest this is a trick prototype that the world’s not really supposed to know about. But this is the new Aston Rapide S, and its subtle bodywork – the new ducktail-style bootlid has been omitted for extra sneakiness – hides the fact that its 6.0-litre V12 has been tweaked to a hugely significant degree: from 350kW and 600Nm to 410kW and 620Nm.

The S won’t sit above the existing Rapide, it’ll replace it entirely, arriving midway through 2013 and should cost similar money to the current car. Aston will be hoping it can keep those with the cash out of the Porsche Panamera Turbo S, Ferrari FF and Maserati Quattroporte 3.8 twin-turbo.

When the Rapide landed in early 2010, the marketing pictures showed families and dogs frolicking around it. If you’ve ever sat in the back of a Rapide, you’ll know that it wants to be used as a saloon car in the same way that Robert Mugabe wants to relinquish power to the opposition: a six-footer sitting behind another six-footer will be caught in a pincer movement, his knees squashed up against the seatbacks and his headroom pinched by the swooping roofline. It’s also not amazingly easy to get into and out of the Rapide’s back doors with grace, and the boot is only slightly larger than a Vantage’s – and somewhat smaller than the new Vanquish’s.

The Rapide S, then, is a chance for Aston to shift the Rapide’s positioning: think of it not as a saloon-car substitute that can also do sporty, but more of a sports car that can also offer some of the practicality of a saloon car.

There was nothing wrong with the Rapide, it’s one of our best-balanced cars, the Sport mode is sportier, with punchier gear shifts when you’re really going for it, while we’ve made Normal more relaxed and improved the fuel economy by tuning the gear changes on the six-speed ZF auto.

Just like the Vanquish, part of the impetus for the revisions came from pedestrian-protection regulations, which Aston has tackled by adding perforated sides to the under-bonnet skin – you see them when you pop the bonnet; they help it deform more readily – and by lowering the V12 90mm. Crucially, dropping the engine has the added benefit of reducing the centre of gravity, improving the Rapide’s handling.

The effect ripples through the car. There are big changes for the front of the car, the pipes on the engine have to be looked at, and we’ve changed all the engine mounts – they’re crucial for the ride quality. They’re hydraulic and act like dampers for the powertrain – we’re looking to get rid of the powertrain resonance and get the mass of the powertrain working with the body. Here’s a good bit down here.

Most of the changes will be lost on Joe Public, but not the extra 60kW. Here, the Rapide S essentially follows the Vanquish, although Aston has given the bottom end more refinement than its sportier sibling: there’s variable valve-timing on the inlet and outlet cams, a revised block and new heads and enlarged throttle bodies. But it doesn’t have the Vanquish’s flat-valve airboxes, and they’re largely responsible for the range-topping sports car retaining 11kW of superiority.

You can complained that the Vanquish isn’t fast enough, but when you’re in the passenger seat of a Rapide S in sub-zero temperatures, it still feels like it can fire you down the road at an indecent rate.

In an era when the Germans have given us big kW gains coupled with tumbling CO2, the V12 only betters the old Rapide’s 355g/km by 1-2%, but points to the huge slab of extra power and that it’s a cleaner engine overall that also complies with strict new EU6 regulations.

For now, Aston has no stop/start system or trick eight-speed auto, nor any plans to offer four-wheel drive, as all its rivals do. But the Rapide remains a compelling proposition, with style, pace and a dose of practicality.