Bentley Continental GTV8

Why the new Bentley GT is all the better for downsizing its engine

Price: £110,000 approx
Engine: 3,993cc, V8 cylinders, 32 valves, twin-turbo, 500bhp
Transmission: Eight-speed automatic gearbox, rear-wheel drive
Performance: Over 180mph, 0-62 in 4.9 seconds, 24.0mpg, CO2 275g/km

If you are wealthy enough to own a Bentley Continental, then your car's consumption of expensive hydrocarbons may be of little concern beyond a distant guilt about burning the Earth's resources and the annoyance of having to stop to refill the tank. Bentleys have big petrol tanks, of course, but that's of limited help when the contents are consumed so rapidly. How would it be, then, if your Continental could travel 40 per cent further on the same-size tank? That would be very convenient when grandly touring in your GT, and the reduced cost would be welcome to anyone. As would the salving of conscience.

The possible problem is that such a Bentley would, surely, lack the effortless pace expected of the marque. Downsizing an engine in the name of efficiency is all very well for the masses, but for a Bentley? Well, let's see.

The familiar Continental has a 6.0 litre, twin-turbo, W12 engine able to produce 567bhp, and is rated at an embarrassing 384g/km CO2. The new car, available as both a GT coupé and GTC convertible, has a 4.0 litre V8, co-developed with Audi, also with twin turbochargers. But adds other cleverness: direct fuel injection and, vitally, the ability to become a V4 when driven gently. The other four cylinders are deactivated by turning off fuel and sparks, and keeping the valves shut.

This V8 produces 500bhp, a figure not far short of the W12's despite the latter's 50 per cent greater capacity. And the V8's CO2 rating is 275g/km – still in the highest tax bracket but in itself an impressive figure for a car so rapid and heavy. It equates to an official average of 24mpg, rather better than the W12 car's 17.1mpg.

The 40 per cent fuel-efficiency improvement isn't just in the official figures. It's achieved in real-world driving, too. Various eco-tricks are used to achieve this, of which the smaller capacity and V4-switch are just two. Other gains come from a new eight-speed automatic gearbox instead of a six-speed, using engine heat to warm the gearbox oil after a cold start, using the alternator to generate electricity only when slowing or braking, better aerodynamics and a small (25kg) weight reduction.

The weight loss and better airflow partly compensate for the small power reduction, so the V8's performance is very close to the W12's. Few would quibble over a 0-62mph time of 4.9 seconds (just 0.3 seconds slower) or a top speed of "over 180mph" compared with 198. Any doubt is erased as soon as you drive this new car, anyway, because it is, quite simply, the most enjoyable road car that Bentley has created in living memory.

How so? The engine accounts for much of it, with a fabulous soundtrack in which a deep bass burble is increasingly overlaid by a staccato crackle as the pace rises. It sounds properly powerful and fast, and feels as keen as it sounds, helped by a swift-shifting gearbox. This is a Bentley as a truly sporting car, a rival for an Aston or Ferrari but with much more effortless verve from low engine speeds than either.

But there is more. Bentley is positioning the V8 as a more sporting car, as signalled by a fiercer-looking front and some small changes to the suspension and steering settings. It still rides beautifully on its computer-controlled air suspension, but there's a new crispness and agility which makes it feel two-thirds the weight of its W12 sibling – and it's a joy to experience.

A much more appealing car which uses much less fuel and costs 10 per cent less. A no-brainer, I believe it's called.