Ford Focus 1.0 EcoBoost

How Ford has cut its Focus's CO2 output without compromising power

Overall, it's the best all-round Focus in the current range

Downsizing. It's the word on every car engineer's lips, because smaller is lighter and more efficient. New cars are finally starting to shrink a little compared with their grotesquely bloated predecessors, but with the engines that power them, the process is considerably more advanced.

The idea is that a small engine, boosted by forced induction usually in the form of a turbocharger, can produce the power of a bigger one while using less fuel, weighing less and occupying less space. And it's not just a vague notion of cutting running costs: car-makers' minds are being focused keenly on the reduction of carbon-dioxide output because, from 2015, they will be legislatively assessed on the CO2 output of the cars they sell. If it turns out that the average CO2 rating of all cars sold over a specific period is more than 130g/km, the manufacturers will be fined €95 per excess gram for every car that takes it over that limit. That could be a huge financial penalty.

Now, please meet the most significant piece of downsizing yet. Ford's Focus is a middle-sized family hatchback, and its middle-range petrol engine is a non-turbo unit of 1.6 litres. Or was; that staple engine configuration is now history, and in its place comes a three-cylinder, turbocharged motor of just 999cc. We've seen such tiny engines in so-called superminis, but in a Focus-sized car it's entirely new, and Ford accepts that the public will need some educating.

This mini engine produces the same 125bhp of the old 1.6, a lot more low-speed pulling power and dramatically improved fuel economy. Its CO2 rating in the Focus is 114g/km, it weighs 30kg less than the 1.6, and its cylinder block is so small it can sit on a sheet of A4 paper. This, then, is the new state-of-the-art mainstream motor-car engine. It has direct fuel injection, variable timing for both inlet and exhaust camshafts, and the tiny turbocharger can spin at up to an incredible 248,000rpm.

The exhaust manifold is water-cooled, the cambelt runs in oil so it's silent and everlasting, and unlike most three-cylinders, it has no balancer shaft to damp out the usual vibrations. Instead, it has eccentric weights on the flywheel and front pulley, and the engine mountings let it oscillate laterally, with no vibration transmitted to the car's structure.

Does it work? It most certainly does. The sound it makes is the deep, smooth, sonorous hum typical of three cylinders, but there's remarkably little of it. The tiny turbo spins up to speed so quickly that there's hardly any detectable delay in response, and an almost diesel-like thrust at low engine speeds means the engine easily copes with the long-legged sixth gear. It feels much punchier than the old 1.6, helped by an "overboost" feature, which allows the engine to generate up to 148lb ft of torque for 30 seconds before reverting to the normal peak of 125lb ft.

One side effect of the engine's very low internal friction is the gentle way it slows down when you take your foot off the accelerator. You soon get used to this, and enjoy the extra agility.

This three-cylinder engine is set to become a Ford staple. Experiments with an electric supercharger have shown it able to produce 180bhp without going bang, which raises lots of interesting possibilities for future fast Fords.

Not only is the 1.0-litre EcoBoost Focus the most economical of all petrol-fuelled Focuses, it is also one of the best to drive. Overall, it's the best all-round Focus in the current range, and it should make you feel very optimistic about the future of mainstream motor cars.

Price: From £17,945 (125bhp)

Engine: 999cc, three cylinders, 12 valves, turbo, 125bhp

Transmission: Six-speed gearbox, front-wheel drive

Performance: 120mph, 0-62 in 11.3sec, 56.5mpg, CO2 114g/km