Engine downsizing is now an established trend in the motor industry. Look under the bonnet of a Jaguar XF or a Mercedes CLS and it's quite likely that you will find a 2.2-litre diesel instead of the big six or eight cylinder petrol engine that you'd previously have expected.
The Volkswagen group has produced some notable 'big car small engine' combinations too, including the Skoda Superb and Volkswagen Sharan, which are available with turbo charged 1.4-litre petrol power units. The reason is that a boosted small engine can provide the power of a big engine while retaining the economy of a small one if, and it's a big if, the whole thing is executed properly.
Now Ford has produced what is probably the most extreme example of engine downsizing so far by launching a version of its Golf-sized Focus with a tiny 1.0-litre petrol engine. Not only is the new engine smaller than anything that's ever been fitted to a Focus before, it's only got three cylinders. Three-cylinder engines are already fairly common on today's smallest models such as the Volkswagen Up but nobody has fitted a three to a mainstream production car the size of the Focus in living memory. One reason that may be controversial is that the number of cylinders an engine has also influences its character; a three cylinder engine tends to have a slightly raggedy note that can give a small car a bit of character but risks being out of place in something bigger and more posh like the Focus.
Of course, just sticking a small engine in a big car isn't going to produce very good results by itself so Ford has incorporated a vast array of performance and efficiency enhancing measures into its new power unit, although it is also quite notable for a feature that has been omitted; most three-cylinder engines are fitted with balancer shafts that make them run more smoothly but Ford has saved weight and friction by dispensing with balancer shafts and instead uses an unbalanced flywheel and specially developed engine mounts in order to smooth things out. Turbo charging, direct injection and variable valve timing allow Ford to extract very high outputs from the new engine, which will be offered in 100 and 125 horsepower versions. These achieve combined cycle fuel consumption figures of 58.8 and 56.5 mpg respectively, and CO2 emissions of 109 and 114 g/km, figures that match some of the best diesels. The engine only weighs 95kg and is so small it can stand on an A4-sized sheet of paper. That in turn means that any car to which it is fitted – and its use won't be confined to the Focus – will be lighter and should handle more sweetly with less weight at the front end.
But the data can only tell us so much about what an engine is really like. The only true test for something as unusual as the 1.0 EcoBoost engine is to take it out on the road – and here the new Focus is outstanding. It pulls smoothly and cleanly, and broadly lives up to Ford's claims that it combines the torque of a diesel with the free-revving character of a good petrol engine. Noise is extremely well suppressed, and on occasions when the characteristic three-cylinder engine note does make itself felt, it has a softer quality than it does with most other threes. At times, it even sounds like a small six, which suddenly makes the persistent suggestions that BMW will do a three-cylinder 3-Series a lot more plausible.
It's just as well that the 1.0 EcoBoost is so good – Ford has sunk so much effort into the thing that it can't afford to offer it only in small volume economy specials. It will be a mainstream engine option, with 100 and 125 horsepower versions between them expected to account for some 30% of Focus sales. The new engine is certainly up to the job and in the current Focus, an excellent all-rounder, it has found a good home. The only remaining question is whether mainstream car-buyers, who are used to using engine size as a guide to performance, can be persuaded. A short test drive should be enough to convince even the most hardened cynic.