The Economist:

FOR years, the motor industry lived by the mantra, “bigger is better”. The number of litres that a car’s pistons displaced within its engine’s cylinders was a matter of pride for its owner. This was because displacement equalled power, and power equalled—well, whatever it was that the owner wanted to show off beyond the mere ability to travel from A to B. Times change, though, and technology moves on. Power is no less in demand than it was, but as the clamour for fuel economy rises, raw displacement, which sucks fuel from a tank like an enthusiastic child with a straw and a bottle of pop, is going out of fashion. Instead, a new mantra is taking over. This is, “small is beautiful”.
 What tickles today’s petrolheads, therefore, is not so much how many litres an engine displaces as how much horsepower it can extract from a given volume. For, even as they get more powerful, car motors are shrinking. The smallest member of Ford’s EcoBoost range—a one-litre, three-cylinder device—delivers more power than a 1.6-litre, four-cylinder engine of the previous generation. It is now fitted to one in five of all Ford cars sold in Europe.