Now BMW has revealed the next stage of its efficiency push with a three-cylinder, 1.5-litre engine family. They will power the next-generation Mini Cooper, as well as smaller BMW models such as the 1 and 2 Series, and possibly the 3 Series.
The petrols will produce between 122hp and 224hp and 133 and 177lb ft of torque. The diesels will be offered in various states of tune between 82hp and 184hp. Diesel torque figures range from 166-243lb ft which, from a 1500cc engine with three cylinders, sounds pretty impressive. Expect suitably astounding economy and C02 figures when they emerge.
BMW claims that every derivative of the new 1.5-litre three-pot shares 60% of its components and 40% of its structure, regardless of fuel, massively reducing costs.
It has also introduced a range of technologies to boost efficiency and refinement. These include variable load control, direct injection and, on the petrol versions, Valvetronic variable valve control. BMW has also fitted a torsional vibration damper to reduce the innate vibrations of a three-cylinder engine. It is also promising an "extremely vivacious and sporty" exhaust note.
So, with BMW making the transition to smaller, turbocharged units, is the game up for naturally-aspirated engines? Ford would seem to think so, with the groundbreaking 999cc turbocharged EcoBoost engine set to appear in the next Mondeo. But then manufacturers like Mazda are pursuing more efficient production methods to allow for non forced-induction engines to feature in cars like the upcoming 6. Weight reduction could will also play a key role; you only have to look at the efficiency achieved by Lotus models with fairly low-tech atmospheric powerplants to demonstrate the possibilities of 'adding lightness'.