Small is the new big where engines are concerned. Just ask BMW – it's become the latest in a growing number of manufacturers to create super-small engines that power relatively large cars. Its offering, a 3-cylinder 1.5-litre TwinPower unit, is set to feature in its entry-level 1-Series and Mini cars from 2013 and beyond.
BMW's 1.5-litre TwinPower engine is the company's first to feature just three cylinders. In effect a 6-cylinder unit chopped in half, it drinks less fuel and emits far fewer emissions than its four and six-cylinder counterparts – between five and 15 percent less depending on how aggressively it's tuned.
This engine's major drawback given its small displacement and dearth of cylinders should be a crippling lack of power. However BMW has worked its magic to ensure it's no runt. With the help of twin scroll turbocharging, the engine is capable of producing between 30kW (40bhp) and 50kW (67bhp) per cylinder, meaning it has the potential to produce in excess of 200hp if BMW so chooses. 270bhp is certainly plausible, though the responsiveness and reliability of the engine at such power levels would become a concern.
We got the chance to try a BMW 1-Series equipped with a unit cranked up to 180hp and it was a truly joyous thing. Contrary to what you might expect from a lump of this size, the engine sounded like it was many times larger – a deep, raspy, loud, boisterous-sounding din erupts from the thing after even the most gentle caress of the throttle. It pulls away smoothly, urging the car forward on an almost seamless surge of power, aided by BMW's 8-speed automatic transmission (it'll happily work with manual boxes, too, we're told).
BMW didn't quote a 0-60mph time, but between 7 seconds shouldn't be too wide of the mark. Nail the thing and it'll throw you back into your seat as it springs toward the horizon. The fully automatic transmission mode grants a linear surge of power, but semi-auto is where it's at. Each flick of the upshift paddle behind the steering wheel interrupts the raucous engine note with a joyous bark-cum-cough, an almost celebratory grunt of pleasure that begs you to keep your foot planted and repeat the experience. Second, B-b-b-boom! Third, B-b-b-boom! Fourth! Yes!
It's a party trick caused by deliberately shutting down one of the cylinders, dumping its fuel load and igniting it into the exhaust system in a flamboyant, 'brap'. Its pure showmanship on the part of the engineers, and it's unlikely to be carried over to production versions of the engine, which is a real shame.
BMW is unlikely to offer the 1.5-litre engine in a more sedate state of tune, with a quieter exhaust and less aggressive upshifts. This makes sense, we suppose – you'll be able to park the 1-Series outside your house without shattering windows and fuel economy and emissions will be worth writing about.
The 1.5-litre engine has a bright future. It'll appear as an option on entry-level BMW 1-Series and Mini models, and will even work alongside a pair of electric motors to power BMW's i8 plug-in hybrid. It could even pop up in a high-performance M car, such is its breadth of ability.
Don't confuse its size with a lack of ability. Larger engines may have garnered the lion's share of plaudits over the years, but this lump, along with similar models that crop up in the Focus Ecoboost, for example, suggest tomorrow will be ruled by the underdog.