BMW is famous for six-cylinder engines. Half a dozen pistons all in a row is just as much a hallmark as the double-kidney grille or the blue-and-white propeller badge. It’s kind of surprising, then, that the company’s latest adventure in internal combustion is a four-cylinder motor.
Called the TwinPower Turbo 4, it propels the 2012 BMW Z4 sDrive28i when the roadster goes on sale in the fall. The name offers a partial explanation regarding how a two-liter engine can achieve the kind of muscle usually found in something bigger. A turbocharger helps develop 240 horsepower and 260 pound-feet of torque.
Turbocharging has been around for a long time, but it is enjoying a new bout of popularity as the relevant technology keeps improving, such as engine control units and boost controllers. And this version has a twin-scroll setup, which really means the elimination of the dreaded old turbo lag, where pressing the accelerator resulted in a short pause, then a hang-on-for-dear-life dash toward the horizon. It’s all far more civilized these days.
And also more efficient. Thanks to things like ultra-precise computer-controlled fuel injection and variable valve timing, this new engine will be using less gas than a six-cylinder example, and therefore making fewer emissions. During BMW’s announcement at the 2011 New York auto show, no economy or performance figures were available. These will be released, along with the price, later this year.
BMW would only say that it expects “a fuel efficiency gain of approximately 20 percent, combined with the eight-speed automatic transmission” over the current naturally aspirated three-liter straight six in the 2011 Z4 sDrive30i (MSRP: $46,500), which returns 18 mpg in the city and 28 mpg on the highway.
It doesn’t take much of an intellectual leap to work out that turbocharged quartets will make their way under other BMW hoods in the months and years to come. But fear not, anyone with memories of the less-than-thrilling (non-turbo) engine in the 1.9-liter Z3, the Z4’s forebear. This was the last four-potter of BMW’s to be sold in the United States; discontinued in 1999 after a short, unremarkable career. Since then, the company has produced much better versions for some of its European models, which even seem to have a similar smoothness to its six-cylinder counterparts. And this one has a turbo, which is always good for a giggle or two.
COLIN RYAN has driven hundreds of cars thousands of miles while writing for BBC Top Gear magazine, Popular Mechanics, the Los Angeles Times, European Car, Import Tuner and many other publications, websites, TV shows, etc.