Details on BMW's new N55 engine have been out since last summer, but we haven't discussed them much here beyond telling you that it's the best of the 3 engines (2 for us) that BMW will offer in the 2010 BMW 5 Series GT. But this isn't just a turbocharged inline-6 the company has made specially for misshapen crossovers. Rather, this engine will replace the current twin-turbocharged inline-6 we know as the N54. The N55 shares its all-aluminum block, direct injection system and 10.2:1 compression ration with the N54. And the weight difference between the two is little more than 4 pounds. But the new engine differs in two key ways: --> It has a single, twin-scroll turbocharger (which BMW calls "Twin Power") instead of two smaller turbochargers. --> It is the first BMW inline-6 to use Valvetronic (er, make that the 2nd, as the N52 engine, seen in the 2006 330i, had it first), whereby an electric motor built into the cylinder head continuously varies the amount of valve lift. The addition of Valvetronic reduces fuel consumption by 8 percent. It also quickens response time when you're cruising along at low load and have a sudden, urgent need to be at wide-open throttle. And peak torque (still 300 pound-feet) comes in at just 1,200 rpm now instead of 1,400 with the N54 engine. Peak horsepower is still listed at 300, but the power curve doesn't taper off as soon.