What's a twin-scroll turbo? In a regular turbocharger, exhaust gas from a single header hits the impeller. In a twin-scroll set up, two exhaust headers feed two streams of spent gas into a single impeller 180 degrees apart. This is better because the two streams of gas roughly mimic the inherent smoothness of an inline-six cylinder engine, thereby spinning the impeller in a smoother fashion. This is apparently more efficient. Power, however, is unchanged at 300 horsepower and 300 lb-ft of torque.
Of course, BMW's weird little secret is that the old twin-turbo motor made closer to 330 hp and 330 lb-ft of torque. We have no reason to believe the twin-scroll job is any weaker than the motor it replaces. Check it: 0-60 mph takes place in 6.1 seconds, wowza fast for a six-cylinder SUV. Compare it to the Cadillac SRX Turbo, which features 300 horsepower and 295 lb-ft of torque, yet takes 7.6 seconds to hit 60 mph. Likewise, the BMW dusts off the quarter-mile in an impressive 14.6 seconds at 92.5 mph, while the SRX Turbo takes a still-respectable 15.9 seconds with a trap of 90.7 mph.
The Cadillac obviously weighs more, right? Um, no, not at all. The SRX Turbo flattens the scales with its 4595 pounds. Heavy, of course, but hang on to your sense of outrage-the BMW X5 xDrive35i weighs a lardy 4794 pounds. That's 199 extra pounds for the X5, for those of you that lack the skills to subtract things up right. How on earth is this possible?
Part of the reason why the Bimmer's so much quicker is of course the fibbed output numbers. Put another way, the twin-scroll motor makes whatever car it's in a perennial ringer. We also suspect that the X5's new fast-shifting 8-speed autobox has something to do with such highfalutin numbers. While the ZF-sourced unit isn't a dual-clutch, it's the next best thing.