Sunday, July 26, 2009

First Drive: 2010 BMW X6 M

A screw-up by BMW's German PR department has given me exactly one hour and fifty-eight minutes to write my driving impressions on the X6 M before the embargo lifts. That's not nearly enough time to collect my thoughts and write a coherent story, much less wade through the 25 pages of technical information we were just handed. So you'll have to wait a few days for the full story. But there's no reason you should have to wait for the unfiltered, raw information. Here I go:

The X6 M will cost $89,725; the X5 M (which we didn't drive, but which shares all powertrain components) will be slightly cheaper, at $86,225. Under the hood is an M-massaged version of the 4.4-liter twin-turbo V-8 that made its first appearance in the X6 xDrive50i and also does duty in the 7-series sedan.

Massaged is a loose term. The engine, code S63B44, uses a brilliant-and patented-exhaust manifold and dual twin-scroll turbochargers to reduce turbo lag to levels previously unheard of. Coupled with an automatic transmission, the lag rounds to zero. It's there, of course, but this is probably the least laggy turbocharged gas engine in the world. I expect nothing less from M-a company that has gone through the outrageous expense of installing independent throttle bodies on each cylinder of every normally aspirated engine it developed. (Those multiple throttles shave milliseconds from response time-turbos can sometimes add multiple *seconds* of lag.)

Output is quoted at 555 hp, with a perfectly flat plateau of torque (500 lb-ft) from 1500 rpm to 5650 rpm. The engine revs to 7000, though by that point it's lost quite a bit of its thrust. The transmission is a special version of the brilliant ZF-developed 6HP26 6-speed automatic, which gains an "S" suffix. S obviously stands for "Oh My God," because shift times are reduced to something resembling a dual-clutch gearbox. According to an engineer, shifts in manual mode are accomplished with the torque converter locked, and the entire shift takes place within the time needed for one single, solitary power stroke. The computers simply misfire one cylinder on purpose for an incomprehensively short interruption in torque, and by the time the next cylinder fires (one four-hundreth of a second later if the engine is at 6000 rpm), full power is given back. Shifts in automatic mode are also very quick-though not quite as fast, and are much smoother.

BMW claims that the 5300-plus lb SUV will accelerate to 60 mph in 4.5 seconds, and there's no doubt in my mind that it will. In fact, if my butt is calibrated correctly, you can expect to see numbers even quicker than that from magazines that measure 0-60 mph times without rollout.

Both the X5 M and the X6 M use the amazing rear Dynamic Performance Control differential first seen in the regular X6. The electronically controlled diff can transfer up to 1300 lb-ft of torque from one rear wheel to the other, helping turn the car to follow the driver's desired path. The X6 M put all of its power down without any drama whatsoever. The only time we saw wheelspin was during mid-corner slides after bouncing off curbing at the Road Atlanta racetrack, where we put the X6 M through its paces.

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