The SMG's launch control holds the big 5.0-liter V10 at an uneven 4,000 rpm, its warbling high-speed idle signaling that all 10 cylinders are champing at the bit. Let go of the SMG's gearshift lever while simultaneously keeping the throttle pinned and the tires squeal, as the big V10 spins to its 8,250-rpm redline faster than my 1.33 gigahertz laptop can type the words. Flick the steering wheel-mounted upshift paddle for second and the 285/35ZR19 rear tires chirp under the strain of all that torque. Split-seconds later, you're doing the same thing for third and the tires still can't hold traction, squealing once again as the V10 starts to sing its post-6,000-rpm, Formula One wail. A mile later you back off, the speedo hovering around 160 miles an hour. At those speeds, the pylons demarcating the course meld into one long orange blur and the 1,000-foot braking area that BMW has provided to get the M5's 3,869 pounds back down to a decent speed seems impossibly short. Cripes, this thing is fast. And you haven't even hit the button: The one that makes the M5 feel as if it's grown a turbocharger ? the button that kicks you so hard in the pants that it makes that last top-speed run seem like a Sunday hop to your favorite bar for wine-soaked steaks and a side of couscous. The button is the power switch just forward of the gearshift lever. When the V10 is first fired up, it defaults to its 400-horsepower mode, a figure not coincidentally identical to the maximum output of the outgoing M5's 5.0L V8. And since the two cars weigh virtually the same, it means the new V10 M5 in its economy mode is as quick as the old V8 was at full speed. Light up that power button and it feels as if the BMW has indeed grown two extra cylinders, though, in fact, what it does is let the M5's 10 individual throttle butterflies completely open (the reduced power mode restricts them to about 90 percent). That mile-long straight where the M5 previously just managed to top out at 161 mph? Well, in full 507-hp mode, it tops 167 mph with almost a half a mile to spare before that aforementioned braking zone. BMW claims a 0-to-62-mph time of 4.7 seconds, which is about identical to a Subaru WRX STi. Methinks the German automaker is being a trifle disingenuous because the Subaru ? as rapid as it is ? would need a bottle of nitrous and a tornado-force tailwind to keep pace. But then what do you expect from an engine that's cast in the same facility as the BMW-Williams F1 motor and is the largest naturally aspirated engine I can think of that exceeds that Holy Grail of more than 100 hp per liter of displacement? Especially one that has 10 individually tuned inlet manifolds, BMW's BI-VANOS system with variable valve timing on both intake and exhaust cams and sounds just like a F1 engine once the revs climb past 6,000 rpm. As a last point of reference, it's also worth noting that at 7.7 pounds per horsepower, the M5 is the most powerful BMW sold anywhere in the world, eclipsing even the limited-production, carbon-fiber-infused M3 CSL. Of course, the magic of BMW M cars has always been their massive performance accompanied by incredible civility. Out and about, the M5 could be a garden-variety 5 Series were it not for the herky-jerkiness of the SMG tranny. Much improved over the previous such transmission used in the M3 ? and newly fortified with seven forward gears ? its shifts are fairly smooth until maximum warp is demanded. Then gear changes happen with all the subtlety of Jeff Gordon charging to the front of the Daytona 500. In the SMG's automatic mode, shifts also feel more sophisticated than in previous versions. There's not as much gap between upshifts and less hunting for gears. Nonetheless, you can fool its computer occasionally, and a foot full of throttle is greeted by a delay while the M5 searches for the appropriate gear. It matters not a whit, of course, when you're going for it. Being able to get instantaneous gear changes with the flick of a paddle is worth the trade-off. And so is, of course, the SMG's launch mode. For those occasions when you just have to blow off that Camaro from a stoplight, the launch mode automatically sets the M5 for optimum drag-stripping. Similar to the system used in BMW's F1 racers, you first have to disable BMW's DSC (dynamic stability control) and select the sportiest of its manual-shifting modes. Then you hold the gearshift lever forward and mat the gas pedal. The car remains stationary with the engine revving at around 4,000 rpm until you release the gear lever. Then all hell breaks loose as 384 pound-feet of torque and 507 hp are transferred to the tarmac by the SMG's computer-controlled manual clutch. It makes for rapid getaways. BMW even claims that the sophisticated SMG system has a fail-safe limiter which senses when you've abused the clutch too much and shuts down the whole system. The M5's brakes don't seem to need any such special treatment, though surprisingly the front calipers only have two pistons rather than the de-rigueur-for-a-sports-car four. But the front discs measure a massive 14.7 inches in diameter and provide more than enough leverage to speedily get the Ăźber-sedan down from its top speed. If the engine is a leap forward, the M5's chassis is more evolutionary. The basic setup and dimensions remain true to the 5 Series with identical measurements for the front and rear track and wheelbase. The M5 adds an Electronic Damper Control that lets the driver choose between three suspension settings ? comfort, normal and sport. Surprisingly, for a car of its massive abilities, the comfort mode is actually quite compliant, the suspension swallowing all but the harshest bumps. And in sport, there's precious little body roll and excellent turn-in. That said, despite the claimed fifty-fifty weight distribution, the M5 will understeer ? especially when pushed through low-speed corners. Mind you, that's at lateral G-force levels that would challenge a Corvette. And oversteer, of course, is but a quick stab of the throttle and the V10's 507 tire-shredding stallions away. The M5 is equipped with a Motorsport Mobility System that can seal punctures up to six millimeters in diameter. But, the company says, there are no plans to offer run-flat tires as none of the current products can meet its stringent criteria for both ride and handling. Inside, apart from the SMG gearshift and the attendant performance-oriented switchgear, the major differences from a run-of-the-mill, top-line 545 are a beautiful suedelike headliner trim and a head-up display that includes a tachometer. There's also some new electronic trickery like the oil level measurement that can be displayed on the LCD screen between the gauges. The same output also informs the driver about necessary scheduled maintenance. And through the iDrive system, you can configure something called MDrive that sets things like the stability control system and damping system to your personal tastes. Unfortunately, the electronic gadget that promises the most, head-up display's tach, disappoints. It lags behind the real deal by as much as 1,500 rpm and so doesn't prove very useful. Rely on it while driving hard and you will be constantly bouncing off the rev limiter. Which, in the end, is probably the right way to drive the M5 (though your local sheriff might disagree). A regular 545 is a fine-handling, powerful beast with a sweetheart of a motor. But this new V10 is another virtuoso effort from BMW, where superiority is expected. Only this one exceeds even the incredible demands placed upon the M division's broad shoulders.
