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The fact that Mercedes-Benz could boast having the world's fastest sport-utility vehicle in the ML55 obviously didn't sit well with BMW. So less than two years after unleashing the X5 4.4i, those wacky Bavarians have hot-rodded the X5's big V8 to take on the ML55 head-to-head. Unlike Mercedes, which aligned its super-SUV with its in-house tuning company, AMG, BMW officials are adamant that their top-of-the-line Sport Activity Vehicle (SAV) won't get an "M" badge. For one thing, the appellation MX5 would probably send Mazda into legal fits. For another, BMW's Motorsports GmbH wants to restrict its moniker to only the sportiest of the company's sedans and coupes, and an SUV (oops, sorry, an SAV) just doesn't qualify.
So the new X5 is called the 4.6is and, according to BMW, its 4.6-liter V8 boasts 347 horsepower at 6,500 rpm and 354 ft-lbs. of torque at 3,700 rpm (compared with 342 horses at 5,500 rpm and 376 ft-lbs. as low as 2,800 rpm for the ML55). Besides the increase in displacement, BMW says the extra ponies are the result of new induction and exhaust systems as well as revised fuel injection mapping.
It may not wear an "M" badge, but the new 4.6is certainly scoots along quite nicely, especially when you row the revised Steptronic five-speed automatic transmission like a manual. There's noticeably more torque than the standard 4.4i, though not quite enough to match the larger-displacement ML55.
However, like most BMW engines, this 4.6 is eager for revs. Compared with the longer-stroke ML55 engine that sports only three valves per cylinder, BMW's four-valve engine is more responsive over 5,000 rpm. BMW claims the 4.6 will accelerate to 60 mph from a standstill in less than 6.5 seconds. In comparison, Mercedes claims a 6.4-second time for the ML55 to reach that speed. So straight-line performance between the two is a wash. BMW, however, says that the X5 4.6is "will exceed 149 mph" while the ML55 tops out at 144 mph.
The obvious question, though, is why BMW didn't save itself the development dollars and just slip the 5.0-liter V8 from the M5 Sedan under the X5's hood. Presto, instant 400-horsepower hooliganmobile. Certainly, as our experience with the 700-horse X5 Le Mans prototype proved (see sidebar), the X5 could more than handle the power. According to Eduard Walek, chief project engineer for the X5, just such a beast does exist (and with the conspiratorial wink he gave, it sounds like it's in his garage). The problem, says Walek, is that the M5's power is concentrated well up the rev scale, which is not conducive to off-roading. Considering that it's doubtful that many X5s will ever see anything muddier than a poorly graded country club parking lot, it's awfully tempting to contemplate an M5-powered X5.
Other than the boost in power, the 4.6is we drove was amazingly stock. Besides the addition of the same humungous Michelin Diamaris 20-inch tires (315/35ZR20 rear and 275/40ZR20 front) as the Le Mans prototype, the 4.6is features the current X5's optional "sport" package as standard equipment. Rear brake calipers come from the M5, while the front disc arrangement is sourced from the 7 Series. Firmer dampers and springs as well as larger sway bars improve turn-in, cornering and stability. Light years ahead of garden-variety sport-utes, the 4.6is feels remarkably composed. There's less body roll through fast corners than the ML55 and understeer is reduced compared with the AMG-tuned Mercedes.
In other regards, the 4.6is we drove was a standard X5, right down to having the same All Season Traction Control (AST) and Hill Descent Control (HDC) systems as the 282-horsepower, 4.4i version. That also means having all the creature comforts one expects of a BMW, albeit with a few color schemes that won't be available in the base versions. Inside, seats similar to those in the "Sport" package beckon, but with a different cloth/leather upholstery. A gauge set similar to the M5's sums up the predominant differences between the 4.6is and the 4.4i.
A few exterior visual cues distinguish the 4.6is from the garden-variety 4.4i. There's more pronounced wheel arches to cover the huge 20-inch wheels, a body-colored front spoiler with side wind-splitters and xenon headlights, which are optional on other X5s, are standard on the 4.6is. A lower rear spoiler and dual oval exhaust outlets complete the package.
Nonetheless, Americans may wish for a more overt indication of how special this new X5 is. German drivers revel in this kind of stealth-mobile, but we North Americans aren't quite as subtle. Maybe some outrageous OZ wheels and some seriously sculpted fender flares are in order. Or how about a neat little "M" badge along the lower door trim and on the rear trunk lid? Oh, and while you're at it, why not throw in that 400-horsepower M5 engine as well? We don't really want to get anything this dynamic muddy.
Driving the X5 LeMans at Germany's Nurburgring
I'm pretty sure I'm supposed to be having a good time. In fact, I'm absolutely positive. Didn't BMW's publicist say, "Come to Germany. Drive one of our X5 sport-utes. Have a wonderful time"? I'm certain he said wonderful. He wouldn't lie, would he?
Why, then, am I praying with an "I'll never drink Tequila again" fervor if the Almighty will just please get me back to the garage in one piece and without losing the lovely breakfast the Dorint Hotel served two hours ago?
It might have something to do with the fact that Hans-Joachim Stuck, of World Supercar and Le Mans fame, is piloting the X5 I'm strapped into. Or maybe it's that the corners he's flinging the Bimmer into belong to the Nurburgring, more than 12 miles filled with 192 of the most diabolical twisties ever paved by man.
Normally, either of those two circumstances would be enough to strike terror into my lily-livered heart. In this case, however, the truly terrifying part of this whole experience is that a few especially demented BMW engineers have stuffed this particular X5's engine bay full of McLaren 6.0-liter V-12 (actually the engine from BMW's own LMR race car, itself the successor to the original V-12 developed for McLaren).
Did I mention that it was raining? Or that the X5 Le Mans was running on street-legal, Michelin Diamaris tires? Those poor Michelins were being asked to transfer a rootin', tootin' 700 horsepower courtesy of an upgraded version of the engine that powered the '99 Le Mans champion. That engine, producing 'only' 580 horsepower, is restricted by twin 32mm throttle bodies rather than the 80mm items on the X5, but still managed to propel the LMR to speeds well in excess of 200 mph down the Mulsanne straight.
BMW claims that those 700 ponies are enough to propel the X5 Le Mans to 60 mph in about 4.5 seconds. Quite quick to be sure, but still a tick slower than a road-going, 415- horsepower Porsche 911 Turbo. Having to motivate well over 4,000 pounds of metal, rubber and plastic has a way of blunting even the most prolific engines.
BMW also claims a top speed of 173 mph, but like the claimed zero-to-60 time, that seems mighty conservative. With Stuck rowing the gears, the Le Mans powered its way to an indicated 169 mph with ridiculous ease. Nonetheless, the X5's bluff body is hardly as aerodynamic as an open-air Le Mans racer or even a street-going Porsche, and both have significantly higher top speeds, despite their relative paucity of horsepower.
Nonetheless, those performance figures don't even begin to describe this X5's amazing performance. The aforementioned Porsche Turbo may win the spec-sheet grand prix, but the way the Le Mans accelerates through the gears makes the twin-turbocharged 911 seem positively anemic. Nothing I've driven compares with the sheer, gut-wrenching acceleration this one-off X5 generates at the merest whiff of throttle.
I was almost thankful for the wet track as some of the Nurburgring's slipperier corners tempered Stuck's enthusiasm, meaning that we were screaming around blind, off-camber corners at merely demented, rather than truly death-defying, speeds. Not that the difference helped my queasy stomach or tempered my desire for an extra set of brake pedals.
Despite the wet, slippery track and the incredible speeds, there wasn't a truly trouser-soiling moment, a testament to the X5's ability to withstand torque that would tie most sports cars up in knots. In fact, according to chief project engineer Eduard Walek, that's the raison d'etre of the Le Mans prototype — to test the limits of the standard X5's chassis and powertrain.
Apart from lowering the chassis by 45mm in the front and 40mm in the rear, shortening and stiffening the springs as well as the dampers and stuffing some truly gargantuan tires (275/40ZR20 fronts, 315/35ZR20 rears) under the truck, the Le Mans prototype is basic X5. Inside there is a Recaro racing seat and a roll cage for the driver, but otherwise the interior is remarkably stock, with all the switchgear and convenience items of the production vehicle.
Even much of the drivetrain is stock, with the transfer case and front differential sourced from a standard X5 4.4. The rear diff is grabbed from the all-conquering M5 for its limited-slip locking feature. The six-speed gearbox, meanwhile, is from the now discontinued 850Ci.
This last caused Walek some concern, so certain was he that the Le Mans X5's monstrous torque would shred the transmission's internals into shards of expensive swarf. In fact, Walek seemed more surprised than anybody that the prototype ran lap after lap without the slightest hiccup, at least from the truck itself (there were a few mewlings from the passengers). Despite the best, or worst, Stuck could throw at it, however, the Le Mans behaved as well as any normal X5, save for the unmuffled V-12 snarl from a custom-made stainless steel exhaust system and the gut-wrenching performance.
The one downside to this grand experiment is that Walek is adamant that BMW will never produce an X5 Le Mans. And unlike other companies that play coy with their concept cars in the hope that public demand will force their hands, I'm certain that this most outrageous SUV (or more accurately SAV, in BMW parlance) is destined for BMW's museum.
It does prove what many had long suspected — that BMW overbuilds its road-going cars. Even horsepower levels comparable to current Formula 1 open-seaters aren't enough to upset their basic road-holding ability. — D. John Booth
