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The fact that Mercedes-Benz could boast having the world's fastest sport-utility automobile 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, that aligned it's super-SUV with it's 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 it's moniker to only the sportiest of the company's sedans also coupes, also an SUV [oops, sorry, an SAV] just doesn't qualify.
So the modern X5 is called the 4.6is and, according to BMW, it's 4.6-liter V8 boasts 347 horsepower at 6,500 rpm also 354 ft-lbs. of torque at 3,700 rpm [compared with 342 horses at 5,500 rpm also 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 modern induction also exhaust systems as well as revised oil injection mapping.
It may not wear an "M" badge, but the modern 4.6is certainly scoots along quite nicely, especially when you row the revised Steptronic five-speed automatic transmission like a manual. There's noticeably additional torque than the basic 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 autos that sports only three valves per cylinder, BMW's four-valve autos is additional 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 was
h. 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 also 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 additional than handle the power. According to Eduard Walek, chief project engineer for the X5, just such a beast does exist [and with th
e 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, that 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 also 275/40ZR20 front] as the Le Mans prototype, the 4.6is features the current X5's optional "sport" package as basic equipment. Rear brake calipers come from the M5, while the front disc arrangement is sourced from the 7 Series. Firmer dampers also springs as well as lar
ger sway bars improve turn-in, cornering also 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 also understeer is reduced compared with the AMG-tuned Mercedes.
In different regards, the 4.6is we drove was a basic X5, right down to having the same All Season Traction Control [AST] also Hill Descent Control [HDC] systems as the 282-horsepower, 4.4i version. That too means having every 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/leathe
r upholstery. A gauge set similar to the M5's sums up the predominant differences between the 4.6is also the 4.4i.
A few exterior visual cues distinguish the 4.6is from the garden-variety 4.4i. There's additional pronounced tire arches to cover the huge 20-inch wheels, a body-colored front spoiler with side wind-splitters also xenon headlights, that are optional on different X5s, are basic on the 4.6is. A lower rear spoiler also dual oval exhaust outlets complete the package.
Nonetheless, Americans may wish for a additional overt indication of how special this modern 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 also some seriously sculpted fender flares are in order. Or how about a neat little "M" badge along the lower door trim also on the rear trunk lid? Oh, also while you're at it, why not throw in that 400-horsepow
er M5 autos as well? We don't really want to get anything this dynamic muddy.
