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by Phil Berg
Competition from Mercedes suggested that BMW wouldn’t let its two-year-old V-8 X5 4.4i sport-utility remain an only child very long before a hot-rod model joined it. On sale this winter is a 340-horsepower hot-rod version called X5 4.6is that boasts the launch capability of a sport sedan: 0 to 60 mph in a claimed 6.2 seconds. Volume will be limited for this hot-rod model, not by production constraints, but rather by a price tag of $66,845, nearly $17,000 more than the 4.4i, and about the same as Mercedes’ ML55 AMG sport-utility.
After a rousing drive, we think BMW is correct in predicting the X5 4.6is will be worth it only to a small group of buyers with specific needs. BMW says those needs include a high driving position and ease of loading stuff into the tall body. Both Mercedes and BMW continue to develop their SUVs for pavement and dirt, though Mercedes maintains its M-Class is capable off-road, while BMW says dirt roads are as rough as they expect an X5's environment to get.
In addition to a beefed-up new V-8, the X5 4.6is' transmission and suspension have been thoroughly revised for less compromised sporty pavement driving. Almost the entire options list except for the navigation system has been loaded onto the 4.6is, too. Inflatable head protection is added to the rear side airbags, and a big navigation screen on a swing-out panel like you'll find on some Mercedes models clears more room on the already large instrument panel. Add fender flares and paint that’s otherwise exclusive to the M sport sedans and roadsters in BMW’s lineup, and you can see what most of the high price is paying for.
The 4.6-liter engine is a bored and stroked version of the muscular 4.4-liter DOHC 32-valve V-8, with compression boosted from 10.2:1 to 10.5:1, and it retains the VANOS variable valve timing system and Motronic engine control. The redline goes up from 6200 to 7000 rpm, and the horsepower peak comes higher, at 5700 rpm versus 5400 rpm. Peak torque goes up 26 lb-ft to 350, but it comes higher up the tach, too, from 3600 rpm to 3700. The tach, and the rest of the gauges, match those of the M5, with small LED indicators that lower the redline until the engine is thoroughly warmed up. The tweaked engine requires a break-in period of 6000 miles before it reaches optimal potential, BMW says.