Mercedes-Benz ML55 AMG / Lorinson K43 / RENNTech ML60RS / Stillen GTM 430 S/C M

丽江文子

"Perversion" is such a harsh word, and so relative, isn't it, Marv?

Some would say that strapping superchargers, aero kits, low-profile tires, cut-down springs, and turgid shocks onto sport-utility vehicles -- four-wheel-drive trucks, essentially -- is the height of mechanical kink, the automotive equivalent of dressing up mountain sheep in nylons and stiletto heels.

Others are more broad-minded -- and not just Australians. All's fair in love and tuning, they say, and besides, to develop these vehicles into hot-rodding street machines is only to acknowledge the way they are driven. Who cares if you lose an inch or two of approach angle if you can get through a corner quicker?

If only it were that simple. As we learned, the typical road-racing mods applied to heavy, long-legged, high-centered SUVs can create cascading handling problems, making them devilishly tricky to tune. More on that later.

The concept of a Mercedes-Benz M-class tuner shootout first arose last fall when Brabus, the renowned tuner of the German automaker's products, opened its new office in Newport Beach, California. We had longed to put the company's 582-hp, 7.3-liter, 48-valve M V-12 under our electric eye, as Guinness proclaims it to be the fastest street-legal off-road vehicle in the world.

Alas, Brabus could not supply the title-holding M V-12 or a newer, heavily breathed-on three-valve V-8 (400 hp) M-class. Fortunately, even without Brabus, the field of M-class performance tuners proved to be deep and broad, including Stillen, Lorinser, RENNTech, and of course, AMG, Mercedes' in-house maker of mischief. We extended invitations to each. On the appointed weekend, the four vehicles and their camp followers showed up in southern Arizona for some lust in the dust.

[ 本帖最后由 丽江文子 于 2015-5-21 09:16 编辑 ]

丽江文子

Granted, calling AMG a tuner is a bit of a stretch. ML55s are in every sense factory machines, built on the same line in Alabama as other M-class vehicles.

This shows in the glossy polish of the $65,495 ML55, which has a rattle-free, cast-in-place solidity and refinement that our other test cars lacked. Here the ML55 enjoyed a huge advantage: It was a 2000 model, whereas its tuner brethren were all modified 1999 cars. Consequently, the ML55 sported the dozens of refinements to the M-class -- richer dash materials and better door sealing, for instance -- while the tuner cars had to deal with the somewhat spotty build quality and louche interior of previous models.

Under the ML55's "power domes" on the hood (a heritage note from the 300SL Gullwings) resides an AMG-specific 5.0-liter aluminum block equipped with a forged-steel stroker crank that raises displacement to 5439cc. This three-valve SOHC V-8 is further hotted up with a larger-bore dual-resonance intake manifold, stiffer valve springs, and lightweight modular camshafts. The result is 342 hp at 5500 rpm and a lusty 376 pound-feet of torque at 3000.

"Ah, the wonderful, sensual thrumming of a naturally aspirated V-8!" wrote an editor in the logbook (check his medicine). "Smooth, quiet. Ample reserves of passing power," wrote another. As in all our M-classes, the faucet for this liquid thrust is a five-speed TouchShift automatic transmission. Our test ML55, with 3000-plus miles on it, surged from 0 to 60 mph in 6.5 seconds, 0.3 second quicker than the ML55 we tested last fall. At that rate, this summer these things will be as fast as dragsters.

Underneath, the ML55 wears 285/ 50WR-18 Dunlop SP Sport 9000s on AMG alloy wheels. The ML55 shares its oversize disc brakes (13.6 inches in front, 13.0 inches in back) with the ML430 but clamps them with four-pot calipers. Sport-tuned shocks, lowered front torsion bars, and rear springs are all specific to the ML55 and reduce vehicle height by 0.6 inch, but in general, suspension tuning over the ML430 is mild.

Accordingly, the ML55 offered "factory" ride compliance, supple, with soft, easy body motions over the bumps. "It moves as a suspension should," wrote one editor. "Others say floaty, I say absorbent."

Well, perhaps floaty after all. During our standard emergency-lane-change test, the ML55 heeled over perilously to the right, then heaved left and went broadside through the timing gate, destroying what was left of our poor infrared reflector (the Lorinser had earlier performed a similar feat of derring-don't). Then, as the AMG was curving across the tarmac, it began to rock laterally and hop on its left wheels, pogoing violently until the two inside wheels left the ground altogether. There was a lot of gasping. Scary.

It occurred to us then that these vehicles were so good they had lulled us into a false sense of security. But in the extremity of this violent avoidance maneuver, their true natures came out. Ultimately, these are still tall, short-wheelbase SUVs with long-travel suspensions. And they are quite heavy (the AMG was the heaviest at a girthy 4913 pounds) with high centers of gravity. When you put such vehicles on sticky high-performance tires, you increase the likelihood that they will trip, tip, or tumble during an emergency maneuver. (Note how we delicately leave out any mention of large, antlered ruminants that live in northern latitudes.)

M-class vehicles, of course, come standard with the Electronic Stability Program. If ESP senses an impending loss of control, it will selectively brake one or more of the wheels to reestablish equilibrium, dramatically reducing the chances of a spin or slide.

Unless you turn it off, which we had. Typically, we record higher performance numbers without these overly cautious interventions (ESP was off for each of the vehicles tested). But with the M-class, it seems clear that many major design decisions concerning suspension travel, shock valving, spring rates, and acceptable tires were computed with ESP in mind. To turn it off, Mercedes argues quite reasonably, is to throw off the intricate calculus of the vehicle's suspension.

But if ESP is crucial to the vehicle's safe handling, why is there an "off" switch? Declareth the owner's manual, "To improve the vehicle's traction when driving with snow chains or starting off in deep snow, sand, or gravel, or when off-road driving, switch off ESP." Otherwise, the implication is to leave on the ESP.

We have two suggestions: Strengthen the language of the owner's manual, discouraging owners from turning off the ESP, perhaps including the phrase, "Danger, Will Robinson, danger!" Or make ESP speed-sensitive so that it automatically comes on above a certain speed. Mercedes says it will consider these suggestions.