E55 AMG: Twist and shout

The engine of the 2004 Mercedes-Benz E55 AMG produces 516 pound-feet of torque between 2,650 and 4,500 rpm. For a lot of people, this sentence means nothing. What, after all, is torque? What is a pound-foot, and is 516 of them a good thing or bad? “Pound-foot” seems like nonsense verse, like early Andre Breton or late Snoop Dogg.

You’ll forgive my being didactic, but the E55 AMG -- the ultra-performance version of Mercedes’ E-Class -- can’t really be appreciated without some grasp of automotive mechanics. Most cars: They go, they stop, they drink gas and poop exhaust fumes. What’s to explain?

The $76,200 E55, on the other hand, is the most potent production sedan on the planet. Among its parlor tricks: 0 to 60 mph in 4.2 seconds, quicker than a Ferrari 360 Modena, Corvette Z06 or Aston Martin Vanquish, according to Road & Track magazine. The E55 also blitzes a quarter-mile in 12.4 seconds, as fast as that purest of sports cars, the Porsche 911 Turbo. And although the AMG’s top speed is electronically limited to 155 mph, the true top speed is, by my calculations, more like 185 mph.

What makes this ordinary-looking, 2-ton luxury grocery getter such a monster is none other than the oft-misunderstood torque, pouring out of the car’s 5.4-liter supercharged engine like the business end of Hoover Dam.

Torque is, simply, twisting force. Grab a doorknob, twist -- voila, torque.

Torque is expressed in pound-feet (or in the metric system, newton-meters, but let’s not go there, OK?). As Archimedes well understood, a lever multiplies force. Imagine you are loosening a rusty bolt. If you use a foot-long wrench and put 100 pounds of pressure on one end, you are applying 100 pound-feet of torque to the bolt.

The E55 engine’s output shaft turns with a maximum force equivalent to 516 pounds of pressure on that same foot-long wrench. It’s really pretty simple.

Horsepower -- that familiar unit of power, reassuring in its equine obviousness -- is anything but. The term was coined by Scottish engineer James Watt, who reasoned that a strong horse could raise 550 pounds 1 foot in one second. Trouble is, his unit of measure is foot-pounds -- the converse of torque’s pound-feet -- and it describes linear, straight-line force, while torque describes rotational force.

These days, horsepower is calculated as a numerical product of measured torque multiplied by engine rpm, divided by 5,252 (a bit of mathematical housekeeping that cancels out minutes and seconds and turns straight-line into rotational force units). In the E55, the engine produces peak horsepower of 469 horsepower at 6,100 rpm, which is about 404 pound-feet of torque.

It all seems so innocent, like chalkboard arithmetic you might remember from high school physics. But for car enthusiasts, these numbers are, well, scary, with the kind of dwarfing immensity one associates with thermonuclear footprints and ICBM throw-weights. Imagine this scenario: You are merging onto the 10, and there’s a break in traffic. Feeling frisky, you mat the throttle ... one-one-thousand, two-one-thousand.... Count to five and you are commuting home at 120 mph or more. How do you look in an orange jumpsuit?

Here’s a little gearhead dish: While peak horsepower has a certain marquee value, it’s not especially relevant outside of top speed. Acceleration -- the sensual, guilty, giddy gestalt of tramping the gas pedal and feeling yourself shoved into the fast-forward scenery -- is the product of engine torque pitted against the mass of a car.

I’ll risk one more physics equation: F = Ma. Fun equals mass times acceleration. The E55 has F in abundance.

AMG -- based in Affalterbach, Germany, not too far from Stuttgart -- is the wholly owned mischief maker for Mercedes-Benz. As a matter of company policy, an AMG-tuned model is the top offering in each of the model lines.

Obscene power is AMG’s calling card, delivered by highly developed engines, each hand-built and signed by the technician who assembled it. The E55 engine starts life as a 5-liter V-8 casting, which is then endowed with longer connecting rods (“stroked” is the term of the art) so that it displaces 5.4 liters. AMG uses high-performance engine internals, including matched pistons, a reinforced crankshaft and lightweight single-overhead cams to actuate the engine’s three valves per cylinder. Ignition spark is provided by twin coils over twin spark plugs.

A vast amount of binary code from the Bosch engine management system minutely adjusts the fuel-injection spray and timing for each cylinder.

All of which would make for a very healthy hot rod, but AMG goes on to add an enormous supercharger to the engine, plumbed with an air-to-water intercooler (the air consumed by the engine is cooled, making it denser and creating more power in combustion).

A supercharger is essentially a compressor -- or, as the Germans spell it, Kompressor. When fully engaged, the supercharger compresses intake air an additional 13.1 pounds per square inch, almost a full bar over atmospheric pressure.

To visualize what this supercharger means to engine power, imagine building a roaring fire in your fireplace. Now imagine pointing a leaf blower at it.

Unlike BMW’s engines, which use the variable-valve timing and lift to optimize the torque over a broad range of rpm, the E55’s engine varies the pressure from the supercharger to accomplish the same mission. The AMG’s peak torque plateaus between 2,650 and 4,500 rpm. This accounts for the car’s seemingly bottomless well of power. It just keeps pulling and pulling. At speeds well above 100 mph, the car still has enough dynamite to blow your license to kingdom come.

This torrent of power is sluiced to an AMG-modified five-speed automatic transmission. You can shift gears by moving the stubby pistol grip shifter east-west, or if you have selected manual mode you can shift with the buttons on the back of the steering wheel. This unit is probably the smartest and quickest of the pseudo-manual transmissions on the market, with none of the blowzy, off-throttle intermissions common with other auto-manuals as they consider their next gear selection.

The car bolts from gear to gear like Lance Armstrong in the Alps. The tranny is also adaptive, meaning it considers driver behavior -- lead foot or pussyfoot -- and modifies its shift points accordingly. The E55 will downshift automatically during braking and refuse to upshift during hard cornering to avoid unsettling the car’s balance.

The E55 uses Mercedes’ Airmatic pneumatic suspension, which automatically adjusts firmness and rebound according to road condition, speed and cornering attitude. The car also offers a sport suspension mode, firming up the corners for a full-on flog-fest, and a four-position ride-height adjustment. The car gradually lowers itself to the tarmac as speeds increase. Steering feel is heavy and accurate as a diamond cutter, and the quick-ratio rack-and-pinion system tacks faultlessly.

The brakes are gigantic vented discs with 8-piston calipers upfront, capable of bringing the E55 to a halt in 118 feet from 60 mph. I wouldn’t be the first to complain about the rather numb feel of the E55’s brakes, which use brake-by-wire technology with an artificial, haptic feedback in place of the gathering resistance one feels with a regular hydraulic system.

The Sensotronic system does have the virtue of exerting precise amounts of brake pressure at each brake rotor depending on brake pedal pressure, car attitude, and slip and grip, as directed by the car’s ABS, traction control and stability systems.

What’s it all mean? Few cars can match the E55’s sheer technological density, most of which is so thoroughly integrated as to be invisible and, perhaps, unappreciated. What you cannot help but appreciate is the exquisite excess of power. Turn off the traction control, load up the torque converter (left foot on the brake and right on the gas), and let her rip. This car can lay down two 10-inch-wide streaks of very expensive rubber for 50 feet. That’s fun.

Once you are done showing off -- and certainly we hope the urge passes quickly -- you are left with a car of stunning athleticism wrapped in a rather unassuming package. The E55 doesn’t look much different from an ordinary E-Class. Little denotes a car that can go wheel to wheel with a Dodge Viper. It is, however, replete with nearly every amenity in the Mercedes catalog, from to Keyless Go starting (it senses the key fob in your pocket) to rain-sensing wipers to elegant ambient cabin lighting.

Given its price tag and performance, the E55 is a grand theft auto.

I am often asked what is the best car in the world (whereas I am not often asked to explain the subtleties of torque versus horsepower, but there you are). Lately, I’m inclined to answer that the E55 AMG is the car. Is it perfect? No. The styling is rather bloodless. The ride is leather-stiff. A little more mechanical grip in the corners would be nice too. But this car is an almost surreal combination of performance and luxury, neither compromised on account of the other.

Torque really does makes the world go round.

Times automotive critic Dan Neil can be reached at


2004 Mercedes-Benz E55 AMG

Wheelbase: 112.4 inches

Length: 190.3 inches

Curb weight: 3,990 pounds

Powertrain: Supercharged 5.4-liter, 24-valve V-8; five-speed automatic with Touchshift manual shifting

Horsepower: 469 hp at 6,100 rpm

Torque: 516 pound-feet at 2,650 to 4,500 rpm

Acceleration: 0 to 60 mph in 4.2 seconds

EPA rating: 14 miles per gallon city, 21 mpg highway

Price, base: $76,200, including $720 delivery

Price, as tested: $76,200

Competitor: Audi S6, BMW M5

Final thoughts: Snooper Dooper

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