Gentlemen, show us your engines.
This inquiry concerns the means by which engineers from four nations put massive horsepower under the right feet of a small number of lucky drivers, where it waits, begs to be used; the means, in short, by which enough torque is produced to pin heads against headrests when a car’s in fifth gear.
The most powerful production cars in the world are built to be exactly that, without apology to anyone who doesn’t want to drop up to a quarter-million dollars or burn through a small oil-exporting country’s daily output on a run up to Big Sur. There is no excuse for these cars, except one: the fascination of engineering huge power from a 125-year-old invention, the internal combustion engine.
In basic terms, the powerplants that drive the Dodge Viper, Bentley Arnage T, Porsche 911 GT2, and Lamborghini Murcilago-the four cars, available in America, that carry the power flag for their respective nations-work just like the four-banger in an old Corolla, or the one in a 20-horse Model T, for that matter: suck, squish, bang, blow. A piston slides down a cylinder, drawing in air and fuel, suck. It moves back up, compressing the mixture, squish. A spark ignites the volatile brew, bang. The piston forces exhaust from the cylinder, blow. A connecting rod and crank convert the back-and-forth action into circular movement at the wheels, and the cycle starts again.
Mind you, we’re talking about three times the power of the typical “sporty” car engine. The Italians and Germans may protest, and the British look askance, but there’s no One True Way to achieve this kind of muscle. The approach each design team has taken is as distinctive as the country its members hail from. Power is a universal language, but in each case here it comes with a heavy accent.
Next: Dodge Viper
DODGE VIPER: PURE CUBIC INCHES
As a throwback to the muscle cars of the 1960s, the Dodge Viper doesn’t turn many tricks to achieve the coveted double five-hundred: 500 horsepower and 500 lb.-ft. of torque. It’s all about size. And that’s as it should be-in America, size matters.
“There was quite a debate as to which engine to put in the Viper,” recalls John Fernandez, director of performance vehicle operations at DaimlerChrysler. Reviving the old 7.0-liter Hemi V8 was considered, but basing the powerplant on the modern Dodge 8.0-liter V10 truck engine won out because “it was pure cubic inches.” “We stayed away from things like turbochargers and superchargers,” says Fernandez, “strictly because of the nature of the car.”
The truck engine block was changed from iron-just too heavy for a sports car-to aluminum, but otherwise the basic layout was unaltered: an overhead-valve V10 with two enormous valves per cylinder. For the 2003 model, as part of a major redesign, engine displacement was increased to 8.3 liters (reaching another 500 benchmark: 505 cubic inches). Big pistons move in 4.03-inch-wide cylinders, reaching peak power at 5,600 rpm. They also have a stroke (the distance they travel up and down in each cylinder) of almost 4 inches. By contrast, the Ford Taurus’s six cylinders have a bore of 3.5 inches and a stroke of 3.1 inches.
“An engine is a big air pump,” notes Fernandez. “We wanted to get the maximum amount of air in and the maximum out. The more efficiently you do that, the more horsepower you make.” Modern-day constraints such as fuel economy and emissions limits complicate the task, but Fernandez claims the Viper, for which EPA mileage figures have not yet been released, gets 22 to 23 mpg while cruising at 70 to 80 mph, and meets all emissions requirements.
Fitting the monstrous engine under the Viper’s low hood was no easy task, so the design for the intake manifold-the pipes leading to the intake valves-was perfected on computer to maximize airflow to the engine. The biggest challenge: managing what Fernandez calls negative horsepower, which occurs when the cylinders don’t fill homogeneously. When that happens, the engine falls prey to different burns and different combustion pressures, with one cylinder working against another.
Bigger engines also mean bigger, and heavier, parts. To ensure high engine revolutions per minute (rpm)-Barry Bonds not only swings a big bat, he swings it fast -special attention was paid to the valvetrain, the engine components that regulate fluid flow in and out of the cylinders. The focus here was not so much on exotic materials but on the painstaking modeling of parts, shaving bits of excess metal to reduce weight. Less inertia means higher engine speeds, and higher engine speeds mean more horsepower.
The approach yields an in-your-face purple mountain majesty of power: simple in concept, outstanding in application. Yet, compared with the other cars on these pages, a comparative bargain at about $75,000.
* Weight divided by torque; the lower the number, the more power per pound
Next: Bentley Arnage T
BENTLEY ARNAGE T: THE MINISTRY OF TORQUE
Now for the royal treatment. The engine in the all-new Bentley Arnage T is puny compared with the Viper’s, but it makes power in even bigger clumps. The 6.75-liter V8 turns slowly, at a maximum of 5,000 rpm, but two turbochargers squeeze the most from every stroke and deliver it in the cool manner of a British butler. The result: 450 hp and 646 lb.-ft. of Gibraltar-moving torque-for a car that, at 5,700 pounds, weighs as much as two Volkswagen Jettas, and, at around $240,000, costs as much as 12.
“Bentley has always been about overwhelming torque and performance,” says engineering chief Brian Gush, adding that the T’s engine is Bentley’s first twin-turbo. It makes the 2002 Arnage T the world’s fastest four-door sedan, electronically limited to 168 mph.
Whereas a conventional engine serves air and fuel to its cylinders via atmospheric pressure, turbocharging is all about force-feeding. The engine’s exhaust gases spin a turbine and a connected impeller that, in turn, packs more air-fuel mixture into each cylinder. This translates to a more powerful push when the mix is detonated.
The added power is nice, but Bentley moved to twin turbos for this drawing-room-on-wheels mainly to reduce emissions. “To feed the large single turbo from both banks of a V8,” Gush explains, “(the exhaust from) one bank had to cross over to the turbocharger.” This cooled the exhaust gases before they reached the catalytic converter (the part of the engine that scrubs exhaust pollutants with the vigor that your manservant demonstrates with his steel wool on the roasting pans at the country house). With two turbochargers, one near each bank of cylinders, exhaust gases don’t travel as far. They reach the catalytic converter hotter, and the converter reaches operating temperature sooner; ergo, startup emissions are reduced.
The two smaller turbos spool up quicker than the single one, reducing the familiar lag time before turbo power kicks in. Along with improvements in exhaust handling, this means more air and fuel are packed into the cylinders, so engineers had to strengthen the pistons. They also changed the valve configuration and ports to improve gas flow.
Chemistry 101 teaches that compressing a fluid makes it hotter. If it’s hot before ignition, the incoming air-fuel mixture is less dense and can expand less, so it creates less power. Thus Bentley removes some of the heat from the air-fuel mixture with an intercooler before it reaches the cylinders. Water flows through two radiators mounted below the front bumper, each with its own fan. Once cool, the water is sent via a closed loop through the intercooler, where it draws heat away from the intake air. The system is separate from the one responsible for engine cooling.
The result is a ride as unflappable as Jeeves, concealing all the hard work that’s happening behind the scenes.
Next: Porsche 911 GT2
PORSCHE 911 GT2: POWER IN A TIGHT SPOT
Porsche’s 911 GT2 is manifestly the product of Weissach engineering wizards in white lab coats and wire-framed glasses. It weighs half that of the Arnage T, and its 3.6-liter engine-though the largest Porsche has ever put in a 911-is significantly smaller. Yet it packs more horsepower.
The GT2, introduced last year, is the quintessential featherweight with a crushing punch. “We believe that lighter is better,” declares Porsche engineer Walter Lewis. Better not only for acceleration, but also for braking and cornering. Engineers even stripped it of the all-wheel drive system found on its sibling, the 911 Turbo.
Though the most modern Porsche yet, the GT2 shares its layout with the original 911, which was essentially a hot-rod Volkswagen Beetle-of-the-gods, complete with engine cantilevered behind the rear axle. (The gods are paying $180,000 for the latest version.) This fact alone limits the engine’s size and weight. Also, in such a small car, too much mass at one end would complicate handling.
The result is an engine that delivers 1 hp for every 7 pounds of car. Such prodigious push comes partly from a maximum engine speed of 6,750 rpm, considerably faster than either the Viper or Arnage T. The 456-hp engine also has four valves per cylinder. These smaller valves are lighter than, say, those in the Viper, allowing higher engine speeds without “float” (in which the valvetrain cannot keep up with the camshaft). The smaller doors can open and close faster than the Viper’s gates, and their larger number ensures the engine moves enough air and fuel.
Like the Bentley, the GT2 has twin turbochargers to force more work from each cylinder. The six-cylinder horizontally opposed engine (think of a V6 squashed flat) has twin intercoolers, though with space-saving air-to-air cooling, which doesn’t require an elaborate system like that on the Arnage T. Special ducts on the GT2’s flanks direct air to the coolers. What the GT2 avoids, however, is the frantic slap-in-the-back power delivery of earlier high-boost turbo motors, thanks to an engineering tidbit called VarioCam Plus.
VarioCam rotates the intake camshafts to precisely tune airflow timing. The cam opens intake valves later at low speeds and at idle, reducing overlap-the time when both the intake and exhaust valves are open-so less intake gases escape out the exhaust valve without being burned. At higher engine speeds, intake valves open earlier. This increases overlap. Engine speed and gas flow inertia prevent intake gases from exiting unburned. There are any number of cam settings between normal and advanced; the engine computer picks the most efficient based on input from onboard sensors and the driver’s right foot.
VarioCam Plus gives the GT2’s engine a surprisingly broad torque curve, plateauing at 457 lb.-ft. from 3,500 to 4,500 rpm. It also allows the engine to meet strict low-emission vehicle (LEV) standards. It’s the only turbocharged engine to do so.
Next: Lamborghini Murcilago
LAMBORGHINI MURCILAGO: 12 ANGRY CYLINDERS
The all-new Lamborghini Murcilago, the latest and greatest ultimate Italian sports car, weighing in at $273,000, eschews turbochargers for 12 cylinders, double-overhead cams, and four valves per cylinder. Why a V12? Lamborghini’s Eleanora Negrin points out: “That’s what Lamborghinis have.”
Ah, tradition. “You can have a more powerful engine with the same displacement if you have more cylinders,” Negrin adds. It also helps that the Murcilago displaces 6.2 liters and has a maximum rpm-and reaches its peak power of 575 hp-at 7,500 rpm. Controlling all that might is as challenging as it is exhilarating; Road & Track likened being behind the wheel to standing at a railroad crossing as a freight train passed.
But the Murcilago, which replaces the Diablo for 2003, relies on more than size, multiple cylinders, and four dozen valves. It adds variable valve timing too. Unlike the GT2, the Murcilago adjusts both intake and exhaust camshafts, but to two positions only. The Lamborghini engine also uses a form of atmospheric supercharging to produce maximum peak power without sacrificing a broad torque curve. Lamborghini calls it variable-geometry intake.
Engine designers have long known about the resonance effect in an engine’s intake manifold. When the intake valve opens, the air inside is sucked into the cylinder. When the valve closes, air stuck inside the intake tract bounces against the closed valve and rebounds backward. After traveling the length of the tract, it hits the front of the intake manifold and heads toward the intake valve again. A clever engine builder can tune the length of the intake tract to precisely time the arrival of an incoming pulse with the valve opening. This natural supercharging packs slightly more intake air into the cylinder, increasing power.
If engineers were designing the Murcilago only for peak power, short intake tracts-timed for high rpm-would be fine. But the engine would be weak or even stumble at low rpm, with the pulses out of phase. Thus, Lamborghini counters with a butterfly valve that forces the intake through a longer bypass at low engine speeds, much as a trumpet valve changes a trumpet’s pitch.
It’s this unseen finesse that makes the Murcilago not only the Prince of the Autostrada, but a truly Italian sexy beast.
POWER FOR THE PEOPLE?
More demonstrations of pure power are coming. When the 2003 Mercedes-Benz SL55 hits dealerships later this year, it will combine mechanical supercharging and a 5.5-liter V8 to produce 493 hp. And the Maybach Type 12 sedan, also coming from Mercedes this year, will be powered by a twin-turbo 5.5-liter V12 engine rated at 550 hp and 660 lb.-ft. of torque.
An old racing adage answers the “How fast do you want to go?” question with another: “How much do you have to spend?” What separates the Vipers and Murcilagos from the Miatas and midlevel horsepower homages like the Chrysler 300M is engineering born of breeding and wealth. There’s no rational purpose to 500 horses or a 5,700-pound car-except to indulge the wealthy. As they say, money is power.