Ford uncoils its Cobra

By ALASTAIR SLOANE motoring editor

It weighs around 1360kg and is about as long as a Mazda MX-5. There is no roof, no side windows, not even a radio. And the engine is a beast, a 450kW V10 with a theoretical top speed of 420km/h. "That's the formula," said Carroll Shelby. "It's a massive motor in a tiny, lightweight car."

The Ford Shelby Cobra GT was one of the worst-kept secrets of the Detroit motor show. The roadster, says Ford, marks the latest step in an exciting evolution of Ford concept vehicles, with a level of feasibility that is already close to production-level.

The debut of the Cobra GT concept followed the unveiling of the production version of the new Mustang. Both cars come after the appearance last year of the Ford GT, the spiritual successor to the GT40.

Will the Cobra concept also make it into production? Ford design director J. Mays told reporters: "We built the Ford GT a year after we showed the concept and we built the Mustang a year after we showed that concept. You do the math. If we get the same overwhelming reaction to the Cobra concept as we did to the GT concept, anything is possible."

The production model would get roll-up windows, a removable soft top, and rear-view mirrors. What about a radio? Maybe not, says Cobra designer Richard Hutting. "The tuned exhaust makes its own music."

The reborn roadster borrows heavily from the Ford GT parts bin - wishbone suspension, space frame, transaxle, brakes, and so on - and has been inspired by the biggest, baddest Cobra of them all, the legendary 427.

It is intentionally similar to the original model of 1962, conceived when American race driver Shelby shoehorned Ford V8s into a sportscar body made by British company AC.

The big grille opening remains, so do the round headlights, stacked tail-lights, side air extractors, low-back seats and bulging wheel arches.

But Mays says the new car isn't a "retro" design, it is more one of "heritage". While there are obvious similarities, the modern concept shares none of its dimensions or proportions with the original.

"When you're setting out to tell a story about an automobile in a fresh, contemporary way, you're not looking to create beauty, you're looking to create meaning," said Mays. "We have interpreted that raw, aggressive Cobra attitude in a very modern way.

"What we're trying to do is not just take the [show] audience somewhere they haven't been in a very long time, but take them somewhere they've never been, and there's a lot of magic in trying to do that," Mays said.

Like Shelby in the 1960s, the modern Cobra concept team had a handful of powertrain options, including the supercharged 5.4-litre V8 from the Ford GT, as well as turbocharged 4.6-litre and 5.4-litre units. But they didn't pack the spiritual punch of Shelby's Ford 427.

They needed something more, something that would capture the essence of the 427 in a modern roadster. They found it in an all-aluminium, naturally aspirated V10 Ford engineers had been working on for two years. They bolted it into a Mustang chassis and one drive confirmed its potential.

"The Cobra concept just begged for this engine," said Graham Hoare, director of Ford research and advanced engineering.

"Although it's not yet ready for production, we've reached a credible engineering level for such a serious concept car and it has a modern soul that matches the famous 427."

The 40-valve V10 has a displacement of 6.4-litres (about 390ci) and uses components from the 4.6-litre, 4-valve V8 used in the 2004 Mustang Mach 1.

It produces 450kW (605bhp) at 6750rpm and 680Nm (501 lb-ft) at 5500rpm through the car's 19-inch rear wheels via a six-speed gearbox and limited-slip differential. That's enough to launch it from 0-60 in under 4 seconds and deliver an ungoverned top speed of 307km/h (190mph).

"In many ways, it's not very exotic," said Hoare. "It uses the same basic castings and assembly techniques as our production modular engine family. The output, though, is phenomenal. If you can't get in trouble with this kind of power, you're not trying hard enough."

Ford says based on the engine's 7500-rpm redline and the drive ratios, the Cobra concept has a theoretical top speed of more than 260mph (420km/h) and would break 130mph (210km/h) in third gear, although it is electronically limited to 100mph (162km/h) for now.

One of the challenges Ford faced in fitting a V10 engine in a compact roadster was leaving room for the driver's and passenger's legs. That's why it mounted the six-speed gearbox at the rear of the car, connected to the engine up front with a torque tube-style driveshaft running in a narrow tunnel between the seats.

Compared to a conventional driveshaft, which is typically mounted behind the transmission, a torque tube-style driveshaft spins considerably faster because it is running at engine speed. The spinning inner shaft is supported within a stationary outer tube that stabilises the engine and transmission in bending and in torsion. The inner shaft taps crankshaft torque via a twin-disc, small-diameter clutch mounted at the rear of the engine.

Computer-aided design was essential in helping the first prototype come together smoothly. "Because they spin so much faster than driveshafts, these torque tubes can be a nightmare in terms of vibration," said Manfred Rumpel, manager of advanced product creation.

"Using our electronic tools, we optimised the location of the driveshaft support bearings and it ran smoothly on the very first try. This type of modern engineering tool gives us a development advantage that pioneers like Carroll Shelby could only dream about."

* The first 75 Cobras Shelby built in the early 1960s were powered by Ford's 260-cubic-inch (4.2-litre) V-8; 51 more used the larger and more powerful 289ci (4.7-litre) engine.

Shelby first installed the Ford 427 (7-litre) engine in the Cobra in October 1963, but the combination of the powerful engine and the rear leaf-spring suspension made the car treacherous to drive.

Ford helped Shelby to completely redesign the chassis, including an all-new coil-spring rear suspension and, by January 1965, Shelby introduced the production 427 Cobra, the car many enthusiasts herald as the ultimate street-legal racer.

"Our original objective was to build a sports car that would outrun [Chevrolet] Corvette," Shelby said. "I never dreamed it would become the icon that it did."