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2005 Shelby Cobra Concept
 
 
 
SHELBY COBRA’S NEW BITE: 605 HORSEPOWER
At the time Carroll Shelby began his Cobra project in 1962, England’s AC Cars had a beautiful little open-top car that needed an engine. Ford had the industry’s best family of V-8 engines. Shelby saw the possibilities and brought the two together. The rest is history.

"The Ford engines turned out to be a great choice," Shelby said. He first tried the 260- and 289-cubic-inch Ford small block V-8 engines before settling on the massive 427 as the ultimate Cobra engine.

For the next chapter in the Cobra legend, the modern Ford team also had a few powertrain options. They included the supercharged
5.4-liter V-8 from the Ford GT, as well as turbocharged 4.6-liter and 5.4-liter mills. Outstanding engines, yes, but they didn’t pack the spiritual punch of Shelby’s overpowering Ford 427.

They needed something more, something that would capture the essence of that 427 in a modern roadster. They found it in a satellite Ford engineering operation devoted to developing new powertrain technologies away from the narrower demands of product development.

In an atmosphere that is part think-tank and part speed-shop, the Advanced Powertrain team develops technologies that frequently have as many applications on the race track as in consumer vehicles.

For approximately two years, they had been working on an all-aluminum V-10 targeted at ultimate, naturally aspirated performance. When they bolted this beast into a Mustang chassis for evaluation, it only took one drive to confirm its potential.

"The Ford Shelby Cobra concept just begged for this engine," said Graham Hoare, director, 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."

Blending the Advanced Powertrain team’s work with elements from the 4.6-liter, 4-valve V-8 used in the 2004 Mustang Mach 1, the resultant Ford Shelby Cobra concept engine has 10 cylinders and is bored and stroked for a 6.4-liter displacement, or about 390 cubic inches. It produces 605 horsepower at 6,750 rpm and 501 foot-pounds of torque at 5,500 rpm without supercharging or turbocharging.

"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."

Kevin Byrd, the V-10 project leader, thinks of the Cobra V-10 as an all-star combination of current Ford engine technologies. "This engine is an amalgam of everything right about Ford engines. We took the best that the modular engine family has to offer, then added some tricks of our own. The V-10 is a culmination of 100 years of building engines," he said.

The double-overhead-cam cylinder heads and cylinders are fed by port fuel injection and racing-derived velocity stacks that are just visible within the hood scoop. For a low hood line, the throttles are a slide-plate design and the lubrication system is the dry-sump type, which relocates oil from underneath the engine to a remote tank. The engine proudly wears brushed aluminum "Powered By Ford" valve covers.

The rear-mounted six-speed transaxle is identical to the high-performance unit in the Ford GT, with an integral limited-slip differential to drive the rear wheels. Based on the engine’s 7,500-rpm redline and the drive ratios, this Ford Shelby Cobra concept has a theoretical top speed of more than 260 mph and would break 130 mph in third gear, although it’s electronically limited to 100 mph – for now.

Front-Mounted Engine and Torque Tube

One of the challenges of fitting a 10-cylinder engine into a compact roadster is leaving room for the driver’s legs and feet. With a conventional transmission mated to the back of the engine, the tradeoff between hood length and passenger room often makes for a cramped footwell and dramatically offset pedals – a flaw of the original Cobras and many modern sports cars.

Because the Ford Shelby Cobra concept was planned from the outset to be a production-feasible "runner," not just a pretty show car, the team had to address the legroom concern. They found that mounting the transmission at the rear of the car, connected to the front-mounted engine with a torque tube, let them use a very 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 stabilizes 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, Advanced Product Creation. "Using our electronic tools, we optimized 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."

 
Creating a New Chassis From Existing Parts
Although the AC Cars 260 roadster was the starting point for the original Cobra, the Ford Shelby Cobra concept team had no obvious existing architecture suitable for the project.

"We knew we wanted a front-engine car that had to be ultra-compact and lightweight, yet robust enough to handle 605 horsepower," said Theodore. "There was nothing that fit the bill on first glance."

But Rumpel’s team saw a creative solution.

"We were already planning to use the Ford GT suspension systems, and we asked ourselves how much more of the GT we could borrow," he said.

Quite a lot, as it turns out. Even though the GT is a mid-rear-engine car, and the proposed roadster was to have a front engine, a decision to mount the transmission at the rear made the connection.

"Once we really started looking into it, we had an epiphany," Theodore said. "The project took on a new sense of purpose when we really started leveraging the Ford GT engineering."

The team worked long hours with John Coletti, head of Ford’s Special Vehicle Team, to maximize the commonality. Fresh from completing the all-new Ford GT in just 15 months, Coletti understood what it took to build fast cars faster than ever. "It was a great team effort," Coletti said.

The bulk of the rear structure is made from slightly modified Ford GT components, including the massive, trellis-like cast aluminum suspension nodes, the rear rails and bumper beam, a major cross-member and the brackets used to mount the transmission.

The center portion of the space frame also has a high degree of GT commonality–major aluminum extrusions are based heavily on existing pieces. At the front of the roadster, the team incorporated the extruded main rails, steering rack cross-member, crash-management sections and the bumper beam.

"The concept car was even assembled using the prototype jigs the GT team no longer needed," said Rumpel. "This commonality and re-use goes hand-in-hand with our speed and cost efficiency."

Overall, the Ford Shelby Cobra concept is more than 2 feet shorter than the GT, with a wheelbase nearly 7 inches shorter. Even the track width has been reduced by more than an inch. That the concept car and the GT share any parts at all is a testimony to the flexibility of the space frame design and the creativity of the chassis team.

Ford GT Suspension, Steering and Brakes

To attach the massive 18- and 19-inch wheels and tires to the car, the team chose to use the Ford GT suspension system with a few modifications to accommodate the increased weight up front. Like engine technology and electronics, suspension design has come a long way in more than 40 years.

"The original leaf-sprung Cobras were awesome on the straightaway but didn’t make a name for themselves in the turns," said Rumpel.

Theodore was even more direct, "The original 427 was a beast."

The new Ford GT earns praise for its combination of agility, grip and easy-to-drive character, a reflection of its sophisticated suspension design and the expertise of its chassis engineers. The Ford Shelby Cobra concept applies the best of the GT suspension to a big-engine roadster.

A double-wishbone suspension design with unequal-length aluminum control arms, coil-over monotube shocks and stabilizer bars is used front and rear. The upper control arms are identical at all four wheels and are made with an advanced rheo-cast process that allows the complexity of form associated with casting, yet retaining the strength of forging. The metal, heated to just below its melting point, is the consistency of butter when it is injected into a mold at high pressure. Pressure is maintained as the part cures, preventing porosity in the final product for exceptional strength.

The steering rack also is borrowed from the Ford GT, with a few modifications. The steering column, like the Ford GT’s, draws on Ford engineering best-practices like the low friction, high stiffness and light weight that have made the Ford Focus steering column among the best in the industry. Braces between the front shock towers and below the isolated engine mounts improve torsional rigidity and aid steering response.

With more than 600 horsepower available at the throttle pedal, the brake pedal had to be equally potent. The team set braking distance targets comparable with today’s best sports cars, and turned to the Ford GT braking system for suitable components.

Brembo "monoblock" one-piece aluminum brake calipers with four pistons each grab cross-drilled, vented discs at all four wheels. The discs are a massive 14 inches in front and 13.2 inches in the rear, for fade-free stopping power. But the team stopped short of fitting the car with an antilock braking system, in keeping with its racing character. Brake balance is biased slightly to the front wheels to aid stability.

For packaging reasons, the team devised a novel offset actuation linkage for the brake booster and master cylinder, so the brake pedal can be placed in a normal position even though its hardware is off to the side of the engine bay.

The one-piece BBS wheels are wrapped by BF Goodrich Z-rated racing slicks, size 275/40R18 in front and 345/35R19 in the rear.

 
 
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