[Source: Ford press release]

“Developing the Ford GT from approval to drivable production models in less than a year is quite a challenge,” says Neil Hannemann, chief program engineer for the Ford GT. “But these three cars serve as a testament to the passion and expertise of Ford engineering.”

Stiff Aluminum Space Frame

Usually a new vehicle is designed from the inside out, meaning that the chassis and suspension points are set before the exterior body is designed around those dimensions. The exact opposite is true of the Ford GT. To preserve the design of the Ford GT40 concept car shown at the 2002 North American International Auto Show, the Ford GT engineering team is doing most of its work “under the skin.”

“The first step in creating a world-class supercar is creating a stiff structure,” says Huibert Mees, chassis supervisor on the Ford GT program. Mees set contradictory targets for the chassis: extremely high torsional stiffness for unparalleled body control, yet efficient use of materials, necessary for a lightweight chassis to reach performance and handling targets.

The team developed an all-aluminum space frame, comprising 35 extrusions, seven complex castings, two semi-solid formed castings, and various stamped aluminum panels. The structure has two unique features: A large center tunnel to house the mid-mounted fuel tank and cut-out roof sections for the cantilevered doors.

“Using CAD/CAM and finite-element analysis, we were able to design and test several iterations of the fuel tunnel and roof structure,” says Mees. “That process enabled us to add significant stiffness to the overall structure.”

Another contributor to chassis rigidity is the industry's first application of friction-stir welding, used to construct the multi-piece central aluminum tunnel (housing the fuel tank). With this technique, a tool rotating at 10,000 rpm applies pressure to a seam and actually blends the metal there, forming a smooth, consistent seam.

Compared to automated MIG welding, friction-stir welding improves the dimensional accuracy of the assembly, and produces a 30 percent increase in joint strength. And because the seam is continuous, the technique effectively isolates the fuel tank from the passenger compartment. A patent application is pending on this new friction-stir welding process.

Once the structure of the hybrid-aluminum design was approved, Mees' team addressed each component to maximize strength and minimize weight. As a result, larger extrusions such as the primary frame rails have a different thickness on each wall. Portholes or windows in the complex castings – which support the suspension and powertrain – decrease unnecessary mass. Even the small castings that join the A-pillars to the roof have been fine-tuned for utmost rigidity and lightness.

“The results are astounding,” Mees says. “In our tests, the Ford GT chassis is stiffer and more rigid than the current competitive set. Indeed, we predict it will be better than upcoming competitors as well.”

Extensive use of computer-aided crash modeling during the design phase helped the Ford GT program team cut cost and time during the early stages of development. The crash analyses were used to predict the forces generated during impacts and the resulting shapes of the crushed structures without the costly and time-consuming destruction of hand-built prototypes.

As a result of these analyses, the front and rear bumpers are connected to the frame via extruded aluminum “crush rails” that accordion during impact. These rails are designed to absorb most of the damage during low-speed impacts and are bolted to the frame for easy removal and replacement.

Fuel system

Crash modeling also verified that the center tunnel is the preferred location for the Ford GT fuel tank because it helps reduce risks, most notably in collisions. As an added benefit, the location keeps overall weight distribution and the center of gravity relatively consistent at differing fuel levels. The “ship-in-a-bottle” design of the fuel tank is an industry first. The mechanical components, including the fuel pumps, level sensors and vapor control valves are first mounted on a steel rail. Then, the single-piece tank is blow-molded around the rail. This method maximizes fuel volume and reduces the number of connections to the fuel system.

As another industry first, the Ford GT features a capless fuel filler neck under an aluminum cover. The aperture automatically opens as the fuel nozzle is inserted and seals the fuel system when the nozzle is removed.

High-tech Body

Most aluminum space frame vehicles use nut inserts paired with shims or washers to tailor the fitment of each body panel. However, the Ford GT team developed a novel new method, called a “plus-nut,” to efficiently join the body and frame, as well as locate the body panels in the proper position relative to the space frame.

These fasteners are essentially aluminum nut inserts, with additional machining stock on the mating surface. While machining the suspension and engine mounts, Computer Numeric Controlled (CNC) milling accurately trims each aluminum plus-nut for precise body positioning. The patent-pending fasteners eliminate the need for shimming the body, reducing assembly costs and improving panel fit.

The aluminum body panels themselves are also fairly advanced, manufactured using super plastic forming (SPF). “Super plastic forming is fairly new for the industry,” says Bill Clarke, Ford GT body structure supervisor. “It was a critical factor in producing the large sections, complex shapes and delicate accent lines of the concept vehicle. Large, intricate panels like the cantilevered doors simply would not have been feasible with traditional stampings.”

Rather than using a matched metal die to stamp the body panels, super plastic forming works by heating an aluminum panel to temperatures near 950 degrees Fahrenheit (approximately 500 degrees Celsius), then using high-pressure air to plastically form the aluminum panel over a single-sided die. This process produces complex shapes not possible with conventional stamping and reduces tooling costs since only a single-sided die is required.

According to Clarke, the super plastic forming also reduced production complexity. “As an example, with super plastic forming we were able to make the exterior of the rear clamshell in one piece,” he says. “The same panel with traditional manufacturing would require five or six separate stampings joined together on the assembly line.”

The rear clamshell engine cover also represents another industry first: It features an aluminum shell hemmed to a carbon-fiber inner panel. The carbon-fiber piece is lightweight and extremely rigid, which helps stabilize the clamshell. In addition, the inner panel houses an air duct into the engine air box from the exterior intake just below the C-pillar.

Aerodynamic Development

Like the concept car, every air intake and heat extractor on the production Ford GT is functional. According to Kent Harrison, Ford GT performance development supervisor, preliminary wind-tunnel testing showed the concept car had remarkably good internal air flow.

“We first tested a fiberglass replica of the concept car in the wind tunnel,” says Harrison. “Because the design was so close to that of the Ford GT race cars, the intakes and diffusers were all in the right place. We only needed minor changes to improve air flow through the car.”

The heat extractors in the front cowl were modified to pull more heat from the front-mounted radiators. The side intakes under the B-pillar were slightly enlarged, driving more cooling air into the engine bay and transmission cooler. Finally, an additional set of vents on either side of the rear glass help diffuse heat from the engine compartment.

However, improving the aerodynamic stability was not such an easy task. The team also tested an original Ford GT race car in the wind tunnel, and with computer simulations, to measure drag, lift, and downforce. To their surprise, the original car exhibited very high frontal lift at speed.

“The whole team had an even greater respect for the drivers who took the original car down the Mulsanne straight at over 200 mph … at night … in the rain,” says Harrison. “Because the new design shared a similar design, the new aero model exhibited similar lift. We had to do something for more downforce.”

However, to preserve the design of the concept car, Harrison had to concentrate on the underside of the vehicle. Harrison's team added a front splitter, which creates a high-pressure area for front downforce, and limits the volume of air traveling under the vehicle. They also added side splitters to prevent air from sliding under the rocker panels. A smooth, enclosed belly pan reduces underbody turbulence. Finally, venturi tunnels accelerate exiting air, creating a vacuum that literally sucks the car to the pavement. The cumulative result is significant downforce at speed and one of the most efficient lift/drag values on a production car.

Double-wishbone Suspension

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 the same at each corner. They are made with an advanced rheo-cast process that allows the complexity of form associated with casting while 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.

“We knew from the beginning that the new Ford GT was going to be a road car, not a race car, so that helped us quickly design the suspension,” says Tom Reichenbach, vehicle engineering manager for Ford GT. Tapping into his personal racing experience and his knowledge from working on a Ford’s Formula One team, Reichenbach knew the obstacles and opportunities ahead of him. “We’ve managed to build a world-class supercar on a race team schedule,” he says. “As they say in motorsports, ‘The other teams won’t wait for you at the starting line.’”

Brembo one-piece 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. Anti-lock control and electronic brake force distribution help provide consistent, straight braking even from very high speeds.

One-piece BBS wheels are wrapped by Goodyear Eagle F1 Supercar tires, size 235/45ZR-18 in front and 315/40ZR-19 in the rear.

Supercharged 5.4-liter V-8

The Ford GT is driven by an all-new, mid-engined powertrain producing 500 horsepower and 500 foot-pounds of torque. The engine architecture comes from Ford’s MOD engine family, which includes performance powertrains like the 390-horsepower 4.6-liter DOHC supercharged V-8 in the SVT Mustang Cobra and the 380-horsepower 5.4-liter SOHC supercharged V-8 in the SVT F-150 Lightning.

“We're just starting to tap the performance potential of Ford's modular engine architecture,” says Curt Hill, Ford GT powertrain engineering supervisor. “This application really demonstrates its awesome potential. The 5.4-liter engine easily produces 500 horsepower and 500 foot-pounds of torque, while meeting all the current emissions and durability standards. Those numbers are comparable to the race-prepared, blue-printed 427 (7.0-liter) big-blocks in the Ford GT race cars.”

The Ford GT engine features an all-new, aluminum block fitted with high-flow, four-valve cylinder heads and dual overhead camshafts. To bear the stresses necessary to produce 500 horsepower, a forged-steel crankshaft, shot-peened H-beam connecting rods and forged aluminum pistons are used. “In total, 85 percent of the reciprocating parts are unique to the Ford GT,” says Hill.

Fuel is delivered via dual fuel injectors per cylinder. A modified screw-type supercharger blowing through a water-to-air intercooler supplies sufficient airflow for engine output.

Hill's team specified two race-inspired powertrain components, a dry-sump oil system and a twin-plate clutch. The high-capacity, dry-sump oil system provides consistent lubrication, even during maximum handling. The twin-plate clutch delivers low pedal efforts while still providing the clamp loads necessary to handle 500 foot-pounds of torque. More significantly, these two features allow the powertrain to sit more than 4 inches lower in the frame as compared with the front-engined SVT Mustang Cobra. This helped maintain the low design profile and keep the car’s center of gravity low for better handling. Backing the clutch is an all-new, six-speed transaxle from Ricardo. The clean-sheet design enabled Ford engineers to tailor the individual ratios to their specifications, without being forced to select from an existing assortment. The transmission is fully synchronized and features an integral, torque-sensing, limited-slip differential.

Digitally-mastered Interior

To maximize passenger comfort, Ford GT chief designer – Camilo Pardo – and the engineering team made extensive use of a virtual-reality computer-modeling device called the digital occupant buck. The device is a revolutionary step in CAD/CAM technology with a virtual re-creation of the interior surfaces translated from the CAD data; a physical mock-up of the seat, steering wheel and pedal assembly; and a test engineer fitted with magnetic sensors, which manipulate a virtual person inserted in the digital interior. “The real advantage of digital occupant is that it allows engineers to develop a comfortable interior for a wide range of statures,” according to Kip Ewing, supervisor of package, prototype and launch for the Ford GT. “As an example, I could sit in the Ford GT seats as a fifth-percentile female, and evaluate her reach to major controls. Five minutes later, I could sit in the car as a ninety-fifth-percentile male and evaluate his outward visibility.”

As a result of this testing, Ewing tweaked the occupant package for the maximum range of accommodation. This included obvious improvements, such as maximizing seat travel and headroom. But he also made other subtle improvements, like centering the pedal package relative to the driver's seat, and canting the shift lever toward the driver.

For Coletti, technology like the digital occupant buck and patented body fasteners are what make the Ford GT stand out. “Any company can take a concept car and turn it into a crude, limited-edition production car,” he says. “But the craftsmanship and technology of the Ford GT make it a world-class supercar. It's a testament to the engineering expertise and technological resources that are taking Ford Motor Company into the future.”