Ford's limited-production SVT Mustang Cobra R has a top speed of more than 274 km/h (170 mph) and can attain greater than 1.0 g on the 30-m (100-ft) skidpad. The Cobra R's 5.4-L V8 produces 287 kW (385 hp) at 6250 rpm and 522 Nom (385 lboft) at 4250 rpm, with specific output of 53.2 kW/L (71.3 hp/L). Cobra R's interior features front Recaro seats, while the rear seat is eliminated-replaced with a closure panel that covers the floor pan The Cobra R's brakes got engineering attention in the form of four-piston Brembo calipers for the 330-mm (13-in) front brake rotors and race-proven carbon fiber air ducts to cool the front rotors. Also shown are the car's Bilstein dampers and Eibach springs. Optimized Cobra R airflow details: a unique rear spoiler for high-speed stability; air ducts in the front fascia to cool the front brake rotors; and side-exit exhaust pipes.

"Everything we've done on this car is a notch, or several notches, above anything we've done before," said John Coletti, Ford Special Vehicle Engineering (SVE) Manager. "This 2000 Cobra R pushes the performance envelope far beyond the capabilities of any previous Mustang. One of our goals is to make the Ford modular engine family the performance benchmark of the industry. This application demonstrates its real potential. This engine is street-legal, EPA-certified, and very driveable for its high power output."

The Cobra R's V8 engine produces 287 kW (385 hp) at 6250 rpm and 522 Nom (385 lboft) at 4250 rpm. It is based on Ford's Triton 5.4-L cast-iron modular block with forged-steel crankshaft. Its cylinder bore is the same as the 4.6-L aluminum-block engine's, but its block deck height is 29 mm (1.1 in) taller. This allowed the stroke to be extended by 15.8 mm (0.62 in)-105.8 vs. 90.0 mm (4.17 vs. 3.54 in)-and accounts for the increased displacement. New engine mounts and a lowered crossmember were required to lower the engine 12 mm (0.47 in) inside the body to fit the taller engine.

The engine's forged crankshaft is fitted with Federal-Mogul rod bearings, Carrillo billet-steel connecting rods, and forged-aluminum pistons. The pistons are similar to those found in the SVT Lightning, but are modified with increased wall and pin strength for higher engine speeds and flat tops to increase compression ratio to 9.60:1. The engine also has a new crankshaft vibration damper tuned for the increased firing loads and higher rpm. At the bottom of the engine, a high-volume Canton Racing Products oil pan with internal baffle system maintains a consistent oil supply under the high cornering forces of racing. The company also provides a windage tray for reduced oil aeration and increased power.

Ed Olin, Systems Engineer at Ford's Advanced Powertrain Engineering, who oversaw the powerplant's development, said the specially designed four-valve cylinder heads are the key to the engine's power. "Initially we used DOHC heads that were designed for Ford's Rough Riders off-road truck racing program," said Olin. "That was a major help and it really paved the way for our work. Initial development was a success, but because of tooling limitations we had to design new heads for the Cobra R. They're similar to the 4.6-L Cobra heads, but with a lot more flow through the intake and exhaust ports."

Engineers achieved a peak airflow increase of greater than 25% by reshaping the intake and exhaust ports, redesigning the intake and exhaust valves, and increasing exhaust-valve diameter by 2 mm (0.08 in) compared with the 4.6-L engine. Camshafts are similar to the 4.6-L Cobra's, but they have more aggressive opening and closing rates and higher lift. Intake- and exhaust-valve lifts are 13 and 12 mm (0.51 and 0.47 in), respectively, versus the 4.6-L's 10 mm (0.39 in) for both. The cylinder heads are secured to the block with special high-strength bolts, and the primary timing chains are production 5.4-L units, micro-polished for high-speed use and high-load durability. Air enters the engine through a K&N cylindrical filter. The throttle body is a new, larger, oval-shaped single-bore version of the Cobra's dual-bore unit. The low-restriction intake manifold is a two-piece design with a bolt-on plenum cover. Engineers used computer modeling for tuning and flow optimization to produce a manifold with runners that have minimal bends. The exhaust manifolds use a tubular steel, short-tube header design that fits into a Bassani X-pipe with production Cobra catalytic converters.

The engine's specific output is 53.2 kW/L (71.3 hp/L) compared with 38.6 (51.7) for the previous 5.8-L Cobra R, 51.8 (69.5) for the current 4.6-L Cobra, and 41.4 (55.5) for the 5.4-L Lincoln Navigator engine. Since Cobra R engines have many unique components and the production run is just 300 units, they were built as part of a large prototype program at Ford's Engine Manufacturing Development Operations (EMDO). Each engine was hand built, and EMDO personnel also performed all the cylinder head machining, camshaft production, as well as general parts storage and coordination. Several components in the drivetrain were upgraded to handle the engine's greater power and torque. The engine is mated to a Mustang-first six-speed manual transmission. The Tremec T-56 gearbox provides closer ratios and added robustness for racing.

Visteon supplies the speed- and torque-sensitive hydromechanical differential, which gives the car more predictable performance and improved torque-transfer capability. Speed sensitivity is provided by a gerotor pump. When one of the halfshafts rotates at a greater speed than the other, the pump applies hydraulic pressure to compress the clutch pack and transfer torque to the other wheel. The differential's torque sensitivity helps maintain grip during straight-line acceleration. When one wheel spins relative to the other, the differential's beveled helical gears produce an axial force that, like the gerotor pump's action, compresses the clutch pack to transfer torque.

The Cobra R's final drive ratio is 3.55:1 (vs. the Cobra's 3.27:1) and its rear axle halfshafts have been redesigned. The induction-hardened GKN units have the same shaft diameter as those in the Cobra, but their inner splines have 31 teeth instead of 28, the inner tulips are a tripod design, and the right-side shaft is shorter to accommodate the larger differential.

The SVE team re-engineered the Cobra R's suspension to cope with the higher power output. The suspension follows the SVT tuning philosophy for road cars-compliant and subtle-but at a much higher level, with a strong emphasis on race-track handling. The engineers optimized tuning to balance center of gravity height, aerodynamic downforce, ride height, overall grip on bumpy roads, and driving ease at the limit. The result is a lateral acceleration measurement over 1.0 g on the 30-m (100-ft) skidpad, compared to 0.89 g for the 1999 Cobra.

Eibach coil springs lower the Cobra R 38 mm (1.5 in) in front and 25 mm (1.0 in) at the rear, and spring rates are 30-40% stiffer: 140 vs. 88 N/mm (800 vs. 500 lb/in) in front and 131 vs. 82 N/mm (750 vs. 470 lb/in) at the rear. Bilstein shock absorbers with digressive valving are used, with front gas-charged monotube units and rear gas-charged twin-tube types. Front and rear stabilizer bars are carried over from the Cobra.

The Cobra R's suspension control arm and rear subframe bushings are made of stiffer material, which improves handling by reducing compliance-steer during the higher cornering, acceleration, and braking forces generated in racing. In addition, the outer pivot of the upper control arm has been relocated to provide increased camber.

Though it is equipped with fundamentally the same steering package as the Cobra-a rack-and-pinion system with 15:1 ratio and 2.5 turns lock-to-lock-the Cobra R's boost curve has been revised to give a more precise overall feel. The rack's stops are revised to accommodate the larger wheels and tires and lowered ride height. The tie rod ends have been lowered 4 mm (0.16 in) to decrease the bump-steer effects caused by the car's lowered ride height. Power steering fluid is cooled by an air-to-oil cooler behind the front fascia and a water-to-oil cooler integrated with the engine radiator.

Braking capabilities were improved by fitting the Cobra's Brembo 330-mm (13-in) vented front rotors with four-piston aluminum calipers. Air inlets in the former front fog light openings attach to ducts that rout air to special carbon-fiber heat shields fitted around the inside of the brakes to cool the rotors. Rear rotors and calipers are unchanged from the Cobra, but 1-mm (0.04-in) thicker racing pads have been specified. Larger 18 x 9.5-inch, five-spoke aluminum wheels provide the extra clearance required for the larger front brake calipers. Specially manufactured 265/40ZR-18 BFGoodrich g-ForceKD tires help provide the level of handling and roadholding specified by SVE team.

Cobra R's basic body structure is the same as any other Mustang, though some items-including all chassis sound damping material, trunk trim, spare tire cover, the rear seat and rear trim-were deleted to reduce weight and enhance performance. The car's 79-L (21-gal) "fuel cell," produced by Fuel Safe for the Cobra R, uses the same mounting points as the stock tank. The rear deck and fascia are the same as used on the Mustang V6 model, and a specially designed rear wing and front splitter (along with the lowered ride height) reduce front lift and increase rear downforce, aiding aerodynamic stability up to the car's top speed of more than 275 km/h (170 mph). The splitter virtually eliminates front-end lift above 160 km/h (100 mph). The Cobra's "power dome" hood provides the extra clearance necessary for the engine's intake system.

Kevin Jost

AEI September 2000