Since the reintroduction of its Dodge Challenger and Chevrolet Camaro competitors in the pony car segment, Ford’s Mustang has stacked up poorly when customers checked engine power numbers.
The Blue Oval’s 4.6-L SOHC, three-valves-per-cylinder V8 for 2009 was rated at 315 hp (235 kW), well short of the Camaro’s 426 hp (318 kW) and the Challenger’s 425 hp (317 kW). To rectify the situation, the company has developed a new 5.0-L V8 derived from the old engine’s architecture but with all new components.
The result is 412 hp (307 kW), almost as much power as from the larger-displacement Chevy and Dodge V8s. The installation of a supercharger for future specialty models such as the GT500 will boost power higher.
Souping up the existing engine meant that Ford could close most of the horsepower gap while adding only 10 more pounds (4.5 kg) of weight compared to its 4.6-L predecessor, reported Mustang Chief Engineer Dave Pericak.
At 430 lb (195 kg), the new 5.0-L V8 is more than 85 lb (39 kg) lighter than the old iron-block OHV 5.0-L V8 that powered Mustangs for decades.
In addition to adding nearly 100 hp (75 kW) to the engine’s output, Ford also expects the new 5.0-L will be more fuel efficient than the outgoing engine, which is EPA rated at 16 mpg city and 25 mpg highway.
Super-thin cylinder liners
The improvements are the result of optimized airflow, which is due to the application of a more sophisticated valvetrain and because of basic architectural changes to the engine. Rather than the previous single overhead camshaft per cylinder bank, the new 5.0-L V8 features double overhead cams which each employ independent continuously variable valve timing, which Ford brands “Ti-VCT.”
The cam phasers use engine torque, with assistance from engine oil pressure, to adjust valve timing. This arrangement allows the engine to use a conventional oil pressure pump that contributes to lower parasitic drag, compared with the higher-pressure oil pumps often used by variable valve timing systems.
Designers pushed the valve gear as far to the outside of the engine’s valley as possible, clearing space in the middle of the vee for unobstructed vertical intake passages. This created an engine with wide-open space in the middle, but one that crowds the engine bay on the sides. This resulted in packaging challenges for the exhaust manifolds and dipstick that required creative solutions.
Within the constraints of the engine’s foundation, Ford’s engineers wrung all of the displacement they could from the architecture, settling on a nearly square 92.2 x 92.7 mm bore and stroke (3.63 x 3.65 in), according to Pericak.
“It has every inch of displacement we could get out of it,” he said, adding that the V8 has the thinnest cylinder liners possible. Increasing the bore any further would require a sprayed-on liner, Pericak noted.
While some areas were slimmed to make room for bigger pistons, other parts of the engine were reinforced. The bulkheads are 2-mm (0.08-in) thicker than before for added strength. Larger, stronger fasteners also were used. The cylinder head bolts and the cross bolts on the six-bolt main bearing caps are both 1 mm (0.04-in) larger in diameter than before.
One technology that is absent from the 5.0-L engine is direct fuel injection. The reasons for this are a short development cycle, tight budget and marginal opportunity for improvement, reported Pericak.
“We had to go fast on the program, and direct injection is expensive and would have given us a small incremental gain,” he noted. Going to DI would enable a 12.0:1 compression ratio rather than the current 11.1:1 ratio, which would boost power only slightly, Pericak estimated.
Headers prototyped at home
In addition to adding displacement and boosting the flow of air into the engine, Ford’s engineers also streamlined the flow of air out of the engine. Its innovative tubular exhaust headers are credited with increasing output by 6 hp and 15 lb·ft (4.5 kW and 20 N·m, respectively), according to Adam Christian, the program's intake, exhaust and combustion engineer.
Working within the package constraints of the Mustang's engine-compartment space, Ford’s engineers were stumped by the challenge of designing extremely compact headers that would both minimize the effect of the destructive power pulses and maximize the effect of the beneficial ones.
Mulling the problem while in the shower, Christian had an epiphany. Rather than trying to create a header design that optimized the potentially useful exhaust pulses, he decided instead to create one that eliminated the power-robbing impact of the destructive ones, by simply pairing adjacent cylinders.
He carried some lengths of steel tubing home and welded up a prototype in his garage workshop. Two weeks later its effectiveness was proven out on the dyno.
Christian said he was motivated to devise the unorthodox solution by his team leader Mike Harrison, who told him, “Adam, just make it happen.”
The production tubular headers are manufactured by Benteler Automotive Corp. Christian admits that while their price premium compared to cast iron manifolds has caused some contention within the company, the power benefit is worth it.
The left-side header was also potentially fouled by the dipstick, until engineers contemplated an alternative route for it—through the cam cover and down an oil drain galley into the oil pan.
Retention of the original dipstick tube mounting boss in the block casting is evidence of other vehicle applications planned for the engine whose engine compartments are not so constrained for space.
Some of the hints include threaded-but-unused mounting bosses on the front of the right cylinder head casting. The gaping space within the valley of the engine’s vee and an unused drive pulley on the front of the crankshaft point to an upcoming, but as-yet unannounced, supercharged version of the 5.0-L.
Down in the depths of the engine, designers labored to optimize oil control to ensure lubrication under severe conditions while minimizing losses due to oil drag. In order to visually inspect how oil drainback would occur under high lateral acceleration, engineers installed clear camshaft covers on a prototype engine, which was rotated 90 degrees onto its side then run on the dyno.
With this set up, engineers observed the actual oil drain paths that would likely occur under racing or extreme track-day conditions.
In the oil pan, Dana Corp. provides a plastic crank scraper that is integrated into the pan gasket, a solution that simplifies assembly and reduces parts count while providing the benefit of reduced oil drag.