How Ford Designed a Brute That Doesn’t Guzzle

The Ward’s 10 Best Engines competition has recognized outstanding powertrain achievement for 19 years. In this installment of the 2013 Behind the 10 Best Engines series, WardsAuto looks at the development of Ford’s 5.8L supercharged DOHC V-8.

When Ford revived its legendary Shelby GT500 for the ’07 model year, that very hot Mustang was powered by a 5.4L 32-valve DOHC supercharged V-8 that was developed from the muscular “MOD” V-8 introduced in the ’00 limited-edition SVT Mustang Cobra R.

Force-fed to 8.5 psi (0.59 bar) by a screw-type supercharger, with piston rings and bearings from the Ford GT program, the engine featured aluminum heads, variable valve timing and upgraded cooling. It pumped out 500 hp, more than any factory Mustang before it, and 480 lb.-ft. (650 Nm) of torque.

“Wow!" exclaimed 82-year-old legendary racer and car builder Carroll Shelby at the time. "It feels like it has a lot more power than it has, and it gets it to the ground. This car, 40 years later, is everything I dreamed of when we built the originals."

Shelby died last year. But his memory lives on with a legacy of high-performance cars that bear his name. The latest is the ’13 GT500 powered by a new 662-hp 5.8L V-8, which earned a 2013 Ward's 10 Best Engines trophy in January.

Ford’s latest high-output V-8 is not a modified version of the excellent 5.0L that appears in both the Mustang and F-150 and won 10 Best Engines honors in 2011 and 2012. Instead, the new Shelby GT500 V-8 is based on the old iron-block 5.4L.

"The 5.0L is optimized as a naturally aspirated engine,” says Special Vehicle Team Powertrain Supervisor Jeff Albers. "This 5.8L was designed for a supercharged application and has a number of years of evolution going back to the ’07 GT500."

WardsAuto editors make no apologies for putting a special high-performance V-8 on the list. Its prodigious output “makes it the world’s most powerful production V-8, beating countless exotics costing many times more,” they say. But like so many others in the industry, they were shocked the big bruiser escaped the federal gas-guzzler tax.

How did Ford manage such a feat while so many other performance cars with less power have been socked with big guzzler penalties?

Albers says the development team set out with four clear-cut goals: 650 hp, 600 lb.-ft. (813 Nm) of torque, 200-mph (322 km/h) top speed and no gas-guzzler tax. That meant the new car had to be rated at a minimum combined, unadjusted 22.5 mpg (10.5 L/100 km).

To reach those goals, the team also had four strategies. The first was using a plasma-transfer-wire-arc process to replace conventional cylinder liners. Combined with a machining process called deck plate honing, engineers achieved near-perfect cylinder-bore geometry.

“By spraying a layer of steel onto the aluminum bore, we come very close to a true (perfectly round) cylinder, which allows us to reduce friction by using lower-tension rings,” Albers says.

This process, first used on the 5.4L, also saves weight and improves heat transfer to the coolant.

The second tactic was increasing the compression ratio to 9:1 from the previous 8.4:1, which involved some risk. “Higher compression leads to higher efficiency, but with a supercharged engine, you need to be careful not to get into temperature sensitivity, which can lead to pre-ignition,” Albers says.

The third line of attack involved the use of oil jets to cool the pistons. The oil squirters were added mainly to improve engine durability, but they offer another perk: Because they speed heat transfer to the lubricant, the whole engine warms up faster during cold starts.

“That is a real benefit for customers,” Albers says. “Fuel efficiency for the first few miles is better because the oil is warmer and has lower friction than it would without the squirters.”

The fourth strategy for improving efficiency targeted the drive schedule used for Environmental Protection Agency fuel-economy testing.

“This engine has a very flat torque curve,” Albers says. “It delivers a lot of torque at low rpms, which enables a certain driving style. You can be in a relatively high gear and, with very little (throttle) tip-in; you can get incredible acceleration, which promotes a driving style that is fairly fuel-efficient.”

But doesn't the EPA test procedure specify gears, not just speeds?

“There are two ways you can go,” Albers says. “You can use the standard EPA shift schedule, or you can have a bunch of drivers drive the vehicle over a prescribed test route and collect data on how they drive it. That data then is reduced to a shift schedule that, for an engine with so much low-end torque, tends to be better than the standard schedule. So you can run this shift survey and get a schedule that is representative of how people actually drive your vehicle.”

Engineers combined these actions with body and chassis improvements, such as low-friction axle lube and a single-piece carbon-fiber drive shaft that eliminates center bearing friction, and came up with an EPA (adjusted) rating of 15/24 mpg (15.7-9.8 L/100 km) city/highway. 

Hitting the fuel-efficiency goal was tough, but achieving the output objectives while ensuring durability were big challenges as well. The team came up short initially on the former so engineers started looking at ways to increase airflow. That led to higher-lift camshafts, changing the supercharger drive ratio and modifying the air induction system.

“We spent a lot of time doing CFD (computational fluid dynamics) analysis on the air induction system and the supercharger inlet,” Albers says. “We started with an Eaton TVS (twin vortex series) set-up, did some extensive analysis and found that if we modified the inlet and the spacer between the throttle body and the supercharger, we could get a significant increase in airflow.”

Maximum supercharger boost also was bumped to 14 psi (0.97 bar) to get the needed increase in power. Turbocharging was not considered.

Despite major achievements in fuel efficiency and specific output, Albers won’t rule out more gains down the road. “Engineers are never happy to put their pencils down,” he says.

“There always is something they wouldn't mind going after. And if money is no object, there is always more to be had. It comes down to a value proposition. Is there enough benefit for the investment it would take?”

Gasoline direct injection is a possibility for the next-generation engine. It was seriously considered during this go-round but ultimately rejected.

“You can get maybe another half-point of compression out of it, which would give a little efficiency improvement. But we did a lot of modeling and projections on where we needed to be, and direct injection was not necessary to achieve our goals,” Albers says.

“We had to choose where to spend our investment funds, and we elected to spend it elsewhere. (DI) tends to be designed in when there is major architectural change.”