Ford Duratec 35 Thrives On Simplicity

The Ward’s 10 Best Engines celebrates 13 years of recognizing outstanding powertrain development. In this first of a series, Ward’s highlights the packaging and cost challenges that faced Ford engineers working on the new Duratec 35 V-6. Watch for features on the other 2007 winners throughout the year.

In an industry scrambling to manage the fusion of electronics and mechanical components, you don’t hear much anymore about simplicity. Largely because things aren’t.

Yet that’s one of the design attributes of which Ford Motor Co.’s engineers are most proud when looking back at the development of the all-new Duratec 35 3.5L DOHC V-6, a Ward’s 10 Best Engines winner in its first year of production.

The desire to keep it simple – but make it world class – led to an award-winning V-6 that’s got a big future at Ford. The company says the Duratec 35 eventually will power 20% of all the vehicles it sells.

“One of the things I’ve been very happy with is, I really believe we delivered an engine that is less complicated (than competitive V-6s),” Tom McCarthy, manager-V-6 engine programs, says.

From the beginning, Ford’s engine designers and engineers set out to develop an all-new V-6 engine family that is “good from a functional standpoint but is relatively simple,” he says.

McCarthy says because almost everyone – from executives and engineers and eventually, the customer – expects complicated systems and controls, it can be a challenge to make a new engine appear competitive without a host of intricate features and add-ons.

He says it might be easy to consider what the Duratec 35 lacks, for instance, variable valve timing for the exhaust camshafts and manifold swirl valves, and say, “’Why doesn’t it have this widget?’ Because you don’t need it,” McCarthy insists.

He credits intensive development of the Duratec 35’s foundation components for the engine’s excellent performance and responsiveness, both of which Ward’s editors say strongly contributed to the new V-6’s 10 Best Engines win.

At 265 hp at 6,250 rpm and 250 lb.-ft. (339 Nm) of torque at 4,500 rpm when fitted in Ford’s all-new Edge and Lincoln MKX cross/utility vehicles, the Duratec 35 is easily on pace with the growing cadre of high-volume V-6s from both import and domestic auto makers.

Perhaps more impressive, those numbers threaten premium-brand V-6s of similar displacement.

McCarthy says the Duratec 35 owes its intrinsic goodness to intensive computer-aided engineering, saying the engine’s development was “the most aggressive application of analytical tools” yet for Ford Powertrain.

McCarthy says competitive 3.5L V-6s in premium trim have higher specific output, but that’s easier to achieve when those V-6s usually are fitted in a longitudinal orientation for rear-wheel-drive layouts, where there typically is less exhaust restriction.

And it’s practically a given that premium unleaded fuel is required to achieve maximum performance.

At 76 hp/L, the Duratec 35 beats or equals volume-production, transversely-mounted V-6 competitors such as Honda’s 3.5L SOHC V-6 (71 hp/L); Nissan’s 3.5L DOHC V-6 (69 hp/L); and GM’s 3.6L DOHC V-6 (76 hp/L).

The Duratec 35 also bests the power density of the GM 3.6L unit when fitted in a RWD Cadillac car, and it runs in the same league with Mercedes-Benz’s 3.5L DOHC V-6 (77 hp/L); and Lexus and Infiniti 3.5L dual-cam V-6s, both of which develop class-leading 87 hp/L.

“We used a lot of design for Six Sigma,” he adds of the approximately 3-year development program, stressing that design quality is as important as big horsepower and torque figures.

He says the Duratec 35’s outstanding noise, vibration and harshness (NVH) characteristics – not to mention its entertaining 6,700-rpm redline and ability to use regular unleaded gasoline despite its high, power- and efficiency-enhancing 10.3:1 compression ratio – are benefits from the long hours of CAE.

“You look at the kind of energy you put into the lower part of the engine,” he says of early goals to achieve structural rigidity and low friction.

Engineers and developers insisted, in particular, on a highly rigid structure for the all-aluminum block and forged-steel crankshaft. The end result was “uncompromised crank stiffness,” he says, one of the first rules of quality engine design.

For a high-volume engine, the Duratec 35 sports some components that could be deemed almost extravagant. Items such as the fully isolated cam covers stamped from aluminum instead of the now-typical, and less costly, plastic.

McCarthy says engineers and designers made careful decisions in matters of cost vs. desired NVH, performance and quality attributes. It’s a process not for the squeamish.

“We do a cost study (of almost every engine component),” he says. The ultimate variable cost for the engine “has to be reviewed all the way up to the board of directors. It’s a balancing act – and there are going to be tradeoffs.”

Fighting the good fight to ensure competitive NVH and performance levels while remaining within cost boundaries is but one aspect of what it takes to bring an award-winning new engine to market.

Engineers also struggled daily with design constraints that included a need to make the Duratec 35 fit in the basic space required for the smaller 3L Duratec 30, which is a completely different architecture.

Esoterica such as deck height, crankcase width, adaptability for all-wheel drive and transmission modularity had to fit the mandate of keeping the larger 3.5L V-6 the same size as the older 3L Duratec in every dimension except for length.

“You literally have to count, millimeter by millimeter, of real estate,” McCarthy says. The design team had to guarantee the Duratec 35 would fit between the frame rails of the wide variety of vehicle architectures for which the new V-6 is earmarked.

He says the engine developers coordinate with engineers for all the targeted vehicle platforms to ensure “functionals” and identify possible future needs.

“You do it with as many potential ‘users’ as possible,” he says, adding that in these times of complex platform and powertrain sharing, cooperation often doesn’t just mean with the folks in the next building. “In this case, Mazda (Motor Corp.) was one of the customers as well.

“One of the things I think we also did well is work with the manufacturing team,” McCarthy says. The Duratec 35 is built at Ford’s Lima Engine Plant in Lima, OH.

“There were a couple of levels of success on this program,” he adds, including cooperation with suppliers. McCarthy chooses not to single out any individual suppliers, diplomatically praising one and all.

“The suppliers we had on this program really came through for us,” he says.

Although 2007’s Ward’s 10 Best Engines award is a satisfying validation in the engine’s launch year, there is more to come. McCarthy says part and parcel of a contemporary engine development process is “protecting” the design for future upgrades and technology.

He confirms variable timing for exhaust valves is a likely future upgrade, but he won’t offer a juicier look in the crystal ball, such as details of the “TwinForce” turbocharged, direct-injection concept engine based on the Duratec 35 and shown in the Lincoln MKR concept car at January’s North American International Auto Show.

“Watch this space,” is all McCarthy will say regarding future improvements to Ford’s already impressive and expressive Duratec 35.

For him, it all still comes back to simplicity.

“To make something that is very good from a functional standpoint, but is relatively simple,” is the true test – and is validation of the Duratec 35’s development process, McCarthy says.

“You don’t need extra gadgets.”