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General Motors sees a future for engines with overhead valves, a technology most automakers have abandoned in favor of overhead camshafts.

GM will introduce a new family of overhead-valve (OHV) V-6s beginning with a 3.5-liter engine in the 2004 Chevrolet Malibu and plans to keep other OHV engines in its fleet for years.

Few foreign manufacturers offer OHV car or light-truck engines in the U.S., and Ford and Chrysler have reduced their OHV offerings in favor of overhead-cam (OHC) designs.

By contrast, overhead-valve engines will account for the majority of GM's future engine production, Ned McClurg, vice president of engineering for GM Powertrain, said at a recent stop in Chicago.

"We're making major investments in them. A case can be made that overhead-valve engines produce more power per mass and more power per physical space," McClurg said.

OHV engines are widely considered low-tech compared with overhead-cam engines and incapable of meeting more stringent emissions requirements facing automakers, but McClurg disputes such claims.

"We are doing just fine with overhead-valve engines, whether you're looking at quality, performance, fuel economy or customer satisfaction," he says. "Others say you can't do that with overhead-valve engines. The reality is we do it.

"I know we're arguing against the tide, but we're going to surprise the industry with innovation," he said. "We're not going to give away anything on noise, emissions, quality or reliability."

Art Spinella, general manager of CNW Marketing/Research, a Bandon, Ore., firm that studies consumer buying decisions for the auto industry, says most buyers could care less what is under the hood.

"The vast majority, and I mean 85 percent or more, don't care. There's a certain percentage who do, but they already drive European or Japanese vehicles," Spinella said.

"As long as it starts when it's 30 degrees in Chicago, it doesn't matter if it's overhead valve, overhead cam, hybrid or a fuel cell. They don't care if there are hamsters under the hood as long as it gets them to the office."

In the 1980s, OHV engines couldn't match the performance or fuel economy of OHC engines, "but today the engine configuration or design really is not an issue," he added.

OHV engines have a single camshaft in the engine block that operates pushrods that open and close the valves. With OHC engines, camshafts are mounted in the cylinder heads, closer to the valves, where they can open and close the valves faster and allow the engine to operate at higher speeds.

GM says cost is a major factor favoring OHV engines because they have fewer parts and are cheaper to manufacture than OHC engines, most of which have two camshafts per cylinder head and four valves per cylinder (instead of two on the OHV).

"When you have four camshafts instead of one, the difference is pretty straightforward," McClurg said, though he wouldn't specify the cost differences.

GM estimates its OHV truck V-8s cost $700 to $800 less to produce than Ford's OHC V-8s, and McClurg said of Ford's engines, "Basically, they lose on both performance and fuel economy."

GM's V-8s have more horsepower, but Ford's have greater torque. According to the federal EPA, GM's 4.8- and 5.3-liter OHV V-8s match Ford's 4.6- and 5.4-liter OHC V-8s in fuel economy. In combined city/highway driving, the smaller engines get 17 m.p.g. and the larger versions get 16.

Spinella says that in practice he has found GM's engines more efficient. CNW maintains a fleet of vehicles for consumer research clinics, and Spinella says the OHV V-8s in GM's full-size SUVs "get much better real-world mileage" than the OHC V-6 in the midsize Ford Explorer.

Dave Szczupak, Ford's vice president of powertrain operations, argues that Ford's overhead-cam engines are smoother, quieter and more efficient without a cost penalty.

"We don't believe there's a financial disadvantage to our engines," Szczupak said, adding that any additional cost from the greater complexity of overhead-cam designs is offset by production efficiencies.

Ford builds OHC V-8s for trucks and cars and a V-10 truck engine from the same design, adding up to 1.3 million engines per year. Ford also is adopting a flexible manufacturing system it says will allow revising engine production at lower cost in the future.

"With the manufacturing efficiencies we will realize, we will produce our engines at very similar cost [compared with GM]," Szczupak said.

As far as GM's claims of superior performance, Ford will introduce a revamped 5.4-liter engine in the spring with 300 horsepower and 365 foot-pounds of torque, topping GM's engine on both counts.

GM's faith in OHV engines also stems from its commitment to displacement-on-demand, technology that disables half of an engine's cylinders once a car reaches cruising speed. DOD is easier to incorporate into OHV engines and GM predicts it will improve fuel economy 8 percent.

GM's DOD system debuts in a 5.3-liter truck V-8 in 2004 and will become available on a 3.5-liter V-6 in the Malibu the following year.

OHV engines also tend to be more compact than OHC engines, making them easier to fit into a variety of vehicles.

McClurg says GM is working on technical improvements, such as three valves per cylinder and electronic throttle control, that will help extend the life of OHV engines.

To reduce development costs, McClurg says most future engines and transmissions will have "high bandwidth architecture," using an approach similar to Ford's in which one design spawns multiple variants.

For example, in addition to the 3.5-liter engine, the new OHV V-6 family will include 3.1- and 3.9-liter versions. At full production GM will build up to 5,000 per day.

GM will derive the new OHV V-6s from the design for the 3.1- and 3.4-liter V-6s used in several front-wheel-drive cars and minivans. Those engines were derivatives of the 2.8-liter V-6 that debuted in the 1980 Chevrolet Citation and similar cars.

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