Duramax diesels rev up GM truck sales

Diesel comparisons
GM/Isuzu Duramax turbocharged diesel V-8

  • Vehicles: Chevrolet SilveradoHD/GMC Sierra HD

  • Hp: 300

  • Torque: 520 lbs.-ft.

  • Fuel system: Common rail
    with direct injection

  • Displacement: 6.6 liters

  • Block: Cast iron

  • Heads: Aluminum, 4 valves per cylinder

    Ford/Navistar Power Stroke turbocharged diesel V-8

  • Vehicles: Ford Super Duty pickup and Excursion
  • Hp: 235

  • Torque: 500 lbs.-ft.

  • Fuel system: Hydraulic-electric unit direct injection

  • Displacement: 7.3 liters

  • Block: Cast iron

  • Heads: Cast iron, 2 valves
    per cylinder

    Dodge/Cummins turbocharged diesel inline 6-cylinder

  • Vehicles: Dodge Ram 2500, 3500

  • Hp: 235;
    optional engine: 245

  • Torque: 450 lbs.-ft.;

  • optional engine: 505

  • Fuel system: Electronic
    high-pressure direct injection

  • Displacement: 5.9 liters

  • Block: Cast iron

  • Head: Cast iron, 2 valves
    per cylinder

    Source: Automotive News

  • General Motors lost sales leadership of full-sized trucks to Ford Motor Co. in 1996 but has a chance of regaining the title in 2001.

    Through September, Ford’s F series had a slim 4,000-unit lead over the Chevrolet Silverado and GMC Sierra.

    GM believes the Duramax diesel engine, developed with Isuzu Motors Ltd., will help it capture at least 25 percent of the diesel truck market. Sales of the Duramax have tripled those of GM’s previous-generation diesel engine. Isuzu does not sell a version of the engine in its vehicles.

    It hasn’t hurt that GM launched the Duramax during a sales boom for heavy-duty trucks. Diesels deliver fuel economy gains of as much as 25 percent over gasoline-powered engines, and they haul heavier loads.

    Sales of heavy-duty diesel-powered pickups grew 6.34 percent from 1999 to 2000 to about 300,000, according to Polk Automotive Intelligence, which tracks registrations.

    If sales at one Texas Chevrolet dealership are any indication, GM might be able to reach its sales goal.

    Before GM introduced the Duramax, Frank Parra Chevrolet in Irving, Texas, sold about 10 Chevrolet diesel trucks annually. With the Duramax, sales of diesel-powered Chevy trucks are averaging 10 per month.

    “Demand is fairly strong. We are starting to find our loyal Chevy owners coming back. They’ve been waiting to buy a diesel again,” said Butch Armstrong, Internet sales manager for the dealership. “As consumer confidence returns, we’ll be right there with Ford. And in the long run, I expect it to outdo Ford.”

    Long road back

    GM damaged the reputation of the diesel 20 years ago when it rushed poorly engineered engines to the market in response to fuel shortages.

    That history weighed heavily on the minds of the GM and Isuzu engineers who designed the Duramax. They knew recalls would hurt the engine. Using four-valve aluminum cylinder heads on an iron block along with common rail direct-injection fuel system complicated matters .

    James Kerekes, chief engineer for GM’s diesel engines, said there was no room for error with the new diesels. He credits GM’s tie-in with Isuzu for the trouble-free launch.

    “It was our intention all along to bury those ghosts from the past. We looked around heavy-duty pickups, the market we were after in North America, at who had the best diesel. We think Ford/Navistar did, and we benchmarked it. We measured it. We drove it. Then we set our expectations higher because we knew Ford wouldn’t sit still,” said Kerekes.

    Ford won’t comment on its plans for diesels.

    “Amongst industry people, I think GM definitely buried the reputation of bad diesels. But amongst consumers, most think diesels as smoky, noisy Oldsmobile engines. Until someone like Volkswagen, GM or Ford brings a European diesel to the U.S., those perceptions are not going to change,” said Eric Fedewa, director of global powertrain forecasting for CSM Worldwide, a consulting company in Northville, Mich.

    High-tech fuel system

    Of the three diesel engines available — the Cummins inline-six cylinder used in the Dodge Ram, the Power Stroke V-8 built by International Truck and Engine Corp. for the Ford F series and the Duramax — the GM engine is the quietest, smoothest and most powerful.

    The key is pilot injection. A small blast of fuel is shot into the cylinder just before the pistons reach top dead center, starting a pre-combustion burn, which enables the main injection of fuel to ignite more evenly.

    At GM’s Powertrain’s test facility in Romulus, Mich., Kerekes demonstrated pilot injection. With a Durmax engine on a test stand running at about 1,400 rpm, an operator switched off the pilot injection, and the engine became much louder, almost as if it had a few loose rod bolts.

    The common rail, direct-injection fuel system is supplied by Bosch and shoots fuel at high pressure and in a fine mist into each cylinder. Duramax is the only pickup engine that uses the system, though it is common on European diesel engines.

    Isuzu engineers in Japan designed the layout of the Duramax, and, Kerekes says, taught their GM counterparts lessons about paying attention to details.

    “It really was a team effort. There were a lot of video conferences — three or four a week. We kind of turned that 13-hour time change into an advantage during the development program,” Kerekes said.

    “We would work on an issue here and then have a video or telephone conference at the end of our working day. And then in Japan they would work on it all night because it was the beginning of their day. Then we’d have another conference in the morning. It was like a 24-hour-a-day activity, and it worked out well,” he said.

    The project was completed in 37 months, down from the usual 60 months it takes to bring an engine to market. GM engineers selected most of the materials, such as aluminum for the heads, which run about 200 degrees Fahrenheit cooler than cast iron. GM engineers calibrated the fuel system and wrote the software for the Allison five-speed automatic transmission.

    A passion for diesels

    GM’s diesel strategy for cars still is evolving, but it likely won’t include the Duramax engine.

    Jack Blanchard, GM’s assistant chief engineer for diesel engineering, said the Duramax could be made into a V-6, possibly for use in light-duty trucks and mid-sized sport-utilities. But Kerekes said diesels for GM cars likely would come from GM’s alliance partners or its European operations.

    Said Kerekes: “What I’ve learned in working with diesels in the last four or five years is that there is a real passion for diesels.

    “There are two kinds of people: those who like diesels and those who don’t like diesels. When they like them, they are strong about their trucks.”

    You can reach Richard Truett at rtruett@crain.com

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