Although the program is “on the shelf,” General Motors Co. Vice Chairman Tom Stephens says the auto maker’s Duramax 4.5L V-8 turbodiesel is ready when needed.

“The program is essentially complete and could be implemented whenever we choose to do that,” GM’s vice chairman-product development tells Ward’s in a phone interview.

The Duramax diesel was expected in GM’s ’10 light-duty fullsize pickup trucks, the Chevrolet Silverado and GMC Sierra, and possibly future cross/utility and SUVs.

But the auto maker’s misfortunes, culminating in a June 1 bankruptcy filing, caused it to cancel the mill’s spring introduction. Another hurdle is declining gas prices, making fuel-saving diesels less alluring for many consumers.

Developed over nearly four years and due to be built at GM’s Tonawanda, NY, plant, the engine’s design defies conventional diesel technology with reverse flow of air and exhaust gases entering and exiting the cylinder heads.

Exhaust gases exit toward the center of the engine directly into the turbocharger, which is located in the “V” between the heads. Placing the forced induction system between the cylinder banks is a cutting-edge design that saves weight and space and improves performance and emissions.

Stephens says the light-duty diesel is among several potential technologies ready on the shelf for volume applications. “I could pull any one off and put it into production very quickly, because they’ve already been concepted, designed, developed. All I’d have to do is pull them out and integrate them into a vehicle and then validate the vehicle.”

GM, which already sells a 6.6L V-8 Duramax turbodiesel for its heavy-duty pickups, is one of several auto makers canceling plans to introduce their first or additional diesel mills, including Toyota Motor Corp., which was to bring a diesel in 2010 for its Tundra fullsize pickup truck and Sequoia large SUV.

On the passenger-car side, Nissan Motor Co. Ltd. has delayed a diesel engine for the Maxima sedan, and Honda Motor Co. Ltd. has canceled the Acura TSX sedan diesel.

Another GM engine with an uncertain future is the gasoline Ecotec 2.0L turbocharged 4-cyl., with direct injection and variable valve timing.

The I-4 currently powers the Pontiac Solstice/Saturn Sky roadsters, as well as the Chevy Cobalt. But GM is shutting down Pontiac and attempting to sell the Saturn brand, while the Cobalt soon will be phased out.

Stephens won’t say what is to become of the 2.0L Ecotec but bristles at the notion GM is behind the curve at a time when many OEMs are bridging turbocharging and direct injection.

“GM was the first manufacturer to do that,” Stephens says. “Don’t count (the Ecotec) out. Direct injection, variable valve timing, as well as turbocharging, will be used on vehicles ongoing at GM. There’s absolutely zero doubt about that.”

GM has announced plans for 18 models with direct-injection gasoline engines by next year, including the GMC Terrain CUV, whose 4-cyl. and V-6 mills both will feature direct injection.

But the 2.0L Ecotec is GM’s only DI turbocharged gasoline engine, for now. Other GM models with direct injection include the ’10 Buick LaCrosse, Chevy Camaro and Equinox and Cadillac SRX.

Meanwhile, as it did with the Chevy Volt, General Motors will aggressively promote its advancements with homogeneous charge compression ignition (HCCI) engine technology.

Stephens says GM will keep the media and buying public updated on HCCI, which marries the best features of gasoline and diesel engines. HCCI allows an engine to optimize combustion by employing spark ignition in the cylinder during certain driving conditions and compression ignition during others.

The technology reduces the amount of heat lost as energy during combustion and is expected to improve fuel economy some 15% over conventional spark-ignition powertrains.

“We have not and don’t intend to put a production date on HCCI,” he says, adding GM’s last major breakthrough with the technology – and an industry-first – was showing HCCI operation at idle.

“So we’re making part of the speed load map, where HCCI can be enabled, we’re making it larger and larger and larger,” Stephens says. “Once it gets large enough, that’s where we’ll probably make the call to put (HCCI engines) into production.”

Stephens classifies GM’s development status on HCCI, which he calls “the holy grail” of combustion systems, as being “further along than we ever thought we could be at this point.”

cschweinsberg@wardsauto.com