DETROIT -- General Motors plans a series of expensive changes to its Duramax V-8 engine to cope with tough U.S. diesel emission rules taking effect Jan. 1.

GM says reworking the 6.6-liter diesel, which powers heavy-duty versions of the Chevrolet Silverado and GMC Sierra pickups, won't interrupt production. But the modifications are expected to sharply increase the cost of building the engine.

GM will significantly revamp the emissions system of the Duramax, which also is used in full-sized vans and commercial vehicles. GM Powertrain spokeswoman Susan Garavaglia said the diesel will meet the 2007 regulations with:

* A new variable geometry turbocharger.

* Enhanced exhaust gas recirculation.

* Closed crankcase ventilation system.

* Changes to the exhaust system that include an oxidizing catalytic converter to clean NOx emissions and a particulate filter to lower soot.

Diesel particulate filters, first used in Europe in 2005 on Peugeot and Citroen vehicles, will land in America for the first time on diesel versions of the Mercedes-Benz E320 and the Jeep Grand Cherokee coming this fall.

The new Duramax developed to meet the emissions regulation won't be available until Jan. 1.

GM's upgrades won't be cheap. The particulate filter and oxidizing catalytic converter, for example, could add at least $3,000 to the cost of building the truck.

The estimate is based on hardware costs for older diesels that have been retrofitted with filters and related equipment. GM won't confirm the figures.

Demand is strong for GM's diesel trucks. Capacity from the lone Moraine, Ohio, plant that builds the engine is limited to about 180,000 units a year. Because the Duramax has built a reputation for being smooth, quiet and reliable, GM sells out of diesel trucks each year and gets close to sticker prices, which start at about $30,000 and can go as high as $50,000.

GM's technical solutions differ from what sources say Ford Motor Co., Volkswagen and DaimlerChrysler plan for diesel powerplants in the United States. Ford will launch a revamped Power Stroke diesel truck engine in the first quarter of 2007 that uses piezoelectric fuel injectors.