DETROIT — General Motors announced on March 9 the availability of the Duramax 6600 turbodiesel engine in the 2006 Chevrolet Express and GMC Savana G2500 and G3500 series commercial models. The latest version of the 6.6L V-8 Duramax turbodiesel delivers 250 horsepower and 460 lb-ft of torque. It is teamed with GM’s Hydra-Matic 4L85-E electronically controlled four-speed automatic transmission, which is specially tuned for diesel-engine compatibility. Preliminary testing shows composite fuel economy of 20.2 mpg—a 35 percent improvement over the 15 mpg of the gasoline-fueled 5.3L versions. The Duramax 6600 also is compatible with biodiesel fuel. The 2006 version of the Duramax engine features a strengthened iron cylinder block and revised piston design which reduces the compression ratio (to 16.8:1 from 17.5:1). The lower compression reduces the “clattering” sound of the engine at idle, while also helping to improve overall smoothness during driving. The lower compression also helps reduce NOx emissions.