General Motors announced last week 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 6.6-liter V-8 Duramax turbodiesel delivers 250 horsepower and a robust 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% improvement over the 15 mpg of the gasoline-fueled 5.3-liter 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.