New 6.6-liter Duramax Diesel for Chevy Express/GMC Savana Vans

GM recently allowed brief drives in the next-gen meaner, cleaner Duramax diesel engine, albeit in the lighter-duty G-van (Chevy Express/GMC Savana) application. Changes to the new D-max are significant, including revisions to the cylinder block to improve rigidity and reduce noise, an upgrade to 2000-bar (29,000-psi) piezo injectors, and a complete system-hardening to tolerate 20-percent biodiesel mixtures.

Along with the upgrades to the lines, seals, and fittings required for the B20 fuel comes a switch away from post-injection of diesel fuel in the cylinder, in favor of injecting diesel fuel directly into the exhaust in order to purge the soot that collects in the diesel-particulate filter. This eliminates the problem of cylinder-wall wetting that can lead to oil dilution, which is exacerbated by biodiesel's higher boiling point. This approach also works better with the selective catalytic reduction (SCR, urea-injection) NOx catalyst system that will come standard with the Duramax.

Feeding this system is a 5.8-gallon urea tank that is expected to last for an entire oil-change interval, but if the truck is used for extremely heavy towing it may be expended earlier. As fitted to the vans and their chassis-cab applications, the LGH engine produces 250 horsepower and 500 pound-feet of torque. Exact specs for the 3/4-ton pickup application have yet to be cast in nodular grey iron, but they'll be at least as high as the current ratings (365 hp/660 lb-ft). Our unladen test van accelerated briskly and seemed quite responsive to rolling onto the throttle. And fear not, the noise-reducing block won't leave anyone wondering whether you're piloting a diesel.