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testing, and running many of the same validation tests used on the heavy-duty 6.6-liter Duramax V8. "All told," claims Yackley, "that's equivalent to about 2.5-million customer miles before the frst North American-spec engine ever came down the assembly line." The 2.8-liter Duramax features a cast-iron block topped by an aluminum twin-cam head, forged steel crankshaft and connecting rods, and aluminum pistons. Bore and stroke is undersquare at 94 x 100 mm, and scrapers are used on the valve seats to keep every- thing clean. To keep noise and NOx emissions under control, the 2.8-liter four runs a 16.5:1 compression ratio. Each of the four cylinders is fed by a high-pressure common rail fuel system, and the engine uses three injections— pre, pilot and post—per cylinder. Oil jets cool the underside of the pistons, while the oiling circuit also features a dedicated feed for the Honeywell variable nozzle turbocharger that is designed to speed and improve lubrication of the turbine's bearings. Maximum boost is 35-40 lb./in. 2 , and 90% of maximum torque is available from 1,400-2,800 rpm. In addition to the multiple injec- tions and slightly subdued compres- sion ratio, NVH reduction required dedicated strategies. These include a pair of counter-rotating balance shafts mounted just below the crankshaft, a damped steel oil pan and timing cover, plus a damped panel located below the engine cover that runs along the top of the cam cover. In addition, there is a centrifugal pendulum vibration absorber located within the torque converter of the six-speed Hydra- Matic 6L50 automatic transmission to reduce both noise and vibration. Its secondary spring masses vibrate in a direction opposite to that followed by the engine's torsional vibrations, and is the frst use of this technology in a GM vehicle or in the mid-size truck segment. Not surprisingly, the intake manifold is plastic, which not helps to reduce noise, but provides smooth intake runners and integrates a number of parts into a single assembly. AD&P; > December 2015 > FEATURE > Diminutive Duramax Diesel > Christopher A. Sawyer 42