GM's new 4.5L Duramax diesel engine promises a 25% increase in fuel economy while providing 310 hp and 525 lb-ft. The new oil-burning powerplant also needs to pass 50 state emissions while providing the efficiency customers are demanding. GM has already provided some details of the Duramax 4.5L, including that the new diesel is roughly the same size as the General's compact small block V8, which means it can fit in more than just trucks and SUVs. The 4.5-liter also reduces the parts count with integrated aluminum cylinder head exhaust manifolds and an integral cam cover intake manifold. GM talked to Automotive News about new features of the lower half of the 4.5L Duramax, and they're just as extensive as the top.

[Source: Automotive News subs req'd]

Diesels run a higher compression ratio than gasoline engines, so components like crankshafts are built heftier to better-handle the enormous pressures of every day use. GM wants to keep the weight of the 4.5L down, though, because a heavy engine leads to heavier mounts, struts and brakes, which adds tonnage to the truck and saps away performance. To accomplish this, engineers started by casting the crank journals into the engine block, which reduces weight and lowers costs while also adding strength and precision. Because the sides of the bearing journals aren't cast into the wall of the cylinder block, the new crank journal design also improves circulation of air between cylinder banks. Better air flow means reduced pumping losses, which improves efficiency. GM has not used this process before, and may build the design into future gasoline engines.

Other noteworthy features of the 4.5L Duramax include a hollow balance shaft that transfers noise to the rear of the engine and into the thick transmission housing, which mutes engine noise. An aluminum upper oil pan that mounts between the engine block and the lower oil pan also stiffens the engine block by 30%, reducing vibration.The 4.5L Duramax diesel is scheduled to see production in fall of 2009 in the Chevy Silverado and GMC Sierra.

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