4.5L Duramax LMK

1/2 Ton Diesel Concept for GMC Sierra, Chevrolet Silverado

General Motors engineered the 4.5L Duramax as an alternative to gas engines in the GMC Sierra and Chevrolet Silverado 1500 pickup models. Production was initially projected for the 2010 model year, but the intense collapse of the United States economy created severe financial woes for GM, forcing the project to be scrapped in the wake of the company's 2009 bankruptcy. Rumors have surfaced that General Motors may be interested in rejuvenating the 4.5L Duramax concept, although nothing tangible has been presented to support claims that engine will appear in the near or certain future.

4.5L Duramax Specs


4.5L Duramax LMK, 72 degree V-8


275 cubic inches, 4.5 liters

Compression Ratio:

16.0 : 1


Single variable geometry turbocharger, air-to-air intercooler


29,000 psi high pressure common rail with Piezo injectors


Dual overhead camshaft, 32 valve, 4 valves per cylinder

Emissions Equipment:

Proposed EGR, DOC, SCR, and DPF systems

Peak Horsepower:

Estimated 310 horsepower

Peak Torque:

Estimated 520 lb-ft

The 4.5L Duramax V-8 was designed specifically for the GMC Sierra and Chevrolet Silverado 1500 pickup models, as opposed to the commonality of designing a truck around a selected diesel engine (as has been typical in the 3/4 and 1 ton market when an engine is provided from a third party manufacturer). The unique 72 degree bank angle allows for the narrow engine to fit in virtually any vehicle that could accommodate a small block gas V-8. A compacted graphite iron (CGI) engine block and aluminum cylinder heads would also provide significant weight savings, as the very nature of the diesel engine is readily attributed by its characteristic weight disadvantage. In its preliminary analysis, the 4.5L Duramax was said to provide up to a 25 percent increase in fuel economy over a comparable gas engine when unloaded and a 40 to 70 percent increase in fuel economy in a fully loaded pickup.

The engine was to feature a unique, reversed exhaust/intake configuration that would feed fresh air to the engine from the outer side of the cylinder head while exhaust would exit from the engine valley side of the head directly into a centrally mounted turbocharger. As opposed to routing exhaust through long lengths of tubing before entering the turbine exit, this proposed concept greatly increases the efficiency of waste heat recovery through the turbocharger. The engine therefore did not have a traditional intake manifold system.

Unlike other Duramax models, the 4.5L was designed without contribution from Isuzu, whom, through a joint venture, contributed significantly to the development of the 6.6L Duramax. The proposed engine would have met tier 2 Bin 5 emissions requirements, making it 50 state legal without the use of selective catalytic reduction (SCR).