For the 2010 model year, General Motors is launching a brand-new 4.5L diesel V-8 engine. The Duramax 4500 is a unique new design specifically developed to fit within the same package space as the company's half-century-old, small-block V-8.  

As an overhead valve, cam-in-block design, the gasoline fueled small-block is a remarkably compact design that's used in many GM truck and passenger car platforms. Designing a modern diesel V-8 to fit within that limited envelope proved a major challenge for GM engine designers who devised some innovative packaging solutions.

As with virtually all modern automotive diesels, the new Duramax is turbocharged and equipped with common rail fuel injection. But unlike the small block and even the larger 6.6L Duramax that GM installs in heavy-duty trucks, the new diesel has dual overhead cam-shafts and four valves per cylinder. Placing the camshafts on top of the cylinder heads inevitably results in a wider design as hardware is stacked on top of the banks.

To compensate for the additional width, the angle between the two cylinder banks has been reduced from the typical 90-degrees for a V-8 to 72 degrees. The other major change to reduce the package size was achieved by reversing the normal flow through the cylinder heads.  

On V-type engines, the intake plenum is typically placed in the valley between the two banks and feeds intake ports on the in-board sides of the cylinder heads. The exhaust manifolds are then mounted on the outboard side of the cylinder heads.

Turbocharged engines rely on the exhaust gas flow to spin up a turbine, which drives a compressor and pushes more air into the intake plenum to provide boost and more power. If the length of the exhaust tubes is too long, it takes longer for the turbine to spin up and the perceived responsiveness when the driver wishes to accelerate is reduced, a phenomenon known as turbo lag. V-type engines often use twin turbochargers (one per bank) in order to keep the exhaust path short and improve responsiveness.

A twin turbo layout also increases the package envelope size. To overcome this, the GM designers moved the exhaust ports to the in-board side of the cylinder heads and mounted the turbocharger in the valley between the banks. This allows for very short exhaust gas runs to the turbocharger. Engine acceleration response is also aided by the use of a variable intake geometry turbocharger.

Getting air from the turbocharger into the engine is handled by intake manifolds mounted above the intake valves on top of the cylinder heads. This leaves the outside of the engine free of appendages. Engines are typically installed from below on assembly lines and the clear sides of this engine allow it to fit between the frame rails.  

The cylinder heads and integrated intake manifolds are made from aluminum, while the cylinder block is cast from compacted graphite iron (CGI). CGI is stronger than conventional grey iron that is used for engine blocks, requiring less material and improving the rigidity of the block. The integration of components, such as the manifolds, has allowed GM to reduce the total part count by about 70 pieces compared to a conventional design.

Fuel delivery to the new engine is handled by a high pressure common rail fuel injection system. The common rail system operates at 29,000psi and the injectors are able to provide up to five pulses per ignition cycle.

The exhaust aftertreatment system consists of a diesel particulate filter and selective catalytic reduction (SCR) system. The SCR system injects a urea solution into the exhaust stream to convert NOx emissions to water and nitrogen. This will be the first GM diesel application of SCR.

The advanced fuel injection and aftertreatment systems will allow the new Duramax to achieve a 13 percent reduction in CO2 emissions and greater than 90 percent reductions in particulate and NOx emissions.

Output of this new 4.5L engine should be at least 310hp with 520Nm of torque. The diesel V-8 will provide a 25 percent reduction in fuel consumption compared to similarly powerful gasoline engines. The first applications of the Duramax 4500 will be in the Chevrolet Silverado and GMC Sierra light-duty pickup trucks for the 2010 model year. The HUMMER H2 is also expected to receive the diesel.

MAY 2008