I read this a while back, in April on car-truck.com:
Cummins just received US Patent #6,216,658 for an "Engine cylinder block with optimized stiffness. " I have yet to track down much information on the next-generation Cummins ISB turbo diesel intended for the next generation Ram. The new diesel is scheduled to debut in model year 2003 when the 3/4 and 1 ton Rams make their debut. The only fact to emerge so far came from one of my Ace Buzz Patrollers whose driven a Ram equipped with the new engine. He reported that it is the quietest truck diesel he has ever heard. He added that even in a garage it sounded like a gasoline engine.
Cummins latest cylinder block patent may explain how this is being achieved. The block has several features built in that enhance structural stiffness, thereby reducing noise emissions. The block includes an upper portion with cylinder bores and a lower portion forming at least a part of a crankcase. At the upper and lower portions of the block, the casing has sculpted wall portions with a curved, undulate shape.
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At a side of the cylinder block, a closed oil cooler cavity is formed. A wall is provided to generally separate the oil cooler cavity from the water jacket defined within the block. An opening is provided in the wall, but the opening is distally located relative to a water pump outlet that provides a flow of coolant into the cavity, thereby improving the flow direction of coolant across the oil cooler. Also, an opposite side of the cylinder block includes a closed tappet cavity to accommodate push rods. The closed tappet cavity is defined by a sculpted tappet cavity wall that is integrally formed with the upper and lower portions of the block, improving block rigidity.
The above-described features have been found to enhance the stiffness of the block, resulting in substantially reduced noise levels. In particular, the noise level emitted from the cylinder block is substantially lower than the noise level emitted from a cylinder block having conventional structural features. Good news for all of you who are tired of scaring your neighbors when you fire up your diesel equipped Ram.