Gray Marine 6-71 Diesel Engine

The 6-71 Gray Marine Diesel Engine is a marine diesel engine, a marinized version of the General Motors Detroit Diesel 6-71 engine produced by the Gray Marine Motor Company. It was used in landing craft during World War II and is used today in private boats and training facilities.

The 6-71 is a six cylinder engine, and is "inline" or with all cylinders arranged in a straight line. This type of engine is commonly referred to as an "inline six" or an "I-6." The 71 refers to the displacement per cylinder which is 71 cubic inches. The firing order of the engine, or the order combustion occurs in successive cylinder, is 1-5-3-6-2-4. The engine's compression ratio is 18.7:1 with a 4.250 inch bore and a 5.00 inch stroke. The engine weighs 2,185 lb (991 kg) and is 54 inches long, 29 inches wide and 41 inches tall. At 2,100 revolutions per minute the engine is capable of producing 230 horse power (172 kilowatts). V-type versions of the 71 series would not be developed until 1957.

The 6-71 is a two stroke diesel engine. As the engine will not naturally aspirate, air is provided to the engine via a roots-type supercharger. However, on the 6-71T models, both a turbocharger and a supercharger are utilized. Fuel is provided by Unit Injectors, one per cylinder. The amount of fuel injected into the engine is controlled by the engine's governor. The engine cooling is via liquid in a water jacket. In a boat, external cool water is pumped through the boat and passed through a heat exchanger mounted on or nearby the engine in a "double loop" configuration.

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