Boat Engines: Are 6-71 Detroits A Good Choice?

The Detroit 6-71 is a two-stroke diesel engine series, available in both inline and V configurations, manufactured by Detroit Diesel. The 6-71 engine was introduced in 1938 as the initial flagship product of the Detroit Diesel Engine Division of General Motors. The engine was in high demand during World War II and was used in landing craft, ships, tanks, trucks, and earth-moving equipment. The 6-71 engine is known for its reliability and simplicity, and hundreds of thousands of these engines are still in use today.

When considering the 6-71 engine for boat applications, there are several factors to consider. The 6-71 engine is a two-cycle engine, which means it has a different operating system than a four-cycle engine. The 6-71 engine has a longer stroke and smaller bore compared to most four-cycle engines, resulting in higher torque at lower speeds but limiting its top RPM range. The engine is also heavier and has more internal parts compared to some four-cycle engines.

In terms of reliability, the 6-71 engine has a reputation for being dependable, with proper maintenance. It is important to keep the engine speed low to prolong its life. The 6-71 engine is versatile in terms of power ratings and can be run at a broad range of power ratings by making relatively minor changes. However, increasing the injector size to achieve higher power ratings will result in reduced engine life.

The 6-71 engine is also known for its unique sound, as it is a two-stroke diesel with a gear-driven Roots supercharger. This supercharger allows the engine to develop maximum torque and horsepower at the same RPM, creating a distinctive racket that has seduced generations of yachtsmen.

Overall, the Detroit 6-71 engine is a reliable and versatile powerplant that has been used in a variety of applications, including boats. With proper maintenance and operating procedures, the engine can provide long-lasting and efficient performance.

The Detroit 6-71 is a reliable engine

The Detroit 6-71 is a two-stroke diesel engine series, available in both inline and V configurations. The inline six-cylinder 71 series engine was introduced as the initial flagship product of the Detroit Diesel Engine Division of General Motors in 1938.

The engine was in high demand during World War II, with about 57,000 6-71s used on American landing craft and 39,000 used in armour. The 6-71 makes a unique sound because it’s a two-stroke diesel. Unlike the two-stroke engine that most of us know from our experience with outboards, the two-stroke diesel requires a supercharger to fill the cylinder with air via passages in the block and ports in the cylinder’s liner.

The 6-71 is very popular in marine applications, not only as a propulsion engine in small craft but as auxiliary power to drive generators, winches and other heavy shipboard machinery. The engine is also used in trawlers, where they are generally not asked to make high horsepower.

The 6-71 is a good fit for a trawler at low speed. One owner of a trawler with a single 6-71 said: "I wouldn't hesitate to own another boat powered by 6-71s, assuming all was well within them."

The 6-71 is a very durable engine but it burns a lot of fuel relative to its power output and has a nearly non-existent torque curve. They are also not very fuel-efficient when compared to modern four-stroke engines.

The 6-71 is a little different from four-stroke engines. Exhaust noise can be louder if mufflers are not carefully designed. They sound a little different, some like it, some don't.

Hundreds of thousands of the 71 series engines continue to labour on in stationary applications, earth-moving equipment, buses, trucks, ships and boats.

The 6-71 is also easy to work on compared to other diesel engines. One owner said: "Pretty simple engine to work on compared to other diesel engines. End of the day, mine never let me down."

It's a two-stroke diesel engine

The Detroit 6-71 is a two-stroke diesel engine. This means it uses compression ignition in a two-stroke combustion cycle. In compression ignition, air is first compressed and heated; fuel is then injected into the cylinder, causing it to self-ignite. This delivers a power stroke each time the piston rises and falls, without any need for the additional exhaust and induction strokes of the four-stroke cycle.

The two-stroke cycle can be broken down into four stages: intake, compression, ignition, and exhaust. In the Detroit 6-71, these four stages occur in one revolution of the crankshaft, delivering a power stroke with each revolution.

The Detroit 6-71 was introduced in 1938 by the Detroit Diesel Division of General Motors as its premier engine. The engine's name refers to the number of cylinders in line (6) and the displacement of one cylinder in cubic inches (71). The engine was widely used during World War II in landing craft, ships, tanks, trucks, and earth-moving equipment.

The Detroit 6-71 is known for its unique sound, which is due in part to it being a two-stroke diesel. Unlike a conventional gasoline-fuelled two-stroke, the diesel version has a sealed crankcase to contain lubrication oil. The two-stroke cycle of the Detroit 6-71 is as follows:

• Intake: Air is admitted to the cylinder through ports in the cylinder wall. The Detroit 6-71 requires artificial aspiration and uses a mechanically driven blower or a turbo-compressor to charge the cylinder with air.
• Compression: As the piston rises, the air charge is compressed.
• Ignition: Near the top of the piston's travel, fuel is injected, resulting in combustion due to the high pressure and heat in the cylinder. This drives the piston downward.
• Exhaust: As the piston nears the bottom of its stroke, the exhaust port is opened to expel the high-pressure combustion gases. The piston then uncovers the air intake ports in the cylinder wall, and the cycle begins again.

The Detroit 6-71 is known for being a reliable engine, with some users reporting running the engine for tens of thousands of hours without issues. However, it is also known for being loud and prone to leaking oil. The engine is also considered fuel-inefficient compared to other engines, burning a lot of fuel relative to its power output.

Overall, the Detroit 6-71 is a durable and reliable two-stroke diesel engine, but it has some drawbacks in terms of fuel efficiency and noise levels.

It was used in landing craft during World War II

The Detroit Diesel 6-71 engine was used extensively during World War II, powering landing craft, ships, tanks, trucks, and earth-moving equipment. The Gray Marine Motor Company modified the 6-71 engine for marine use, creating the Gray Marine 64HN9/Detroit Diesel 6-71, which was used in Higgins LCVP landing craft. This craft, also known as the Higgins Boat, was considered one of the most important weapons of the war by Dwight D. Eisenhower, thanks to its ability to get right up onto the beach and unload troops directly onto the shore. The craft's engine was a collaboration between Detroit Diesel and Gray Marine, with Detroit Diesel providing the operating engine and Gray Marine adding a transmission, a water-to-water/alcohol heat exchanger, a governor, an air intake with a silencer, and a flywheel assembly.

The 6-71 engine was also used in tanks during the war, including the M4A2 Sherman, the M10 Tank Destroyer, and the British and Canadian Valentine tank. In 1941, GM built 9,000 6-71s, and by 1944, annual production had increased to 62,000 units. During the war years, about 100,000 GMC 6-71 engines were built, serviced, and operated, with the 6-cylinder model being the major production model used by the military. The 6-71's durability and performance in demanding conditions cemented its reputation, leading to its expansion into the marine industry post-war.

It's a good fit for trawlers at low speed

The Detroit Diesel 6-71 is a good fit for trawlers at low speed. The 6-71 is a two-stroke diesel engine series, available in both inline and V configurations, manufactured by Detroit Diesel. The inline six-cylinder 71 series engine was introduced as the initial flagship product of the Detroit Diesel Engine Division of General Motors in 1938.

The 6-71 is an inline six-cylinder diesel engine. The 71 refers to the displacement in cubic inches of each cylinder. 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 horsepower (172 kilowatts).

The 6-71 is a good fit for trawlers at low speed because it has a low rated horsepower and modest power settings. At low rated horsepower and modest power settings, the 6-71 is very close in fuel efficiency to modern four-stroke engines. If run at say 1400 rpm and under 5 gallons per hour each, they can run for a very long time, with 10,000 hours and running perfect not being unusual.

The 6-71 makes a unique sound because it’s a two-stroke diesel. Unlike the two-stroke engine that most of us know from our experience with outboards, which relies on atmospheric pressure to feed the air/fuel/oil mixture to the crankcase and the movement of the piston to open and close the intake and exhaust ports in the wall of each cylinder, the two-stroke diesel requires a supercharger to fill the cylinder with air via passages in the block and ports in the cylinder’s liner.

The 6-71 is a reliable engine. During World War II, about 100,000 6-71s were used on American landing craft, and 39,000 were used in armour. A local captain had a 6-92 that had north of 30,000 total hours on it when he retired 4 or 5 years ago. He averaged around 10,000 hours between rebuilds. Hundreds of thousands of the 71 series engines continue to labour on in stationary applications, earth-moving equipment, buses, trucks, ships and boats.

It's loud

The Detroit Diesel 6-71 is a loud engine. It is a two-stroke diesel engine that requires a supercharger to fill the cylinders with air. This supercharger, along with the high rpm at which the engine operates, contributes to the loudness of the engine.

The loudness of the Detroit Diesel 6-71 is well-known and has been described as a racket and a glorious and addictive racket. The sound of the engine has been likened to a turbine and a subwoofer to the treble clatter of combustion and the valve train. The loud exhaust noise of the engine can be particularly noticeable if mufflers are not carefully designed.

In addition to the loudness of the engine itself, the blower, which is necessary to charge the cylinders with air and assist in scavenging exhaust gases, also contributes to the overall loudness of the Detroit Diesel 6-71. The blower has been described as very noisy.

The Detroit Diesel 6-71's loudness is a defining characteristic of the engine and has even been suggested as a factor in hearing loss for those exposed to it for extended periods. This is supported by comments from users who have experienced hearing the engine in person, with one individual stating that they "don't ever want to own another" due to the noise, and another warning to value your hearing before considering this engine.

Overall, the Detroit Diesel 6-71 is a loud engine, and its loudness is a well-known and defining characteristic that has been both admired and complained about by users.

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