Detroit Diesel Series 71

Detroit Diesel Series 71

The Detroit Diesel Series 71 is a two-stroke cycle Diesel engine series, available in both inline and V configurations, with the inline models including one, two, three, four and six cylinders, and the V-types including six, eight, 12, 16 and 24 cylinders. The three largest V units used multiple cylinder heads per bank to keep the head size and weight to manageable proportions, the V-12 and V-24 using two and four heads from the inline six cylinder model and the V-16 using four heads from the four cylinder inline model. This feature also assisted in keeping down the overall cost of these large engines by maintaining parts commonality with the smaller models.

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 V-type first appeared in 1957. The 71 in the model series designation refers to the displacement per cylinder in cubic inches (actually 70.93 cu in / 1,162.4 cc). Bore and stroke is the same to all units, at 4.25 x 5.0 inches (107.95 x 127 mm).

All 71 series engines utilize uniflow scavenging, where a gear-driven Roots type blower mounted to the exterior of the engine provides intake air through cored passages in the engine block and ports in the cylinder walls at slightly greater than atmospheric pressure. The engine exhausts through push-rod operated poppet valves in the cylinder head(s), with either two or four valves per cylinder. Unit fuel injection is employed, one injector per cylinder, with no high fuel pressure outside of the injector body. The injectors are cycled from the same camshaft responsible for opening the exhaust valves.

As a two stroke Diesel engine cannot naturally aspirate (draw in) intake air, a blower is necessary to provide sufficient air to scavenge exhaust gasses from the cylinders and support combustion. Later high performance versions were available with turbochargers, and turbochargers with aftercooling, the turbochargers discharging into the Roots blower intake.

Motor Coach Industries MCI-9 bus powered by a rear-mounted 8V-71 Detroit Diesel engine.

The most popular incarnations of the series 71 engine as used for highway vehicle applications included the inline 6-71, the V-block 6V-71 (both widely used in transit buses) and the 8V-71. In addition to motorcoach propulsion, both inline and V types have found extensive usage in trucks, fire apparatus, motor homes, construction and industrial machinery, and military vehicles and equipment. The 71 series 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 inline 6-71 engine, in all of its variations, was also available as a 'pancake engine' (here invariably called either 6L-71 or 6N-71) for horizontal (underfloor) mount applications, such as on larger Crown and Gillig school buses and articulated puller transit buses (such as the Ikarus 286).

Over the years, the 71 series has enjoyed a reputation for dependability and ease of maintenance. Due to their ubiquity and operating characteristics, inline models acquired a variety of nicknames from those who used and serviced them. Most common were "Screaming Jimmy" (Jimmy being trucker slang for GMC trucks) or "Rocky Mountain Humming Bird," which terms referred to the engine's sound at full throttle. Other nicknames include "Green Leaker" and "Driptroit Diesel," referring to the powerplants' factory color and propensity for leaking oil on everything in or near the engine compartment. The v12 has been called the "Buzzin Dozen" due to the higher RPM needed for it to produce power and what sound it makes when the engine brake is on.

71 series variants

Model Displacement Engine configuration Horsepower
1-71 1.2L (71ci) Single cylinder 10
2-71 2.3L (142ci) I-2 68
3-71 3.5L (213ci) I-3 113
4-71 4.7L (284ci) I-4 121
6-71 7.0L (426ci) I-6 190
6V-71 7.0L (426ci) V-6 210
8V-71 9.3L (568ci) V-8 318
12V-71 14.0L (852ci) V-12 450
16V-71 18.6L (1136ci) V-16 480
24V-71 27.9L (1704ci) V-24 1800


Model Codes
T Turbocharged
V V-Block configuration
L or N Low profile

See also


  1. ^ "Diesel Engine Specs". 2007-03-14. Retrieved 2010-12-02. 

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