Detroit Diesel 8V71T Specifications
| Engine Model: Detroit Diesel 8V71T |
| Engine Type: 2-stroke 8-cylinder 90-deg V-block turbocharged liquid-cooled diesel |
| Total Displacement: 568 cu.in (9.3 L) |
| Rated Engine Power: 375-450 Hp (280-336 kW) at 2300 rpm |
| Fuel System Type: Mechanical unit injection (MUI) |
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The Detroit Diesel 8V71T is a turbocharged,
90-degree V-configuration, 8-cylinder two-stroke diesel engine within
the legendary Series 71 family. Introduced as a higher-output evolution
of the naturally aspirated 8V71, the 8V71T incorporated turbocharging
and a roots-type scavenging blower to increase power density for marine,
industrial, and off-highway applications. The engine retained the
fundamental architecture of the Series 71 line—a two-stroke cycle with
unit injectors and a valveless cylinder design where ports in the
cylinder liner controlled intake and exhaust timing.
The 8V71T utilized a 4.25 in bore and 5.00 in stroke, displacing 568
cu.in. Its construction featured a cast iron block with individual
cylinder heads per cylinder, a cast iron crankshaft, and a unit fuel
injection system driven by the engine’s camshaft. The engine’s power
output ranged from 375 to over 450 hp depending on application and
governor calibration, with torque outputs exceeding 1,000 lb-ft. The
8V71T served extensively in transit buses, fire apparatus, heavy trucks,
marine vessels, and industrial equipment, earning a reputation for
durability and a distinctive two-stroke exhaust note.
Engine Type: 2-stroke, 90° V8, water-cooled turbocharged diesel.
Displacement: 568 cu.in (9.3 L).
Bore: 4.25 in (108.0 mm).
Stroke: 5.00 in (127.0 mm).
Maximum Power: 280-336 kW (375-450 hp) at 2,100-2,300 rpm.
Maximum Torque: 1,356-1,508 Nm (1,000-1,112 lb-ft) at 1,200-1,600 rpm.
Maximum Governed Speed: 2,300 rpm (highway); 2,500 rpm (industrial and
marine).
Idle Speed: 525-575 rpm.
Firing Order Interval: 90° crankshaft rotation between firing events.
Compression Ratio: 17.0:1.
Firing Order: 1L-3R-3L-5R-5L-8R-8L-2R-2L-4R-4L-1R.
Cylinder Arrangement: 90° V-angle.
Aspiration: Single turbocharger with roots-type scavenging blower in
series; blower provides scavenging air at idle and low load;
turbocharger supplements airflow at higher engine speeds.
The cylinder block is constructed from high-strength gray cast iron with
a 90-degree V configuration. The block is a single casting incorporating
the cylinder banks, crankcase, and camshaft galleries. Cylinder bores
are machined directly into the block without replaceable liners, though
a wet-sleeve design was employed on certain variants where removable
cylinder liners were specified. The block features a deep-skirt design
extending below the crankshaft centerline.
Seven main bearings support the cast iron crankshaft, with bearing caps
secured by vertical bolts. The crankshaft is of forged steel
construction in higher-output marine and industrial variants. The block
incorporates an integral air box on each bank, which serves as the
distribution manifold for scavenging air entering the cylinder ports.
Accessory mounting pads are cast into the block for the fuel pump, air
compressor, and other engine-driven equipment.
The 8V71T utilizes individual cylinder heads for each cylinder, rather
than a single head per bank. Each head is a cast iron casting containing
the unit injector mounting bore, the pre-combustion chamber (in earlier
naturally aspirated variants; turbocharged versions used direct
injection), and the fuel injector control mechanism.
The valveless design of the Series 71 engine eliminates conventional
intake and exhaust valves. Instead, the cylinder liner contains intake
ports at the lower portion of the bore and exhaust ports at the upper
portion. The movement of the piston uncovers these ports to control gas
flow. This ported cylinder design is characteristic of two-stroke
Detroit Diesel engines.
Number of Cylinder Heads: 8 (individual per cylinder). Cylinder Head
Material: Cast iron. Intake Ports: Circumferential ports in lower
cylinder liner, uncovered by piston at bottom dead center. Exhaust
Ports: Circumferential ports in upper cylinder liner, uncovered by
piston near bottom dead center. Injection System: Unit injector mounted
in each cylinder head, driven by rocker arm from camshaft.
The fuel system employs a unit injector (UI) design where each cylinder
has a dedicated injection pump and nozzle combined into a single
assembly. The unit injectors are mounted vertically in each cylinder
head and actuated by a rocker arm driven by the camshaft. Fuel is
supplied from a chassis-mounted fuel tank through a primary filter to a
gear-type transfer pump mounted on the engine.
The transfer pump delivers fuel to the secondary fuel filters and then
to the unit injectors. Excess fuel recirculates to the tank, providing
cooling to the injectors. The governor is mounted on the fuel pump and
controls engine speed by regulating fuel delivery. Turbocharged variants
incorporate a fuel-air ratio control mechanism to limit fuel delivery
under boost until adequate airflow is available.
Injectors: Unit injector; each injector incorporates its own plunger,
barrel, and spray nozzle; injection pressure determined by cam profile.
Fuel Filtration: Primary spin-on filter with water separator; secondary
spin-on filter (2 micron) mounted on engine. Fuel Transfer Pump
Pressure: 345-483 kPa (50-70 psi). Fuel Specification: ASTM D975 No. 2
diesel; No. 1 diesel for cold-weather operation.
The lubrication system utilizes a gear-type oil pump mounted within the
oil pan and driven by the camshaft gear train. The pump draws oil
through a strainer screen from the sump and delivers it to a full-flow
spin-on oil filter mounted on the engine. An integral oil cooler, using
engine coolant, maintains oil temperature. The system incorporates a
pressure relief valve calibrated to maintain stable pressure.
Main galleries distribute oil to the crankshaft main bearings,
connecting rod bearings, camshaft bearings, rocker arms, and unit
injector control mechanisms. The turbocharger receives oil through a
dedicated supply line with a restricted orifice. The oil pan capacity
varies by application and chassis configuration.
Oil Pump Type: Gear-type, camshaft-driven.
Oil Pressure (operating, governed speed): 275-415 kPa (40-60 psi).
Oil Pressure (hot idle): 35 kPa (5 psi) minimum.
Oil Capacity (with filter, standard sump): 26.5-34.0 L (7-9 gal).
Oil Specification: API CD, CE, CF; SAE 40, SAE 30.
The cooling system employs a belt-driven centrifugal water pump mounted
to the front of the engine. Coolant flows from the radiator through the
pump, then through the cylinder block water jacket, upward into the
cylinder heads, and returns to the radiator through a thermostat
housing. A wax-pellet thermostat maintains operating temperature.
The system incorporates a cross-flow radiator with a pressure-type
filler cap rated at 50-70 kPa (7-10 psi) for most applications. A
separate coolant circuit serves the oil cooler and the turbocharger
bearing housing on turbocharged variants. The coolant capacity varies
with radiator size and application.
Water Pump Type: Belt-driven centrifugal pump with cast iron housing.
Coolant Capacity (engine and radiator): 30-38 L (8-10 gal) depending on
application.
Thermostat Opening Temperature: 71-77 °C (160-170 °F).
Thermostat Fully Open Temperature: 85-88 °C (185-190 °F).
Coolant Specification: Ethylene-glycol based with supplemental coolant
additives (SCA).
| Intake and Scavenging System |
The 8V71T employs a combination of a roots-type scavenging blower and a
single turbocharger. The roots blower, mounted on the engine and driven
by gear train from the crankshaft, provides positive airflow for
scavenging at idle and low engine speeds. As engine speed increases, the
turbocharger supplies compressed air to the blower inlet, increasing
manifold pressure.
Scavenging air passes from the blower through the air box in each
cylinder bank, then through ports in the cylinder liner when the piston
uncovers them near bottom dead center. This system purges exhaust gases
and fills the cylinder with fresh air for the next combustion cycle.
12 V or 24 V negative-ground electrical architecture depending on
vehicle specification. Starter motor is a heavy-duty gear-reduction or
direct-drive unit mounted to the flywheel housing. Alternator output
ranges from 50 A to 100 A. Starting aid includes a glow plug or intake
air heater in cold-weather configurations.
Turbocharger System: The turbocharger is a single, water-cooled,
wastegate-equipped unit mounted to the exhaust manifold. The turbine
housing is sized to provide adequate airflow while minimizing back
pressure. Maximum boost pressure is regulated to 70-90 kPa (10-13 psi)
depending on application and calibration.
Exhaust System: Cast iron exhaust manifolds on each cylinder bank merge
into a single crossover pipe feeding the turbocharger turbine inlet. The
exhaust system includes expansion joints to accommodate thermal
expansion. A muffler and exhaust stack or tailpipe are fitted according
to vehicle configuration.
Governor System: The engine is equipped with a Woodward or equivalent
mechanical governor mounted on the fuel pump. The governor controls
engine speed by regulating the position of the fuel racks, which in turn
controls fuel delivery from the unit injectors. High-speed and low-speed
limiting springs maintain governed speed settings. Industrial and marine
variants incorporate isochronous governors for constant-speed operation.
Length (front of accessory drive to rear of flywheel housing):
1,270-1,575 mm (50-62 in) depending on accessory configuration.
Width (overall, across cylinder heads): 890-1,015 mm (35-40 in).
Height (from oil pan rail to top of air intake): 1,145-1,345 mm (45-53
in).
Dry Weight (complete engine, without transmission): 1,045-1,130 kg
(2,300-2,495 lb) depending on accessory configuration and turbocharger
installation.
Engine Oil: API CD, CE, CF; SAE 40 above 0C (32F); SAE 30 for cold
climates.
Oil Change Interval: 250-500 hours (industrial/marine).
Oil Change Interval: 8,000-16,000 km (5,000-10,000 mi) for on-highway
applications.
Oil Filter Replacement: Every oil change; two spin-on filters standard.
Coolant Capacity: 30-38 L (8-10 gal).
Coolant Change Interval: 2,000 hours or 24 months.
Fuel Filter Replacement: 500 hours (industrial); 16,000 km (10,000 mi)
(on-highway).
Air Filter Replacement: 500 hours or as indicated by restriction gauge.
Valve and Injector Adjustment: Inspect and adjust every 500-1,000 hours.
Injector Timing: 1.460 in (37.1 mm) injector plunger travel for standard
calibration.
Idle Speed: 525-575 rpm.
Governed Speed (highway): 2,100-2,300 rpm.
Cylinder Head Bolts: 225-235 Nm (165-175 lb-ft)
Main Bearing Cap Bolts (standard): 400-475 Nm (295-350 lb-ft)
Connecting Rod Bolts (one-piece rod): 108-115 Nm (80-85 lb-ft)
Connecting Rod Bolts (two-piece rod, cap screws): 60-70 Nm (45-50 lb-ft)
Flywheel Housing Bolts (to block): 95-110 Nm (70-80 lb-ft)
Flywheel Bolts: 160-190 Nm (120-140 lb-ft)
Rocker Arm Bracket Bolts: 95-110 Nm (70-80 lb-ft)
Fuel Injector Clamp Bolts: 40-50 Nm (30-37 lb-ft)
Injector Rocker Arm Adjusting Screw Locknut: 25-30 Nm (18-22 lb-ft)
Intake Manifold (air box cover) Bolts: 40-50 Nm (30-37 lb-ft)
Exhaust Manifold Bolts: 60-70 Nm (45-50 lb-ft)
Turbocharger to Exhaust Manifold Bolts: 60-70 Nm (45-50 lb-ft)
Oil Pan Bolts (to block): 40-50 Nm (30-37 lb-ft)
Water Pump Mounting Bolts: 40-50 Nm (30-37 lb-ft)
Thermostat Housing Bolts: 40-50 Nm (30-37 lb-ft)
Engine Mount Bracket to Block: 130-160 Nm (95-120 lb-ft)
Crankshaft Pulley / Damper Bolt: 600-800 Nm (440-590 lb-ft)
Camshaft Drive Gear Bolts: 160-190 Nm (120-140 lb-ft)
On-Highway Trucks: Heavy-duty trucks and tractor-trailer configurations;
popular in the 1960s through 1980s for over-the-road and vocational
applications.
Transit Buses: City transit buses and intercity coaches; widely used by
transit agencies for two-stroke reliability and sound signature.
Fire Apparatus: Fire trucks and crash rescue vehicles requiring high
power density and rapid throttle response.
Marine Propulsion: Commercial fishing vessels, workboats, and
recreational craft; both inboard and generator set configurations.
Industrial Power: Generator sets, pumping stations, construction
equipment, mining machinery, and oilfield equipment.
Motor Coaches: Luxury touring buses and charter coaches; the 8V71T was a
common specification for long-distance carriers in the 1970s and 1980s.
Off-Highway Equipment: Dump trucks, loaders, graders, and other heavy
construction machinery requiring the 8V71T’s compact footprint relative
to power output.
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