Cummins NTC-400 Specifications
| Engine Model: Cummins NTC-400 |
| Engine Type: 4-stroke in-line 6-cylinder turbocharged liquid-cooled diesel |
| Total Displacement: 855 cu.in (14.0 L) |
| Rated Engine Power: 400 Hp (298 kW) at 2100 rpm |
| Fuel System Type: Pressure-Time fuel system |
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The Cummins NTC-400 represents the pinnacle of
the classic “Big Cam” engine family, a hallmark of heavy-duty diesel
propulsion from the late 1970s through the 1980s. Derived from the
venerable 855 cubic inch (14.0 L) displacement platform, this engine was
the flagship power unit for the most demanding on-highway trucking and
industrial applications of its era.
Its reputation rests on a foundation of extreme durability, mechanical
simplicity, and the revolutionary introduction of the larger 2.5-inch
(63.5 mm) diameter camshaft. This "Big Cam" design allowed for more
aggressive valvetrain profiles, enabling shorter injection durations and
higher fuel injection pressures. The result was a significant leap in
fuel efficiency, transient response, and power output compared to its
predecessors.
The NTC-400 is not merely an engine; it is a benchmark of mechanical
diesel engineering, prized today by collectors and restorers for its
reliability, distinct exhaust note, and the absence of electronic engine
controls. Its architecture, featuring wet cylinder liners and the
Pressure-Time (PT) fuel system, made it a candidate for multiple
in-frame overhauls, granting it a service life that often extended well
beyond a million miles in highway service.
Engine Configuration: Inline 6-cylinder, 4-stroke diesel
Displacement: 14.0 L (855 cu.in)
Bore x Stroke: 140 mm x 152 mm (5.5 in x 6.0 in)
Aspiration: Turbocharged and Aftercooled
Compression Ratio: 14.0:1
Advertised Horsepower: 400 HP (298 kW) @ 2100 RPM
Peak Torque: 1150 lb-ft (1559 Nm) @ 1300-1500 RPM
Governed Speed (No-Load): 2275 RPM (High Idle)
Governed Speed (Rated): 2100 RPM
Clutch Engagement Torque: 650 lb-ft (881 Nm)
Firing Order: 1-5-3-6-2-4
Direction of Rotation: Counter-clockwise (as viewed from the front of
the engine)
The cylinder block is a deep-skirt, cast iron alloy structure designed
for maximum rigidity under high cylinder pressures. The design is
centered on the replaceable wet liner system. The block casting
incorporates water jackets that allow coolant to circulate directly
around the outer circumference of the cylinder liners. This “wet” design
provides superior cooling uniformity, reducing thermal stress and liner
distortion.
The block is cross-bolted in the main bearing area, with four bolts per
bearing cap (two vertical and two angled, or “crossbolts”) to secure the
crankshaft, a feature that reinforces the lower end against the high
torque outputs of the 400 HP rating. The cylinder deck surface is
machined flat to accept the cylinder head, and the block features
integral mounting pads for the fuel pump, water pump, and the large
accessory drive case. The serial number and engine model designation are
stamped on a machined pad located on the right side of the block, just
above the fuel pump mounting.
The cylinder head is a single, high-strength cast iron unit spanning all
six cylinders. It is secured to the block by 26 head bolts arranged in a
specific pattern to ensure uniform clamping force across the fire deck.
The head features a cross-flow design, with intake ports on the right
side and exhaust ports on the left, optimizing airflow efficiency.
The valve train is actuated by the large-diameter Big Cam, which drives
pushrods that operate the rocker levers. The valve arrangement is
inline, with two valves per cylinder (one intake, one exhaust). Valve
lash adjustments are critical for performance and durability.
Intake Valve Diameter: 2.375 in (60.3 mm)
Exhaust Valve Diameter: 2.000 in (50.8 mm)
Valve Lash (Intake): 0.010 in (0.25 mm) (cold)
Valve Lash (Exhaust): 0.020 in (0.51 mm) (cold)
Valve Seat Angle: 45 degrees
The NTC-400 utilizes the Cummins PT (Pressure-Time) fuel system, a
purely mechanical, low-pressure design that distinguishes it from unit
injector or common rail systems. The system operates on the principle
that the volume of fuel injected into a cylinder is a function of fuel
pressure and the time the injector is open. Fuel is drawn from the tank
by a gear-type fuel pump, which supplies fuel at a regulated pressure
(ranging from 60 to 180 psi depending on engine speed and load) to the
cylinder head.
The cylinder head itself acts as a fuel gallery. Camshaft-actuated,
single-orifice injectors, one per cylinder, are mounted directly in the
cylinder head. The camshaft lobe strikes the injector rocker lever,
which presses down on the injector plunger to open the metering orifice.
The duration of this opening is fixed by the cam profile, while the fuel
pressure determines the volume injected.
This system is noted for its simplicity, high reliability, and ease of
tuning through the adjustment of the fuel pump and injector timing. A
manual fuel shut-off lever is located on the fuel pump for emergency
shutdown. Injector timing, often referred to as “plunger travel,” is a
critical manual adjustment performed during an overhead set.
The lubrication system is a full-pressure, full-flow design utilizing a
gear-type oil pump mounted internally to the front gear train. The pump
draws oil from a large-capacity sump through a strainer and forces it
through a spin-on, full-flow lube oil filter. A bypass valve ensures oil
flow to the engine even if the filter becomes restricted.
The system also incorporates a piston cooling system, which uses oil
jets - or “piston cooling nozzles” - aimed at the underside of each
piston crown to dissipate the intense heat generated at 400 HP. These
nozzles are crucial for piston ring and skirt longevity. Oil Pan
Options: Available in front-sump, rear-sump, and center-sump
configurations to accommodate various vehicle chassis rail heights and
suspension systems.
Oil System Capacity (including filters): 11.5 U.S. gal (43.5 L)
Oil Pressure (Operating, @ 2100 RPM): 50-70 psi (345-483 kPa)
Oil Pressure (Low Idle, @ 600 RPM): 15-30 psi (103-207 kPa)
The cooling system is designed to manage the substantial thermal load
generated by the turbocharged and aftercooled configuration. It utilizes
a centrifugal-type water pump driven by the accessory drive belt system.
Coolant flow is directed through the block to the cylinder liners and
then upward into the cylinder head. A critical component of the cooling
system is the aftercooler, which reduces the temperature of the
compressed intake air before it enters the cylinder.
Two primary configurations exist:
Jacket-Water Aftercooler (JWAC): Utilizes the engine’s own coolant to
cool the intake air. This system is simpler but limits the degree of
charge air cooling.
Air-to-Air Aftercooler (ATAAC): This chassis-mounted system uses the
vehicle’s forward motion and a separate radiator to cool the intake air
to temperatures lower than the engine coolant. ATAAC provides denser
intake air, resulting in higher efficiency and lower combustion
temperatures, which was the preferred configuration for maximizing power
and durability in the NTC-400.
Coolant Capacity (Engine only): 10.0 U.S. gal (37.9 L).
Thermostat Opening Temperature: 180°F (82°C)
Water Pump Type: Centrifugal, with seal and bearing assembly designed
for high belt loads.
Air Intake System: The engine is equipped with a Holset turbocharger, a
model HX-80 or similar, sized for the 400 HP rating. The turbocharger
features a wastegate to control boost pressure and prevent over-speeding
at high altitudes. The intake manifold is integrated into the cylinder
head casting.
Electrical System: The engine is equipped with a 12-volt or 24-volt
starting system, featuring a gear-reduction starter motor for high
cranking torque. The alternator is belt-driven and typically ranges from
65 to 130 amperes depending on the vehicle specification.
Governor: The system employs a mechanical, all-speed governor integrated
into the PT fuel pump. It controls engine speed from idle to the
governed maximum, maintaining the set RPM regardless of load within the
engine’s torque capability.
Dry Weight: 2600 lb (1179 kg)
Length (from fan to flywheel housing): 52.3 in (1328 mm)
Width (overall, at rocker covers): 34.0 in (864 mm)
Height (overall, from oil pan rail to rocker cover): 41.5 in (1054 mm)
Oil and Filter Change Interval: Recommended at 10,000-15,000 miles
(16,000-24,000 km) for highway use, using API CD or CE classification
oil. Capacity includes both the engine sump and the full-flow filter.
Valve and Injector Adjustment (Overhead Set): A critical maintenance
procedure performed every 50,000-100,000 miles (80,000-160,000 km). This
process, known as a “major overhead,” requires the manual adjustment of
intake and exhaust valve lash and the injector plunger travel. The
injector timing is set by measuring the travel of the injector plunger
with a dial indicator while adjusting the rocker lever.
Coolant Maintenance: The engine requires strict adherence to
Supplemental Coolant Additive (SCA) levels. The wet cylinder liners are
subject to pitting and cavitation erosion if the SCA concentration is
not maintained between 1.5 and 3.0 units per gallon. Coolant should be
tested regularly and changed at intervals specified by the coolant
manufacturer.
Fuel Filter Replacement: Primary and secondary spin-on fuel filters are
replaced at alternating intervals, generally every 10,000-15,000 miles
(16,000-24,000 km), to ensure the integrity of the PT fuel system.
Air Filter Maintenance: The dry-type air filter elements must be
serviced based on restriction gauge readings. Restricted air intake
leads to high exhaust temperatures and reduced turbocharger life.
Cylinder Head Bolts: 225 lb-ft (305 Nm) + 90-deg turn.
Connecting Rod Bolts: 75 lb-ft (102 Nm) + 60-deg turn.
Main Bearing Cap Bolts (Vertical): 180 lb-ft (244 Nm)
Main Bearing Cap Bolts (Crossbolts): 95 lb-ft (129 Nm)
Rocker Lever Hold-Down Bolts: 100 lb-ft (136 Nm)
Fuel Pump Mounting Nuts: 30 lb-ft (41 Nm)
Injector Hold-Down Clamp: 30 lb-ft (41 Nm)
Flywheel Housing to Block: 50 lb-ft (68 Nm)
Vibration Damper (Crankshaft Pulley): 450 lb-ft (610 Nm)
The NTC-400 was specified for the most severe heavy-duty applications
where maximum power and reliability were required.
Heavy Duty Trucking: The engine was a dominant force in the North
American Class 8 market, powering iconic long-haul and heavy-haul
tractors. It was a preferred engine in Kenworth W900, Peterbilt 359 and
379, Freightliner FLC and FLD, International 9300 and 9700, and Mack
Ultra-Liner chassis. It was the engine of choice for logging, heavy
equipment transport (lowboy), and livestock hauling due to its high
torque rise and engine braking capability.
Construction and Mining: The engine’s robust construction made it
suitable for off-highway equipment. It was utilized in Caterpillar,
Komatsu, and Terex haul trucks (such as the 33-series), large
rubber-tired loaders, Euclid scrapers, and various models of mobile
cranes and draglines where a high-power, mechanically governed diesel
was essential for consistent operation in dusty and remote environments.
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