Cummins X12 Specifications
| Engine Model: Cummins X12 |
| Engine Type: 4-stroke in-line 6-cylinder turbocharged liquid-cooled diesel |
| Total Displacement: 720 cu.in (11.8 L) |
| Rated Engine Power: 335-513 Hp (250-383 kW) at 2000 rpm |
| Fuel System Type: High Pressure common rail |
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The Cummins X12 is a 11.8-liter, inline
6-cylinder diesel engine engineered as a lightweight, high-power-density
solution for on-highway, vocational, and recreational vehicle
applications. Its design philosophy prioritizes a reduction in overall
package size and mass without compromising structural integrity. This is
achieved through a sculptured cylinder block and the strategic use of
composite materials.
The engine employs the XPI high-pressure common rail fuel system,
enabling precise combustion control that yields a broad, flat torque
curve and high peak power outputs. The X12 is distinguished by its
integrated engine brake, advanced electronic architecture supporting
predictive technologies, and a simplified emissions aftertreatment
system. The engine’s compact dimensions facilitate easier installation
in chassis with spatial constraints, while its power-to-weight ratio
contributes to enhanced payload capacity and vehicle agility.
The engine operates on a 4-stroke diesel cycle with an inline 6-cylinder
configuration. Total displacement is 11.8 Liters (720 cu.in), derived
from a bore of 132 mm (5.2 in) and a stroke of 144 mm (5.67 in). The
aspiration system utilizes turbocharging with a charge air cooler; a
wastegate-equipped turbocharger manages boost pressure across the
operating range. The compression ratio is fixed at 18.3:1.
Power output is application-dependent and varies with model year
calibration. Advertised horsepower spans from 335 HP (250 kW) to 513 HP
(383 kW). For on-highway applications, ratings are typically specified
up to 455 HP or 475 HP. Vocational and recreational vehicle (RV)
calibrations offer higher outputs, reaching 500 HP or 525 HP.
Peak torque output ranges from 1,250 lb-ft (1,695 Nm) to 1,700 lb-ft
(2,305 Nm), with the maximum torque plateau occurring at low engine
speeds between 1,000 RPM and 1,400 RPM. Governed engine speed is set at
2,000 RPM. Clutch engagement torque is specified at 800 lb-ft (1,085
Nm). Dry engine weight is 2,050 lbs (930 kg). The system weight,
inclusive of the engine and the complete aftertreatment system, is 2,241
lbs (1,017 kg).
The cylinder block features a sculptured architecture, a design strategy
that removes non-essential mass from the casting while maintaining high
rigidity in critical load-bearing areas. This configuration reduces the
overall weight of the engine compared to a conventional block of similar
displacement.
The block is constructed from high-strength cast iron. A deep-skirt
design with cross-bolted main bearing caps provides structural support
to the crankshaft and minimizes noise, vibration, and harshness (NVH)
levels.
The cylinder head is a single, cross-flow casting manufactured from gray
iron. It incorporates integrated water jackets for efficient cooling
distribution around the injector sleeves and valve seats. The head is
secured to the block using a multi-layered steel (MLS) head gasket,
which provides a robust seal under high cylinder pressures.
The valve train operates on a 4-valve-per-cylinder configuration, with
two intake and two exhaust valves. The valves are actuated via an
overhead camshaft design, reducing the number of moving parts in the
valvetrain. Valve lash adjustment is achieved using a mechanical,
adjustable rocker arm system.
The valve seat inserts are hardened for durability under the high
thermal and mechanical loads encountered during both power generation
and engine braking operation. An integrated, overhead cam-mounted
compression brake serves as the engine braking system, using the exhaust
valves to convert the engine into a power-absorbing device.
Fuel is delivered via the Cummins XPI (Xtreme Pressure Injection)
high-pressure common rail system. This system decouples pressure
generation from injection timing, allowing for variable injection
pressure independent of engine speed. A high-pressure fuel pump supplies
fuel to a common rail accumulator, which stores fuel at pressures up to
2,000 bar (29,000 psi).
The system supports multiple injection events per combustion cycle,
including pilot, main, and post-injections. Pilot injections reduce
combustion noise, while precise main injection timing optimizes power
and fuel consumption. Post-injections generate thermal energy necessary
for Diesel Particulate Filter (DPF) regeneration.
Electronic control units (ECUs) manage the injector solenoids, which are
capable of delivering highly precise fuel quantities across the entire
speed and load range. This precision ensures consistent combustion
performance at high altitudes and in extreme ambient temperatures. The
fuel system is fully integrated with the engine’s electronic
architecture to enable features such as Adaptive Drive, which adjusts
vehicle performance based on route topography and driving style.
The lubrication system is a forced-feed, full-flow filtration design. A
gear-type oil pump, mounted to the front of the engine, circulates
engine oil to critical components including the crankshaft, connecting
rods, camshaft, and turbocharger bearings. The oil pump capacity is
matched to the engine’s requirements across the operating speed range.
An oil cooler, utilizing engine coolant, maintains oil temperature
within operational limits. The system incorporates a spin-on, full-flow
oil filter with a bypass valve to ensure lubrication continuity in
cold-start conditions or if the filter becomes restricted. The oil pan
is constructed from a high-strength composite material, which
contributes to mass reduction and provides improved acoustic damping
properties compared to a stamped steel pan. The composite material also
offers enhanced resistance to corrosion from road salt and other
environmental contaminants.
The cooling system is a liquid-cooled, pressurized design using a
centrifugal water pump driven by the engine’s front gear train. Coolant
circulation maintains the cylinder block, cylinder head, and charge air
cooler (aftercooler) within defined thermal parameters. A
thermostatically controlled bypass circuit allows for rapid engine
warm-up, reducing cold-start wear and improving combustion efficiency
during initial operation.
The coolant flow path prioritizes the cylinder head to manage thermal
loads in the valve bridge and injector sleeve areas. A separate coolant
loop serves the EGR (Exhaust Gas Recirculation) cooler, reducing the
temperature of recirculated exhaust gas prior to its introduction into
the intake manifold. The system is designed to operate with Extended
Life Coolant (ELC), which provides extended change intervals and
superior cavitation protection for the cylinder liners.
| Intake and Exhaust Systems |
Intake air is drawn through an air cleaner, compressed by the
turbocharger, and then cooled in the charge air cooler before entering
the intake manifold. Exhaust gases are routed through a Diesel Oxidation
Catalyst (DOC), a Diesel Particulate Filter (DPF), and a Selective
Catalytic Reduction (SCR) system to meet emissions regulations. The
engine employs a cooled EGR system to reduce combustion temperatures and
control NOx formation.
Emissions Control: The engine meets EPA 2021/2024 and Euro VI emissions
standards. The aftertreatment system is a compact, integrated design
that combines the DOC, DPF, and SCR in a single assembly. A DEF (Diesel
Exhaust Fluid) dosing system injects fluid upstream of the SCR catalyst
to convert NOx into nitrogen and water vapor.
Engine Braking: An integrated compression brake is housed within the
cylinder head. The system operates by opening the exhaust valves near
the top of the compression stroke, releasing compressed cylinder
pressure to the exhaust manifold. At an engine speed of 2,100 RPM, the
brake delivers up to 390 braking HP, providing substantial retarding
power for grade descent and reducing wear on the foundation brakes.
Electronics and Diagnostics: The engine utilizes a fully electronic
control system with a modular architecture. Features include Cummins
ADEPT (Advanced Dynamic Efficient Powertrain Technology), which uses
route preview to optimize shift schedules and vehicle speed for maximum
fuel efficiency. Connected Diagnostics enables remote monitoring of
engine health, with fault code alerts and proactive service
recommendations delivered via telematics. Predictive Cruise Control uses
GPS data to anticipate terrain changes and adjust vehicle speed to
optimize fuel economy.
0Overall length is 41.5 in (1,054 mm). Width, measured at the widest
point including the exhaust manifold and turbocharger, is 34.0 in (864
mm). Height, measured from the lowest point of the oil pan to the
highest point of the engine, is 39.0 in (991 mm). The dry weight of the
engine is 2,050 lbs (930 kg). The total system weight, which includes
the engine, alternator, starter, and the complete aftertreatment
assembly, is 2,241 lbs (1,017 kg).
Engine oil and filter change intervals are established at 18 months,
1,500 hours, or 40,000 miles (64,000 km), whichever occurs first. The
engine uses a high-performance diesel engine oil meeting Cummins CES
20086 or equivalent specifications. Oil capacity for the system,
including the filter, is 24 quarts (22.7 L).
Fuel filter replacement is required every 12 months, 1,500 hours, or
40,000 miles (64,000 km). The system uses a 10-micron filter element to
protect the high-pressure common rail components from contamination.
Valve lash inspection and adjustment is scheduled for every 6,750 hours
or 300,000 miles (483,000 km). The valve lash clearance for the intake
valves is 0.014 in (0.36 mm) and for the exhaust valves is 0.025 in
(0.64 mm) on a cold engine. The crankcase breather filter is a
maintenance-free component, utilizing a centrifugal separator design
that eliminates the need for periodic replacement.
Coolant replacement interval for Extended Life Coolant (ELC) is 6 years
or 300,000 miles (483,000 km). The total cooling system capacity,
including the engine and radiator, is approximately 31 quarts (29.3 L).
Cylinder head bolts: 150 Nm (111 lb-ft).
Connecting rod cap bolts: 100 Nm (74 lb-ft).
Main bearing cap vertical bolts: 150 Nm (111 lb-ft).
Main bearing cap horizontal cross-bolts: 100 Nm (74 lb-ft).
The flywheel mounting bolts: 180 Nm (133 lb-ft).
Injector hold-down clamp bolts: 22 Nm (16 lb-ft).
Valve rocker arm shaft pedestal bolts: 50 Nm (37 lb-ft).
The Cummins X12 is utilized across a spectrum of heavy-duty vehicle
segments.
On-Highway Trucks: The engine is a popular choice for regional haul and
line-haul applications, particularly in weight-sensitive configurations
such as bulk haulers, tankers, and flatbeds. The low weight and high
torque output enable payload maximization while maintaining competitive
fuel efficiency.
Vocational Trucks: In vocational applications, the engine serves in
concrete mixers, dump trucks, refuse vehicles, and heavy-duty tow
trucks. The engine’s high power-to-weight ratio and integrated engine
brake provide the necessary performance for frequent stop-start cycles
and operation in off-road or urban construction environments.
Recreational Vehicles (RVs): The X12 is a primary powerplant in Class A
diesel motorhomes, including both diesel pusher and front-engine diesel
configurations. The engine is valued for its quiet operation, broad
torque band for hill climbing, and the retarding power of the integrated
brake for descending mountain grades. The compact dimensions facilitate
installation in RV chassis where space is at a premium.
Specialty and Fire Apparatus: The engine is also utilized in severe-duty
applications such as fire trucks and emergency vehicles, where rapid
throttle response, high power density, and reliability are critical
operational requirements.
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