Cummins ISX-400ST Specifications
| Engine Model: Cummins ISX-400ST |
| Engine Type: 4-stroke in-line 6-cylinder turbocharged liquid-cooled diesel |
| Total Displacement: 912 cu.in (15 L) |
| Rated Engine Power: 400 Hp (298 kW) at 2000 rpm |
| Fuel System Type: High-Pressure Injection |
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The Cummins ISX-400ST represents a specific
power rating within the renowned ISX series, a heavy-duty diesel engine
platform that set industry standards for durability, performance, and
electronic integration. Designed primarily for line-haul and regional
trucking applications, the 400ST variant was engineered to balance
robust power delivery with exceptional fuel efficiency.
The “ST” designation signifies a “Smart Torque” calibration, a feature
that allowed the engine to automatically adjust its torque output based
on the selected gear. This provided the operator with lower torque in
the lower gears for improved traction and drivability in starting
conditions, seamlessly increasing to a higher torque peak in the top two
gears for superior highway performance and reduced shifting.
The ISX platform is characterized by its advanced dual overhead camshaft
(DOHC) architecture, a deep-skirted cylinder block for structural
rigidity, and the use of a variable geometry turbocharger (VGT) for
responsive boost across the operating range. Over its production
lifecycle, the engine saw significant evolution in its fuel systems,
transitioning from the High Pressure Injection (HPI) system to the more
advanced XPI common-rail system, further refining combustion efficiency
and emissions control.
Engine Type: 6-Cylinder in-line, 4-Stroke Diesel
Displacement: 15.0 L (912 cu.in)
Advertised Power: 400 hp (298 kW) at 1800-2000 RPM
Governed Speed: 2000-2100 RPM (high idle); 800-900 RPM (low idle)
Clutch Engagement Torque: 1000 lb-ft (1356 Nm) at 800 RPM
Bore x Stroke: 5.39 in x 6.65 in (137 mm x 169 mm)
Compression Ratio: 19.0:1
Peak Torque Speed: 1200 RPM
Oil System Capacity (including filters): 14 U.S. gal (52.9 L)
Engine Brake: Integrated system rated at up to 600 hp (447 kW) of
braking power.
Torque Calibrations: The ISX-400ST features two primary smart torque
calibrations that provide variable output based on gear selection to
optimize drivability and fuel economy: 1450/1650 lb-ft: Delivers 1450
lb-ft (1966 Nm) in lower gears, increasing to 1650 lb-ft (2237 Nm) in
the top two gears. 1550/1750 lb-ft: Delivers 1550 lb-ft (2102 Nm) in
lower gears, increasing to 1750 lb-ft (2373 Nm) in the top two gears.
The cylinder block is a deep-skirt, high-strength cast iron design. This
architecture extends the block skirts below the crankshaft centerline,
providing exceptional rigidity and reducing noise, vibration, and
harshness. The deep-skirt design also allows for the use of cross-bolted
main bearing caps, which are secured with both vertical and horizontal
fasteners.
This configuration significantly enhances the block’s ability to
withstand high cylinder pressures generated by the advanced fuel systems
and turbocharging, ensuring long-term durability in heavy-duty
applications. The block incorporates replaceable wet-type cylinder
liners.
The engine utilizes a crossflow cylinder head manufactured from
high-strength cast iron. It features a dual overhead camshaft (DOHC)
arrangement prevalent on ISX models from 1999 through 2009. In this
configuration, one camshaft is dedicated to operating the fuel injectors
(in HPI models) while the second camshaft operates the intake and
exhaust valves as well as the engine brake mechanism.
This separation of functions allowed for optimized cam profiles for both
power generation and auxiliary braking. The valvetrain employs four
valves per cylinder - two intake and two exhaust - arranged to center
the fuel injector within the combustion chamber. This promotes superior
air-fuel mixing and combustion efficiency. Valve bridges are used to
actuate the two valves from a single cam lobe. The overhead cam design
eliminates the need for pushrods, reducing reciprocating mass and
contributing to the engine’s high RPM operational capability and
structural integrity.
The fuel system for the ISX-400ST varies by model year. Early versions
are equipped with the High Pressure Injection (HPI) system. This system
uses a single, high-pressure, engine-driven fuel pump to supply fuel to
individual electronic unit injectors (EUI). The injectors are actuated
mechanically by the dedicated camshaft, allowing injection pressures of
up to 23,000 psi (1585 bar). This system provides precise electronic
control over injection timing and duration.
Later model versions of the ISX-400ST transitioned to the XPI (Xtreme
Pressure Injection) common-rail fuel system. This advanced system
utilizes a high-pressure supply pump to deliver fuel to a common rail
which acts as an accumulator. The rail maintains a constant, high
pressure, feeding electronically controlled fuel injectors.
The XPI system operates at injection pressures up to 35,000 psi (2413
bar), enabling finer atomization of fuel for improved combustion
efficiency, reduced emissions, and lower noise. The transition to XPI
also allowed for multiple injection events per combustion cycle, such as
pilot, main, and post injections, further refining performance and
enabling advanced aftertreatment management.
The lubrication system is a full-flow, forced-feed system with a
high-capacity gear-type pump mounted on the front of the engine. It
draws oil from a sump, which can be either a front or center
configuration depending on the chassis application. The system is
designed to maintain consistent oil pressure across all operating
conditions. Filtration is achieved through a full-flow spin-on filter,
with an optional bypass filter available for enhanced oil cleanliness in
extended service intervals.
The deep-skirt block and cross-bolted main bearing design necessitate a
robust lubrication circuit to ensure all critical bearing surfaces,
camshafts, and the turbocharger receive adequate oil flow, particularly
under high-load and low-speed conditions where peak torque is generated.
The cooling system employs a centrifugal water pump driven by the front
gear train. Coolant flow is directed through the cylinder block and into
the cylinder head using a rear-entry, front-exit cooling strategy. This
ensures even thermal distribution across all six cylinders, mitigating
the risk of localized hot spots and managing thermal expansion
uniformly.
A coolant conditioner system is integrated to prevent corrosion and
cavitation erosion of the wet cylinder liners. The system is designed to
interface with a chassis-mounted radiator, charge-air cooler, and a
coolant filter that also introduces supplemental coolant additives
(SCAs) into the coolant stream.
Air Intake and Turbocharging: The engine is equipped with a Variable
Geometry Turbocharger (VGT) with electric actuation. The VGT alters the
angle of the turbine vanes to optimize airflow across the engine speed
range. At low RPM, the vanes close to increase exhaust velocity and
spool the turbocharger quickly, reducing lag. At higher RPM, the vanes
open to reduce backpressure and improve fuel efficiency. This system is
paired with a dual-element air cleaner and a chassis-mounted charge-air
cooler to reduce intake air temperature before it enters the cylinder
head.
Engine Braking: The Intebrake is an integrated compression-release
engine brake that utilizes the dedicated camshaft and hydraulic lash
adjusters to open the exhaust valves near the top of the compression
stroke. By releasing the compressed air, the system dissipates energy
and provides substantial retarding power. The system offers multiple
stages of braking power, allowing the driver to match retarding force to
road conditions and load.
Emissions Control: To meet EPA emissions standards, the ISX-400ST
utilizes Cooled Exhaust Gas Recirculation (EGR). A portion of the
exhaust gas is cooled and rerouted back into the intake air stream to
lower combustion temperatures, reducing the formation of nitrogen oxides
(NOx). Later models equipped with the XPI fuel system also incorporate a
Cummins Particulate Filter (DPF) in the aftertreatment system to trap
and oxidize soot and ash from the exhaust stream, requiring periodic
regeneration cycles to burn off accumulated particulate matter.
Dry Engine Weight: 3021 lb (1370 kg).
Total System Weight: 3093 lb (1403 kg).
Length: 54 in (1372 mm) from the fan hub to the flywheel housing.
Width: 40 in (1016 mm) at the widest point, typically the exhaust
manifold or turbocharger.
Height: 52 in (1321 mm) from the bottom of the oil pan to the top of the
rocker cover.
Oil Change Interval: Up to 25,000 miles (40,000 km) or 500 hours under
normal highway duty, subject to oil analysis. Severe service intervals
are reduced. Fuel Filter Change: Replacement of the primary (pre-filter)
and secondary (spin-on) filters at every oil change interval.
Valve Lash (Intake and Exhaust): 0.015 in (0.38 mm) for both intake and
exhaust valves, measured with the engine cold. The dual overhead cam
design simplifies adjustment through the use of adjustable crossheads or
shim-style adjustment.
Coolant Change Interval: Extended life coolant (ELC) change interval is
300,000 miles (480,000 km) or 6 years, with supplemental coolant
additive (SCA) levels checked and maintained at each oil change. Air
Filter Service: Inspect at each oil change; replace based on restriction
gauge reading, not on a timed interval.
Cylinder Head Bolts (M20): 200 lb-ft (271 Nm)
Main Bearing Cap Bolts (Vertical): 100 lb-ft (136 Nm).
Main Bearing Cap Bolts (Cross-bolts): 80 lb-ft (108 Nm).
Connecting Rod Bolts: 110 lb-ft (149 Nm).
Flywheel to Crankshaft: 180 lb-ft (244 Nm).
Vibrations Damper to Crankshaft: 350 lb-ft (475 Nm).
Fuel Injector Clamp (HPI System): 44 lb-ft (60 Nm).
Valve Cover: 10 lb-ft (14 Nm).
The Cummins ISX-400ST was predominantly utilized in heavy-duty
on-highway commercial vehicles. Its smart torque calibration made it
particularly suited for applications requiring a balance of starting
traction and highway fuel economy.
Line-haul and Regional Tractor-Trailers: The 400ST rating was a popular
choice for fleets operating in variable terrain where the combination of
lower starting torque and increased top-gear torque offered a
competitive advantage in fuel efficiency without sacrificing
grade-climbing capability.
Heavy-Duty Dump Trucks and Mixers: Select vocational applications
utilized this rating where a predictable power band and robust engine
braking were essential for operation in construction environments.
Motorcoaches and Buses: The smooth power delivery and integrated engine
brake made the ISX-400ST a viable option for high-end motorcoach
applications demanding reliability and passenger comfort over long
distances.
Refuse Haulers: In some applications, the durability of the platform and
the engine brake’s contribution to reducing service brake wear led to
its use in refuse collection vehicles, though vocational-specific
ratings were more common.
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