Cummins ISX12N Specifications
| Engine Model: Cummins ISX12N |
| Engine Type: 4-stroke in-line 6-cylinder turbocharged liquid-cooled natural gas |
| Total Displacement: 726 cu.in (11.9 L) |
| Rated Engine Power: 330-400 Hp (246-298 kW) at 2100 rpm |
| Fuel System Type: Natural gas injector |
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The Cummins ISX12N is an advanced heavy-duty
natural gas engine designed for Class 8 trucks, vocational equipment,
transit buses, and specialized industrial platforms requiring ultra-low
emissions, reduced operating cost, and reliable performance. As the
successor to earlier engines such as the ISL G and ISX12 G, the ISX12N
incorporates next-generation combustion control, optimized spark
ignition, cooled EGR (depending on configuration), and a robust
three-way catalyst (TWC) aftertreatment system.
Certified to near-zero NOx levels-including CARB Optional Low NOx-the
ISX12N is engineered for fleets adopting alternative fuels including
CNG, LNG, and RNG. Its design emphasizes fuel efficiency, simpler
aftertreatment (no DPF or SCR), improved transient response, and reduced
maintenance needs compared to diesel counterparts.
The ISX12N is a four-stroke, inline six-cylinder natural gas engine with
a displacement of 11.9 liters (726 cubic inches). Bore measures 130 mm
(5.12 inches), stroke measures 150 mm (5.91 inches). Compression ratio
generally ranges from 11.5:1 to 12.0:1. Rated power output ranges
between 330 and 400 horsepower (246-298 kW) at 1800-2100 rpm.
Peak torque typically ranges from 1350 to 1800 Nm (996-1328 lb-ft),
available at 1200-1400 rpm. Idle speed is generally 600-650 rpm. Firing
order is 1-5-3-6-2-4. Spark ignition replaces diesel compression
ignition, using high-energy coil-on-plug ignition modules. Turbocharging
optimizes boost for stoichiometric combustion. The ECM governs spark
timing, fuel metering, knock response, and protection strategies.
The cylinder block is cast from high-strength iron designed to withstand
the thermal and mechanical loads of spark-ignited natural gas
combustion. Reinforced ribs increase strength and minimize vibration.
The forged-steel crankshaft is carried by seven main bearings engineered
for longevity in high-duty cycles. Wet replaceable liners offer superior
cooling and simplify overhaul.
Machined oil galleries provide lubrication to main bearings, connecting
rods, camshaft journals, and piston cooling jets. Integrated coolant
jackets distribute heat evenly throughout the block. Accessory mounting
provisions support alternators, air compressors, PTO drives, HVAC
compressors, and hydraulic pumps.
The cast-iron cylinder head features optimized natural gas combustion
chambers. Each cylinder uses four valves-two intake and two exhaust-for
strong airflow and efficient burn. Valvetrain actuation uses rocker arms
and pushrods driven by a block-mounted camshaft. Exhaust valves are
constructed from heat-resistant alloys due to elevated natural gas
combustion temperatures.
Hardened seats maintain sealing integrity under continuous load.
Integrated coolant passages improve thermal stability and reduce gasket
stress. Multi-layer steel head gaskets are used for durability under
high firing pressures.
The ISX12N operates on spark-ignited stoichiometric combustion using
natural gas injectors, regulators, and electronically modulated fuel
control valves. CNG, LNG, or RNG can be used. Fuel pressure ranges
between 7 and 10 bar (102-145 psi).
The ECM adjusts injection timing, spark advance, and air-fuel ratios
based on knock detection, cylinder pressure, oxygen sensor feedback,
intake temperature, coolant temperature, and fuel quality. Coil-on-plug
ignition ensures high-energy spark delivery. Stoichiometric operation
allows the use of simple TWC aftertreatment instead of diesel DPF/SCR
equipment.
The lubrication system is a full-pressure wet-sump configuration using a
gear-driven oil pump. Oil passes through a strainer and full-flow filter
before entering the main gallery. Pressurized oil reaches crankshaft
bearings, connecting rods, camshaft bearings, rocker assemblies, and
turbocharger bearings.
Piston cooling jets maintain stable crown temperatures. Standard
operating oil pressure is 300-500 kPa (44-72 psi), with idle pressure
between 100-150 kPa (15-22 psi). Oil capacity ranges from 28 to 38
liters (29.6-40.1 US quarts). Specialized low-ash natural-gas engine oil
is required to protect catalyst systems.
A liquid-cooling system maintains thermal stability. A belt-driven
centrifugal water pump circulates coolant through block and head
passages. The thermostat begins opening at 82°C (180°F) and is fully
open near 95°C (203°F). Cooling system pressure ranges from 90-110 kPa
(13-16 psi).
Coolant capacity ranges from 40 to 55 liters (42.2-58.1 US quarts).
Charge-air cooling lowers intake temperature, stabilizing combustion and
reducing NOx formation. Proper coolant chemistry prevents corrosion,
scaling, and cavitation. ECM controls derate logic to prevent
overheating.
Turbocharging uses wastegated or variable-geometry turbochargers. The
exhaust system uses a three-way catalyst sized for heavy-duty natural
gas combustion. Electrical systems operate on 12- or 24-volt
configurations with alternators rated at 100-150 amperes. Sensors feed
ECM logic for spark control, knock detection, fuel delivery, and
emissions compliance. Crankcase ventilation systems include
high-efficiency separators to reduce oil carryover. No diesel
aftertreatment (DPF or SCR) is required.
Length: 1350-1550 mm (53.1-61.0 in)
Width: 800-950 mm (31.5-37.4 in)
Height: 1150-1450 mm (45.3-57.1 in)
Dry weight: 900-1150 kg (1984-2535 lb), depending on turbocharger type,
aftertreatment, and accessories.
Oil and filter changes: every 500 hours or specified mileage.
Fuel filters/regulators: inspect and service every 500-1000 hours.
Air filter: replace every 200-400 hours depending on dust exposure.
Coolant: replace every two years.
Ignition system: spark plugs, coil, and leads require regular inspection
and replacement.
TWC aftertreatment: periodic inspection for backpressure or
contamination.
ECM diagnostics: use logs for predictive maintenance and emissions
verification.
Cylinder head bolts: 220-260 Nm (162-192 lb-ft)
Main bearing caps: 180-220 Nm (133-162 lb-ft)
Connecting rod bolts: 90-120 Nm (66-89 lb-ft)
Flywheel bolts: 300-350 Nm (221-258 lb-ft)
Crankshaft pulley bolt: 280-320 Nm (207-236 lb-ft)
Ignition coil bolts: 10-15 Nm (7-11 lb-ft)
Spark plugs: 25-30 Nm (18-22 lb-ft)
Oil drain plug: 40-50 Nm (30-37 lb-ft)
The ISX12N powers refuse trucks, regional-haul tractors, municipal
fleets, transit buses, school buses, airport service vehicles, utility
trucks, industrial power units, and renewable natural gas fleets. Its
extremely low emissions profile, reduced operating cost, and
compatibility with clean-fuel initiatives make it popular for
environmentally regulated markets.
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