Mitsubishi G54B Specifications
| Engine Model: Mitsubishi G54B |
| Engine Type: 4-cycle inline 4-cylinder SOHC 8-valve liquid-cooled gasoline |
| Total Displacement: 155.9 cu.in (2.55 L) |
| Rated Engine Power: 103-175 Hp (77-130 kW) at 5500 rpm |
| Fuel System Type: Carburetor or multi-point fuel injection |
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The Mitsubishi G54B, designated within the Astron
engine family and also known as the 4G54, is a 2.6-liter inline-four powerplant
that became a cornerstone of Mitsubishi’s engine lineup throughout the 1980s.
Its most distinctive feature is the "Silent Shaft" technology - a dual balancing
shaft system that significantly reduced the secondary vibration inherent to
large-displacement inline-four engines, delivering a level of smoothness
uncommon in its class.
The engine gained widespread recognition for powering the Mitsubishi Starion
Turbo, the Mighty Max pickup, and numerous Chrysler-branded vehicles including
the Dodge D-50 and Plymouth Sapporo. The G54B was offered in both naturally
aspirated carbureted configurations and turbocharged fuel-injected variants
(ECI-Turbo), with the latter establishing a strong aftermarket following due to
its robust bottom end and tuning potential.
A defining characteristic of the cylinder head is the MCA-Jet (Mitsubishi Clean
Air) system, which introduced a small auxiliary valve in each cylinder to
generate swirl for improved emissions control. Despite its durability, the
engine is sensitive to cooling system maintenance, as overheating can induce
cracking in the cylinder head around the jet valve areas.
The G54B is a 4-stroke, inline 4-cylinder, water-cooled gasoline engine
utilizing a single overhead camshaft (SOHC) valvetrain with two valves per
cylinder, supplemented by the MCA-Jet system. Total displacement is 2.555 Liters
(2,555 cc / 155.9 cu.in), derived from a bore of 91.1 mm (3.587 in) and a long
stroke of 98.0 mm (3.858 in). The long-stroke configuration contributes to the
engine’s high torque output at low engine speeds.
The compression ratio varies significantly based on induction method and market
requirements: naturally aspirated versions employ ratios between 8.2:1 and
8.7:1, while turbocharged variants utilize lower ratios ranging from 7.0:1 to
8.0:1 to accommodate forced induction pressures. The firing order follows
1-3-4-2. Power and torque outputs vary widely: naturally aspirated carbureted
versions produce 103-114 HP (77-85 kW) with torque ranging from 188-198 Nm
(139-146 lb-ft). Turbocharged ECI-Turbo variants deliver 145-175 HP (108-130 kW)
and torque outputs between 250-310 Nm (184-229 lb-ft), depending on boost
pressure and engine management calibration.
The cylinder block is constructed from cast iron using
a deep-skirt design that extends below the crankshaft centerline, providing
exceptional rigidity for the rotating assembly. The bore diameter is finished to
91.1 mm (3.587 in). The defining feature of the G54B block is the integration of
the Silent Shaft system - a pair of counter-rotating balance shafts located
within the crankcase, driven by a dedicated chain from the crankshaft.
These shafts rotate at twice engine speed to cancel the secondary vibration
forces inherent to inline-four engines, resulting in operational smoothness
comparable to a V6. The crankshaft is forged steel with induction-hardened
journals and is supported by five main bearings. Connecting rods are forged
steel with a full-floating wrist pin design. Pistons are cast aluminum with a
slipper-skirt design; turbocharged variants utilize thicker crowns and lower
compression height to accommodate the reduced compression ratio and higher
thermal loads.
The cylinder head is manufactured from aluminum alloy,
a material selection that reduces overall engine weight and improves heat
dissipation. The SOHC valvetrain operates eight primary valves - two per
cylinder - with the intake and exhaust valves arranged in a cross-flow pattern.
Valve diameters measure 44.0 mm (1.732 in) for intake and 38.0 mm (1.496 in) for
exhaust.
The MCA-Jet system adds a third auxiliary valve per cylinder, known as the jet
valve, positioned adjacent to the primary intake valve. This small valve opens
under light-load conditions to generate a high-velocity swirling motion within
the combustion chamber, improving air-fuel mixing and reducing hydrocarbon
emissions. The jet valves are spring-loaded and actuated by a dedicated rocker
arm.
Valve clearance adjustments are performed with the engine at operating
temperature. Intake valve clearance is set to 0.15 mm (0.006 in), exhaust valve
clearance to 0.25 mm (0.010 in), and jet valve clearance to 0.25 mm (0.010 in).
The jet valve clearance is critical for idle stability and emissions
performance. The camshaft is driven by a dual-chain system - a primary chain
from the crankshaft drives the camshaft sprocket, while a secondary chain drives
the balance shaft assembly.
The fuel system configuration depends on the induction
variant. Naturally aspirated engines are equipped with a downdraft or sidedraft
carburetor, either a Mikuni or a Mitsubishi-built unit, incorporating an
automatic choke and a variety of emission control devices. Turbocharged variants
utilize the ECI-Turbo (Electronic Controlled Injection) system, a multi-point
fuel injection system with injectors mounted in the intake manifold runners.
The ECI system is managed by an engine control unit that receives inputs from
airflow, coolant temperature, throttle position, and knock sensors. Fuel
pressure is regulated at 2.5-3.0 bar (36-44 psi) for turbo applications. The
intake manifold is cast aluminum, with turbocharged versions incorporating a
larger plenum and reinforced mounting flanges for the throttle body. The fuel
system on both variants includes a fuel return line to prevent vapor lock and
maintain consistent fuel temperature.
The lubrication system is a full-flow, pressurized
design utilizing a gear-type oil pump driven directly by the crankshaft. The oil
pump is mounted within the front cover and supplies oil to a full-flow spin-on
oil filter. Total oil capacity ranges from 4.0 to 4.5 Liters (4.2-4.8 qt)
depending on the filter size and the presence of an oil cooler on turbocharged
models.
The Silent Shaft system relies on pressurized oil delivered through dedicated
passages in the cylinder block to the balance shaft bearings; oil pressure must
be maintained within specification to prevent bearing noise and premature shaft
wear. Turbocharged variants incorporate a water-cooled oil cooler mounted
between the oil filter and the engine block, which stabilizes oil temperature
during sustained high-load operation.
Oil pressure at operating temperature ranges from 2.0-4.0 bar (29-58 psi) across
the normal speed range. The recommended oil viscosity is 10W-40 or 15W-40 for
older engine blocks, with a preference for formulations containing adequate
zinc-based anti-wear additives to protect the flat-tappet valvetrain.
The cooling system is a water-cooled, pressurized
design utilizing a belt-driven centrifugal water pump mounted to the front of
the cylinder block. Coolant circulates through the cast-iron block and aluminum
cylinder head, with a cross-flow radiator configuration employed in most vehicle
applications. The thermostat is a wax-pellet unit with an opening temperature of
82°C (180°F) for standard applications, achieving full open at 95°C (203°F).
Turbocharged variants utilize a larger-capacity radiator and, in some markets,
an auxiliary electric cooling fan to manage the additional thermal load
generated under boost. Total coolant capacity ranges from 7.0-8.5 Liters
(7.4-9.0 qt) depending on vehicle platform and heater core configuration. The
cooling system is critical to engine longevity, as the aluminum cylinder head is
susceptible to cracking when subjected to overheating events, particularly in
the area surrounding the jet valve seats.
Silent Shaft System: The twin balance shafts are housed
within the cylinder block, positioned on either side of the crankshaft. The
shafts are driven by a dedicated chain from the crankshaft, with the chain
tension maintained by a hydraulic tensioner supplied by the engine lubrication
system. The shafts rotate in opposite directions at twice crankshaft speed,
generating a counter-vibration that cancels the secondary inertial forces of the
piston and connecting rod assembly. The chain guides are constructed from
polymer materials and are subject to wear over extended service intervals; worn
guides produce a distinctive "chainsaw" noise from the front of the engine and
can lead to chain failure if not addressed.
MCA-Jet System: The jet valve assembly consists of a small poppet valve, a
spring, and a rocker arm integrated into the cylinder head. The system is
calibrated to open under intake vacuum conditions, drawing a small volume of air
through a calibrated orifice. This high-velocity airstream creates a swirling
motion within the combustion chamber that promotes more complete combustion,
enabling leaner air-fuel ratios without misfire. The jet valves require periodic
clearance adjustment and are sensitive to carbon accumulation, which can cause
sticking and lead to rough idle or increased emissions.
Ignition System: Distributor-type ignition is employed across all variants. The
distributor is driven by the camshaft and incorporates mechanical and vacuum
advance mechanisms. Naturally aspirated engines utilize a conventional ignition
coil and spark plug gap of 1.0-1.1 mm (0.039-0.043 in). Turbocharged variants
employ a gap of 0.7-0.8 mm (0.028-0.031 in) to ensure reliable ignition under
elevated cylinder pressures. The distributor on ECI-Turbo models includes a
crank angle sensor that provides engine position data to the electronic control
unit.
Turbocharger System (ECI-Turbo variants): The turbocharger is a single unit
mounted to a cast-iron exhaust manifold. Boost pressure is regulated by an
internal wastegate actuator calibrated to between 0.35-0.60 bar (5-9 psi)
depending on market and model year. The turbocharger features an oil-fed bearing
housing with water cooling in later production variants to prevent oil coking
after shutdown. An air-to-air intercooler is incorporated in higher-output
versions to reduce charge air temperatures.
Length measured from the front accessory drive face to
the transmission mounting flange is 620 mm (24.4 in). Width across the cylinder
head, intake manifold, and exhaust manifold measures 540 mm (21.3 in). Height
from the oil pan bottom surface to the top of the valve cover is 690 mm (27.2
in). The dry weight of the naturally aspirated engine is 160 kg (353 lbs);
turbocharged variants with the ECI system and intercooler piping add an
additional 15-20 kg (33-44 lbs).
The timing chain system does not have a mandatory
replacement interval but should be inspected for elongation, guide wear, and
tensioner function at 100,000 km (60,000 mile) intervals. The Silent Shaft chain
guides are subject to wear and may require replacement at similar intervals.
Engine oil and filter changes are recommended at 5,000 km (3,000 miles) or six
months under normal driving conditions, with shorter intervals for turbocharged
variants.
Valve clearance adjustments, including the jet valves, are specified every
30,000 km (18,000 miles) with the engine at operating temperature. The jet valve
clearance is critical; incorrect adjustment leads to rough idle and elevated
hydrocarbon emissions. Spark plug replacement is recommended at 20,000 km
(12,000 miles) for standard plugs and 40,000 km (25,000 miles) for
platinum-tipped variants. The distributor cap, rotor, and ignition wires should
be inspected annually.
Coolant replacement is recommended every 24 months or 40,000 km (25,000 miles).
Compression pressure for naturally aspirated engines should measure 1.2-1.4 MPa
(174-203 psi) with minimum service limit of 1.0 MPa (145 psi); turbocharged
variants operate at slightly lower compression due to the reduced ratio. The
ECI-Turbo fuel filter should be replaced at 30,000 km (18,000 mile) intervals to
protect the fuel injectors from contamination.
Cylinder Head Bolts (Cold), Step 1: 50 Nm (37 lb-ft).
Cylinder Head Bolts (Cold), Step 2: 90 Nm (66 lb-ft).
Main Bearing Cap Bolts: 80-90 Nm (59-66 lb-ft).
Connecting Rod Cap Bolts: 50-55 Nm (37-41 lb-ft).
Crankshaft Damper Pulley Bolt: 180-200 Nm (133-148 lb-ft).
Camshaft Sprocket Bolt: 60-70 Nm (44-52 lb-ft).
Rocker Arm Shaft Bolts: 25-30 Nm (18-22 lb-ft).
Jet Valve Rocker Arm Shaft Bolts: 12-15 Nm (9-11 lb-ft).
Valve Cover Bolts: 5-7 Nm (44-62 lb-in).
Intake Manifold Bolts: 20-25 Nm (15-18 lb-ft).
Exhaust Manifold Nuts: 20-25 Nm (15-18 lb-ft).
Oil Pan Bolts: 10-12 Nm (7-9 lb-ft).
Water Pump Bolts: 20-25 Nm (15-18 lb-ft).
Flywheel / Drive Plate Bolts: 100-110 Nm (74-81 lb-ft).
Balance Shaft Chain Tensioner Bolts: 10-12 Nm (7-9 lb-ft).
Balance Shaft Bearing Cap Bolts: 20-25 Nm (15-18 lb-ft).
Engine Mount Bracket Bolts: 55-65 Nm (41-48 lb-ft).
The Mitsubishi G54B engine was deployed across a wide
range of Mitsubishi, Dodge, Plymouth, and Colt-branded vehicles throughout the
1980s and into the early 1990s.
Mitsubishi Starion / Chrysler Conquest: The G54B ECI-Turbo served as the
exclusive powertrain for this rear-wheel-drive turbocharged coupe, with output
varying by market and model year. The widebody variants received intercooled
versions producing up to 175 HP (130 kW).
Mitsubishi Mighty Max / Dodge D-50 / Plymouth Arrow Truck: The G54B was offered
as the premium engine option in compact pickup trucks, available in both
naturally aspirated and turbocharged configurations depending on market and trim
level.
Mitsubishi Montero / Pajero (L044, L045): First-generation SUVs utilized the
G54B in naturally aspirated form, valued for its low-end torque characteristics
suited to off-road applications.
Mitsubishi Sapporo / Dodge Challenger / Plymouth Sapporo: The rear-wheel-drive
coupe and sedan platforms received the G54B in both carbureted and fuel-injected
variants across various model years.
Mitsubishi Sigma / Galant Sigma: The executive sedan and wagon variants employed
the G54B as the top-displacement engine option, often paired with automatic
transmissions.
Mitsubishi Cordia / Tredia: The front-wheel-drive coupe and sedan platforms
utilized the G54B in naturally aspirated form in certain markets.
Dodge Raider: The Mitsubishi Montero rebadged for the North American market
utilized the G54B as its gasoline powertrain offering.
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