Mitsubishi G33B Specifications
| Engine Model: Mitsubishi G33B |
| Engine Type: 4-cycle inline 4-cylinder SOHC 8-valve liquid-cooled gasoline |
| Total Displacement: 87.8 cu.in (1.44 L) |
| Rated Engine Power: 80-82 Hp (60-61 kW) at 5500 rpm |
| Fuel System Type: Carburetor |
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The Mitsubishi G33B is a 1.4-liter inline four-cylinder
gasoline engine produced from the late 1970s through the early 1980s as a member
of the Saturn engine family, designated internally as the 4G3 series. This
engine family, which also included the 1.2-liter G32B and the 1.6-liter G62B,
represented Mitsubishi’s response to the growing demand for fuel-efficient yet
durable powerplants in the post-1973 oil crisis era.
The G33B was positioned as a mid-range displacement option, offering greater
torque than the 1.2-liter variant while maintaining reasonable fuel consumption
suitable for compact passenger cars and light commercial vehicles. A defining
feature of this engine, particularly in its later iterations, was the MCA-Jet
(Mitsubishi Clean Air) system, which incorporated an auxiliary jet valve into
each cylinder to induce swirl in the incoming air-fuel mixture, enabling more
complete combustion and reduced emissions without the requirement for complex
electronic controls.
The engine’s architecture is characterized by its cast iron cylinder block,
aluminum cylinder head, and single overhead camshaft driven by a rubber timing
belt - a configuration that was advanced for its era in this displacement class.
The G33B engine exemplifies Mitsubishi’s engineering approach during the
transition period from carbureted engines to the electronically managed systems
that would follow in the late 1980s. Its design prioritizes mechanical
simplicity, serviceability, and durability over high specific output. The
engine’s 73.0 mm bore and 86.0 mm stroke yield an undersquare configuration that
favors low-end torque generation - a characteristic well-suited to urban driving
and light commercial applications where sustained low-speed pulling power is
valued.
The SOHC valvetrain operates two conventional valves per cylinder plus, on
MCA-Jet variants, an additional small jet valve adjacent to the intake valve.
This jet valve system, a Mitsubishi innovation, introduces a secondary stream of
air-fuel mixture that creates turbulence within the combustion chamber,
improving flame propagation and reducing hydrocarbon and carbon monoxide
emissions to meet the increasingly stringent emissions standards of the late
1970s. The engine utilizes a downdraft carburetor for fuel delivery, with the
specific carburetor model varying by market and emissions requirements.
The timing belt-driven camshaft arrangement reduces mechanical noise compared to
chain-driven designs but introduces a critical maintenance interval, as the G33B
is an interference engine where timing belt failure results in valve-to-piston
contact and significant engine damage. The engine’s reputation within vintage
Mitsubishi circles is one of dependability, with well-maintained units capable
of high mileage, though age-related issues such as carburetor wear, vacuum
leaks, and deterioration of the MCA-Jet system components are common in
surviving examples.
Production Period: 1977-1983.
Engine Code: G33B (4G33 in later designation).
Configuration: Inline four-cylinder (I4).
Displacement: 1,439 cc (87.8 cu.in).
Bore: 73.0 mm (2.87 in).
Stroke: 86.0 mm (3.39 in).
Firing Order: 1-3-4-2.
Compression Ratio: 9.0:1.
Combustion System: Carbureted, with MCA-Jet auxiliary valve system.
Aspiration: Naturally aspirated.
Maximum Engine Speed: 6,000 rpm.
Maximum Power: 80-82 hp (60-61 kW) @ 5,500 rpm.
Maximum Torque: 87-89 lb-ft (118-121 Nm) @ 3,500 rpm.
The G33B cylinder block is manufactured from cast iron,
utilizing a deep-skirt design that extends below the crankshaft centerline to
provide rigidity and reduce vibration transmission to the vehicle structure. The
block features a conventional open-deck design at the top of the cylinder bores.
Five main bearings support the crankshaft, with the bearing caps secured using
high-tensile steel bolts. The cylinder bores are cast directly into the block
and are finished with a precision-honed surface.
The block incorporates the mounting provisions for the oil pump on the front
cover and the water pump on the side. Cast-in coolant passages surround each
cylinder bore, while oil galleries are drilled into the block to supply
pressurized lubricant to the crankshaft, connecting rods, and cylinder head. The
engine mounting points are cast into the block to accommodate transverse or
longitudinal orientations depending on the vehicle application. The block also
includes provisions for the mechanical fuel pump, which is mounted on the side
and actuated by an eccentric lobe on the camshaft.
The cylinder head is manufactured from cast aluminum
alloy, featuring a cross-flow design with intake ports on one side and exhaust
ports on the opposite side. The single overhead camshaft is driven by a timing
belt at the front of the engine and operates the valves via rocker arms with
adjustable screw-and-locknut mechanisms. The valvetrain consists of two
conventional valves per cylinder - one intake and one exhaust - with the
addition of a smaller jet valve adjacent to the intake valve on MCA-Jet
variants.
The jet valve is actuated by a dedicated rocker arm from the same camshaft lobe
that operates the main intake valve, introducing a secondary charge that
promotes swirl within the combustion chamber. Valve clearances are adjustable
and require periodic maintenance; the specified cold clearances are 0.15 mm
(0.006 in) for the intake valves, 0.25 mm (0.010 in) for the exhaust valves, and
0.25 mm (0.010 in) for the jet valves. The valve diameters are approximately
38.0 mm (1.50 in) for the intake valves and 33.0 mm (1.30 in) for the exhaust
valves, with the jet valve having a significantly smaller diameter.
The fuel system utilizes a downdraft carburetor mounted
above the intake manifold, with the specific carburetor model varying by market,
emissions requirements, and vehicle application. Common carburetor types include
the Mikuni-Solex two-barrel unit or a single-barrel unit on lower-specification
models. The carburetor incorporates an automatic choke system, usually
thermostatic or electric-assisted depending on the model year, to provide proper
fuel enrichment during cold starts. A mechanical fuel pump mounted on the
cylinder block draws fuel from the tank and delivers it to the carburetor float
chamber.
The MCA-Jet system draws its air-fuel mixture from a dedicated circuit within
the carburetor, delivering it through separate passages to the jet valves. The
intake manifold is constructed from aluminum and is designed to distribute the
air-fuel mixture evenly to each cylinder while providing the necessary passages
for the MCA-Jet secondary circuit. A vacuum advance mechanism connected to the
carburetor base provides ignition timing adjustment based on engine load.
The lubrication system employs a wet-sump design with a
gear-type oil pump mounted within the front timing cover, driven directly by the
crankshaft. The pump draws oil from the sump through a screened pickup tube and
delivers it through a full-flow spin-on oil filter mounted on the cylinder
block. The filtered oil is distributed through internal galleries to the
crankshaft main bearings, connecting rod bearings, camshaft bearings, and the
rocker arm assembly.
An oil pressure relief valve is integrated into the oil pump assembly to
maintain consistent pressure and prevent over-pressurization at higher engine
speeds. The rocker arm shaft receives oil through a vertical passage from the
cylinder head gallery, with oil flowing through the rocker arms to lubricate the
valve stem tips and pivot points. Total system capacity, including the filter,
is approximately 3.5 liters (3.7 qt).
The cooling system is a pressurized water-cooled design
utilizing a crossflow or downflow radiator depending on the vehicle platform. A
centrifugal water pump, driven by the timing belt, circulates coolant through
the cylinder block, cylinder head, and radiator. The water pump is a service
item replaced in conjunction with the timing belt. A wax-element thermostat is
positioned in the coolant outlet housing, with a nominal opening temperature of
82°C (180°F) for most applications. The system incorporates an expansion tank or
overflow reservoir to accommodate coolant expansion and to facilitate air
removal.
An engine-driven mechanical fan, often with a viscous clutch on
higher-specification models, provides airflow across the radiator. The cooling
system is designed to maintain consistent operating temperatures across varying
load conditions, with the cast iron block and aluminum head combination
requiring proper coolant maintenance to prevent galvanic corrosion. Coolant
capacity varies by vehicle application but generally ranges from 5.0 to 6.0
liters (5.3 to 6.3 qt).
Intake System: The intake system consists of an air
cleaner housing with a replaceable dry-type filter element, ducting to the
carburetor, and the aluminum intake manifold. The air cleaner incorporates a
thermostatic air intake system on many variants, drawing warm air from a stove
on the exhaust manifold during cold operation to improve driveability and reduce
carburetor icing.
Exhaust System: The exhaust system utilizes a cast iron exhaust manifold, which
on MCA-Jet variants is designed to work in conjunction with the air injection
system for emissions control. The exhaust gases are directed through a single
exhaust pipe to a silencer. Some market variants incorporate a catalytic
converter in the exhaust system to meet local emissions regulations.
Ignition System: The ignition system utilizes a distributor with mechanical and
vacuum advance mechanisms. The distributor is driven by the rear of the intake
camshaft and houses the ignition points or, on later variants, a magnetic pickup
for electronic ignition. The ignition coil is mounted remotely. The spark plug
specification is NGK BP6ES or BPR6ES for resistor-type plugs, with a spark plug
gap set to 0.7-0.8 mm (0.028-0.031 in).
Electrical System: The engine is equipped with a 12-volt electrical system. The
starter motor is a direct-drive type mounted to the transmission bellhousing or
the cylinder block depending on the vehicle application. The alternator is
belt-driven from the crankshaft pulley and provides charging current for the
battery and vehicle electrical loads. Early variants may utilize a DC generator
rather than an alternator.
Emissions Control: The MCA-Jet system is complemented by additional emissions
control components including an exhaust gas recirculation (EGR) valve, a
crankcase ventilation system, and in some markets, a catalytic converter. The
system is calibrated to meet the emissions standards applicable at the time of
manufacture.
Overall Length: 610 mm (24.0 in)
Overall Width: 560 mm (22.0 in)
Overall Height: 650 mm (25.6 in)
Dry Weight (complete engine): 125 kg (276 lbs)
Engine Oil: SAE 10W-30, 10W-40, or 20W-50 meeting API
SF, SG, or higher classification. Oil Capacity (with filter change): 3.5 L (3.7
qt). Oil Change Interval: 5,000 km (3,100 mi) or 6 months under normal
conditions. Timing Belt Replacement Interval: 100,000 km (60,000 mi) for
interference engine; failure results in valve damage.
Fuel Filter: Replace at 20,000 km (12,400 mi) intervals. Coolant Capacity:
5.0-6.0 L (5.3-6.3 qt) depending on vehicle platform. Coolant Specification:
Ethylene glycol-based antifreeze with corrosion inhibitors; replace every 2
years or 40,000 km (24,800 mi).
Valve Clearance (Cold): Intake: 0.15 mm (0.006 in); Exhaust: 0.25 mm (0.010 in);
Jet Valve: 0.25 mm (0.010 in). Engine Idle Speed: 700-800 rpm (with MCA-Jet
system properly adjusted). Compression Pressure: Standard: 1.2-1.4 MPa (174-203
psi); Minimum service limit: 0.9 MPa (131 psi).
Connecting Rod Cap Bolts: 40-45 Nm (30-33 lb-ft)
Main Bearing Cap Bolts: 50-55 Nm (37-41 lb-ft)
Cylinder Head Bolts, Stage 1: 30 Nm (22 lb-ft)
Cylinder Head Bolts, Stage 2: 60 Nm (44 lb-ft)
Camshaft Bearing Caps: 20-25 Nm (15-18 lb-ft)
Intake Manifold to Cylinder Head: 15-20 Nm (11-15 lb-ft)
Exhaust Manifold to Cylinder Head: 20-25 Nm (15-18 lb-ft)
Flywheel/Flexplate to Crankshaft: 90-100 Nm (66-74 lb-ft)
Spark Plugs: 20-25 Nm (15-18 lb-ft)
Rocker Arm Shaft Brackets: 20-25 Nm (15-18 lb-ft)
Oil Pump Mounting: 10-12 Nm (7-9 lb-ft)
Mitsubishi Lancer (A140 series / Lancer EX, 1977-1983).
Mitsubishi Mirage / Colt (A150 series, 1978-1983).
Mitsubishi Celeste (A140 series, 1978-1981).
Mitsubishi Galant (A120 series, 1977-1980).
Mitsubishi Delica / L300 (early L-series vans, 1979-1983).
Mitsubishi L200 (early pickup models, selected markets).
Dodge Colt (North America).
Plymouth Champ (North America).
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