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Mitsubishi 4A30 Specifications
| Engine Model: Mitsubishi 4A30 |
| Engine Type: 4-cycle inline 4-cylinder SOHC or DOHC liquid-cooled gasoline |
| Total Displacement: 40.2 cu.in (0.66 L) |
| Rated Engine Power: 38-52 Hp (28-38 kW) at 7200 rpm |
| Fuel System Type: Multi-point electronic fuel injection |
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| General Technical Data |
The Mitsubishi 4A30 is a 0.66-liter inline-four gasoline engine belonging to Mitsubishi’s A-engine family, designed for use in the company’s kei-class vehicles during the 1990s and early 2000s. Introduced in 1993, the 4A30 replaced the earlier 3G83 three-cylinder unit in some applications, offering improved smoothness, refinement, and power potential through its four-cylinder configuration.
The engine was developed to meet Japan’s kei
car displacement limit of 660 cc while delivering high efficiency, low
emissions, and reliable operation under the demanding conditions of city
driving. Two naturally aspirated variants were produced: a Single
Overhead Camshaft (SOHC) 16-valve version emphasizing torque and
economy, and a Double Overhead Camshaft (DOHC) 16-valve version tuned
for higher output and smoother high-speed performance.
Constructed with Mitsubishi’s signature engineering focus on compactness
and efficiency, the 4A30 combined aluminum cylinder head design, modern
electronic fuel injection, and lightweight internals. Its robust
cast-iron cylinder block provided exceptional durability and allowed for
precise thermal control and low vibration. The engine featured a
perfectly square geometry, offering balanced characteristics between
low-end torque and high-revving response.
With its small displacement, it was primarily
installed in kei passenger cars such as the Mitsubishi Minica, Toppo,
and Pajero Mini, where reliability, fuel economy, and serviceability
were paramount. Over its production run, the 4A30 became recognized for
its simplicity, long life, and adaptability to emissions regulations
without major redesigns.
The Mitsubishi 4A30 engine has a total displacement of 659 cc (0.659
liters or 40.2 cubic inches), achieved through a bore of 60.0 mm (2.36
inches) and a stroke of 58.3 mm (2.30 inches). This near-square
configuration provides a balanced compromise between torque and
smoothness, enabling responsive acceleration for lightweight vehicles.
The compression ratio for the naturally
aspirated SOHC version is approximately 9.5:1, while the DOHC variant
typically employs a slightly higher ratio around 10.0:1 for improved
efficiency and power output. Both versions operate on the four-stroke
Otto cycle, with a firing order of 1-3-4-2. The crankshaft rotates
clockwise viewed from the flywheel end.
The cylinder block is cast iron, offering rigidity and superior wear
resistance within the kei displacement constraints. The head is aluminum
alloy, with integrated camshaft carriers and cross-flow port arrangement
to optimize intake and exhaust gas flow. The pistons are aluminum alloy
with three rings - two compression and one oil control ring - while the
connecting rods are forged steel.
The crankshaft runs on five main bearings to
ensure excellent balance and reduced vibration. The valve actuation
system differs between the two major variants: the SOHC employs a single
camshaft operating sixteen valves via rocker arms, while the DOHC
version uses twin camshafts directly operating the valves through bucket
tappets. Both designs utilize four valves per cylinder (two intake, two
exhaust) to enhance breathing efficiency and reduce pumping losses.
Power output for the SOHC version ranges between 38 and 42 Hp (28 to 31
kW, or 37 to 41 bhp) at around 7,000 revolutions per minute. Maximum
torque is approximately 55 to 57 Nm (40 to 42 lb-ft) at 5,000 rpm. The
DOHC version achieves slightly higher performance figures, producing 50
to 52 Hp (37 to 38 kW, or 49 to 51 bhp) at 7,500 rpm and torque of 60 Nm
(44 lb-ft) at 5,500 rpm. The redline is approximately 8,000 rpm for the
DOHC engine and 7,000 rpm for the SOHC. Idle speed is electronically
controlled at 850 ± 50 rpm.
| Fuel System |
The 4A30 employs a multipoint electronic fuel injection (EFI) system designed to ensure precise fuel delivery under all operating conditions. An in-tank electric fuel pump delivers fuel through a high-pressure line to the fuel rail, where solenoid injectors meter fuel into each intake port.
The injectors are controlled by the electronic control unit (ECU), which receives input from the throttle position sensor, manifold absolute pressure sensor, crank angle sensor, and oxygen sensor. The fuel pressure regulator maintains a constant differential pressure of about 300 kPa (43 psi). The system returns excess fuel to the tank through a dedicated return line.
Fuel used is regular unleaded gasoline with an octane rating of 91 RON or higher. The throttle body is cable-operated and incorporates an idle air control valve for stable idling. The air filter is a dry paper element housed in a plastic air box, replaced every 20,000 km (12,000 miles).
| Lubrication System |
A fully pressurized wet-sump lubrication system ensures reliable oil distribution to all moving components. A trochoid-type oil pump, driven by the crankshaft, draws oil from the sump through a mesh strainer and delivers it to the main oil gallery. Oil is then distributed to the crankshaft bearings, connecting rods, camshafts, and valve train components.
The engine incorporates oil jets directed at the underside of each piston for cooling and improved detonation resistance. The system operates with an oil pressure of approximately 350 to 400 kPa (50 to 58 psi) at 3,000 rpm. The total oil capacity including filter change is about 2.8 liters (3.0 US quarts, 2.5 Imperial quarts).
Recommended oil viscosity is SAE 5W-30 or 10W-30 meeting API SJ or higher specification. The oil filter is a replaceable spin-on cartridge mounted on the right side of the block. Oil and filter replacement intervals are 10,000 km (6,000 miles) or every six months under normal service.
| Cooling System |
The 4A30 uses a liquid-cooled system with forced circulation. A belt-driven centrifugal water pump circulates coolant through the engine block, cylinder head, radiator, and heater core. The thermostat begins to open at approximately 82 C (180°F) and is fully open by 95°C (203°F). A pressurized aluminum radiator with plastic end tanks provides efficient heat dissipation, assisted by an electric fan controlled by the ECU based on coolant temperature.
Total coolant capacity is approximately 3.5 liters (3.7 US quarts, 3.1 Imperial quarts). The system operates at a pressure of 88 kPa (13 psi) and uses a 50/50 mixture of ethylene glycol antifreeze and distilled water, offering freeze protection to about –35°C (–31°F). Coolant replacement interval is every 40,000 km (25,000 miles) or two years.
| Intake and Exhaust Systems |
The intake manifold is cast aluminum on early engines and plastic composite on later versions to reduce heat transfer and weight. Its runner lengths are tuned for mid-range torque, optimizing drivability at low vehicle speeds. The throttle body is located at the front of the intake plenum and includes an idle air bypass.
The exhaust manifold is a compact cast-iron design, merging the four outlets into a single downpipe connected to a catalytic converter located close to the engine for fast light-off. The muffler system is tuned for quiet operation, in line with kei car refinement requirements. Some later versions include an EGR (Exhaust Gas Recirculation) valve for NOx reduction.
| Ignition and Electrical System |
The ignition system employs a transistorized distributorless ignition system (DIS) with dual ignition coils firing pairs of cylinders simultaneously (waste-spark system). The ECU controls ignition advance based on engine speed, load, and temperature. Spark plugs are nickel or platinum-tipped, specified as NGK BKR6E or equivalent, gapped to 1.0 mm (0.039 inches).
Spark plug replacement is recommended every 30,000 km (18,000 miles). The alternator is rated at 65 amperes, and the starter motor output is approximately 0.8 kW. The electrical system operates at 12 volts DC.
| Valve Timing and Drive Mechanism |
The camshaft(s) are driven by a toothed rubber timing belt from the crankshaft. On the SOHC engine, the belt directly drives the single camshaft, while on the DOHC variant, it drives the exhaust camshaft, which in turn drives the intake camshaft through a short chain or gear coupling. Belt tension is maintained by an automatic spring-loaded tensioner.
Timing belt replacement interval is 100,000 km (62,000 miles). Valve clearance adjustment is manual, using screw-and-locknut tappets on the SOHC engine and shim-over-bucket lifters on the DOHC version. Standard valve clearances (cold) are approximately 0.15 mm (0.006 inches) for intake and 0.25 mm (0.010 inches) for exhaust valves.
| Dimensions and Weight |
The overall length of the 4A30 engine is approximately 580 mm (22.8 inches), width 520 mm (20.5 inches), and height 620 mm (24.4 inches). The dry weight of the complete engine assembly is around 85 kg (187 lbs) for the SOHC version and about 90 kg (198 lbs) for the DOHC version. Compact dimensions and light weight make it suitable for transverse installation in front-wheel-drive kei cars. Engine mounts are rubber-isolated to minimize vibration transmission to the chassis.
| Maintenance Data |
0Recommended intervals are as follows: engine oil and filter every 10,000 km (6,000 miles), air filter every 20,000 km (12,000 miles), spark plugs every 30,000 km (18,000 miles), and coolant every two years. Valve clearance inspection should be performed every 40,000 km (25,000 miles). The timing belt and tensioner should be replaced every 100,000 km (62,000 miles).
Idle speed and ignition timing are electronically controlled and require no routine adjustment. Compression pressure in each cylinder should measure approximately 1,200 kPa (174 psi) at cranking speed, with a minimum limit of 1,000 kPa (145 psi). Maximum allowable difference between cylinders is 100 kPa (15 psi).
| Tightening Torques |
Cylinder head bolts: first stage 25 Nm (18 lb-ft), second stage 50 Nm
(37 lb-ft), then tighten an additional 90 degrees.
Main bearing cap bolts: 38 Nm (28 lb-ft).
Connecting rod bolts: 30 Nm (22 lb-ft) plus 90 degrees.
Camshaft bearing cap bolts: 12 Nm (9 lb-ft).
Crankshaft pulley bolt: 140 Nm (103 lb-ft).
Flywheel bolts: 75 Nm (55 lb-ft) plus 90 degrees.
Spark plugs: 20 Nm (15 lb-ft).
Oil drain plug: 40 Nm (30 lb-ft).
Intake manifold bolts: 22 Nm (16 lb-ft).
Exhaust manifold nuts: 30 Nm (22 lb-ft).
Valve cover bolts: 8 Nm (6 lb-ft).
| Vehicle Applications |
The Mitsubishi 4A30 engine powered several kei-class and compact models, particularly throughout the 1990s and early 2000s. Key applications include the Mitsubishi Minica (H31A–H42A series, 1993–2002), Mitsubishi Toppo and Toppo BJ, Mitsubishi Bravo microvan, and the early Mitsubishi Pajero Mini (H51A–H58A).
It was also used in the Mitsubishi Town Box and some variants of the Minica Dangan. The engine’s compactness, smoothness, and reliability made it ideal for these light vehicles designed for urban use. Production continued until the early 2000s when the engine was succeeded by more advanced kei-class units meeting newer emission regulations, including the 3G83 and 3B20 series engines.
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