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Mitsubishi Astron engine
Mitsubishi Astron engine
Mitsubishi Astron engine
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Mitsubishi Astron engine
Mitsubishi G54B engine
Overview
ManufacturerMitsubishi Motors
Also called4G5/4D5
Production1972–2023
Layout
ConfigurationFour-cylinder
Displacement1.9–2.6 L (1,850–2,555 cc)
Cylinder bore84 mm (3.31 in)
88 mm (3.46 in)
91.1 mm (3.59 in)
Piston stroke90 mm (3.54 in)
95 mm (3.74 in)
98 mm (3.86 in)
Cylinder block materialCast-iron[1]
Cylinder head materialaluminium[1]
Valvetrain
  • SOHC 2 valves x cyl.
  • DOHC 4 valves x cyl.
Compression ratio8.8:1-21.0:1
Combustion
TurbochargerTD04, TD05 or TF035HL2 variable geometry with intercooler (on some versions)
Fuel systemCarburetor
Multi-point fuel injection
Throttle-body fuel injection
Indirect injection
Common rail Direct Injection
Fuel typeGasoline, Diesel
Cooling systemWater-cooled
Output
Power output46–178 PS (34–131 kW)
Torque output137–400 N⋅m (101–295 lb⋅ft)
Chronology
SuccessorSirius 4G64 (Gasoline engine)

The Mitsubishi Astron or 4G5/4D5 engine, is a series of straight-four internal combustion engines first built by Mitsubishi Motors in 1972. Engine displacement ranged from 1.8 to 2.6 litres, making it one of the largest four-cylinder engines of its time.

Design

[edit]

It employed a hemispherical cylinder head, chain-driven single overhead camshaft (SOHC) and eight valves (two per cylinder). United States passenger car versions had a small secondary intake valve referred to as the "Jet Valve". This valve induced swirl in the intake charge, enabling the use of leaner fuel/air mixtures for lower emissions. It was designed as a cartridge containing the valve spring and seat which simply screwed into a threaded hole in the head, similar to a spark plug but inside the cam cover. The rocker arms for the intake valve were widened on the valve end to accommodate the cartridge, which was equipped with a very soft valve spring in order to avoid wear on the camshaft intake lobe. Modifications to the head were thereby reduced as the Jet Valve negated the necessity for a three-valve-per-cylinder design.[2]

In 1975, the Astron 80 introduced a system dubbed "Silent Shaft": the first use of twin balance shafts in a modern engine. It followed the designs of Frederick Lanchester, whose original patents Mitsubishi had obtained, and proved influential as Fiat/Lancia, Saab and Porsche all licensed this technology.

The 4D5 engine is a range of four-cylinder belt-driven overhead camshaft diesel engines which were part of the "Astron" family, and introduced in 1980 in the then new fifth generation Galant. As the first turbodiesel to be offered in a Japanese passenger car, it proved popular in the emerging SUV and minivan markets where Mitsubishi was highly successful, until superseded by the 4M4 range in 1993. However, production of the 4D5 (4D56) continued throughout the 1990s as a lower-cost option than the more modern powerplants. Until now it is still in production, but made into a modern powerplant by putting a common rail direct injection fuel system into the engine.

4G51 (1.85 liters)

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The 4G51 displaces 1.9 L (1,850 cc).

Applications:

4G52 (2.0 liters)

[edit]

The 4G52 displaces 2.0 L (1,995 cc). Peak power for a 1975 Canter is 100 PS (74 kW), but power increased to as much as 125 PS (92 kW) for the twin-carb version fitted to the Galant GTO GSR and A115 Galant GS-II.

Used an 84 mm × 90 mm (3.31 in × 3.54 in) bore and stroke. In Australia this engine was used in the Sigma, Scorpion and L200.

Applications:

4G53 (2.4 liters)

[edit]

The SOHC eight-valve 4G53 displaces 2.4 L (2,384 cc), with bore & stroke at 88 mm × 98 mm (3.46 in × 3.86 in). Peak power is 110 PS (81 kW) at 5000 rpm,[4] as fitted to the Rosa bus or the Canter cabover truck. This engine shares its dimensions with the contemporary Fuso 4DR1 diesel engine.

Applications

4G54 (2.6 liters)

[edit]

The SOHC eight-valve 4G54 (also known as the G54B) displaces 2.6 L (2,555 cc), with bore & stroke at 91.1 mm × 98 mm (3.59 in × 3.86 in). The G54B for the US market had a cylinder head with additional jet valves to improve emissions (MCA-Jet system). The engine was fitted to various Mitsubishi models from 1978 to 1997 and to the American Chrysler K-cars and their derivatives between 1981 and 1987. It was primarily set up longitudinally for use in rear-wheel drive and all-wheel drive platforms but also as a transverse engine in the front-wheel drive platform of the Mitsubishi Magna and Chrysler K platform. Chrysler commonly marketed the engine "Hemi," whereas the Australian-made version was marketed as the "Astron II" and featured "Balance Shaft" technology, which was subsequently licensed to Porsche and other automakers. The original engine featured a Mikuni two-barrel carburetor with a secondary vacuum actuator; later versions adopted EFI. Chrysler commonly paired this engine with its A470 3-speed automatic transmission; in Australia, Mitsubishi adapted it to a 5-speed manual transmission and its "ELC" (Electronic Control) 4-speed automatic transmission, featuring electronic overdrive. Chrysler eventually replaced the 4G54 with its own 2.5 L engine, whereas Mitsubishi replaced it with a 2.4 L engine codenamed 4G64.

Specifications:

ECI-Multi

[edit]

Multi-point fuel injection

  • 98 kW (131 hp) at 4750 rpm (91 RON)
  • 102 kW (137 hp) at 4750 rpm (95 RON)
  • 212 N⋅m (156 lb⋅ft) at 3750 rpm (91 RON)
  • 220 N⋅m (162 lb⋅ft) at 4000 rpm (95 RON)
  • Compression ratio: 9.2:1

Carburetor

[edit]

Single two-Venturi downdraught carburetor. 85 kW (114 hp) at 5000 rpm (91 RON), 198 N⋅m (146 lb⋅ft) at 3000 rpm (91 RON). Compression ratio: 8.8:1

Applications:

4G55 (2.3 liters)

[edit]

The 4G55 displaces 2.3 L (2,346 cc).

4D55 (2.3 liters diesel)

[edit]

Displacement - 2.3 L (2,346 cc)
Bore x Stroke - 91.1 mm × 90 mm (3.59 in × 3.54 in)
Fuel Type - Diesel
Valves per cylinder - 2[7][8][9]

Non-Turbo

[edit]
  • Power - 55 kW (75 PS) at 4200 rpm (JIS)[10]
48 kW (65 hp) at 4200 rpm (SAE)
  • Torque - 147 N⋅m (108 lb⋅ft) at 2500 rpm (JIS)
137 N⋅m (101 lb⋅ft) at 2000 rpm (SAE)

Turbo (TC05 non-wastegated turbo)

[edit]
  • Power - 60 kW (80 hp) at 4000 rpm (SAE)
  • Torque - 169 N⋅m (125 lb⋅ft) at 2000 rpm (SAE)
  • Engine type - Inline 4-cylinder SOHC
  • Compression ratio - 21.0:1 (384 psi (26.5 bar))[11]
  • Applications - 1980-1983

Turbo (TD04 wastegated turbo)

[edit]
  • Power - 70 kW (95 PS) at 4200 rpm (JIS)[10]
62 kW (84 PS) at 4200 rpm (DIN)[10]
64 kW (86 hp) at 4200 rpm (SAE)
  • Torque - 181 N⋅m (133 lb⋅ft) at 2500 rpm (JIS)
175 N⋅m (129 lb⋅ft) at 2500 rpm (DIN)
182 N⋅m (134 lb⋅ft) at 2000 rpm (SAE)

4D56 (2.5 liters diesel)

[edit]
Turbocharged and intercooled 4D56 engine in a 1991 Mitsubishi Pajero

Displacement - 2.5 L (2,477 cc)
Bore x Stroke - 91.1 mm × 95 mm (3.59 in × 3.74 in)
Fuel type - DIESEL

This engine is also built by Hyundai in South Korea, meaning it also sees use in some products made by their Kia subsidiary. Hyundai calls it the D4BA/D4BX (normally aspirated), D4BF (non-intercooled turbo), or D4BH (intercooled turbo).

Non-Turbo

[edit]
  • Power - 74 hp (55 kW) at 4200 rpm
  • Torque - 105 lb⋅ft (142 N⋅m) at 2500 rpm
  • Engine type - Inline 4-cylinder SOHC
  • Fuel system - Distribution type jet pump
  • Compression ratio - 21.0:1

Non-intercooled Turbo

[edit]
  • Power - 84 PS (62 kW) at 4200 rpm[12]
  • Torque - 148 lb⋅ft (201 N⋅m) at 2000 rpm
  • Engine type - Inline 4-cylinder SOHC

Intercooled Turbo (TD04 Turbo)

[edit]
  • Power - 90 hp (67 kW) at 4200 rpm
  • Torque - 145 lb⋅ft (197 N⋅m) at 2000 rpm
  • Engine type - Inline 4-cylinder SOHC
  • Fuel system - Distribution type jet pump
  • Compression ratio - 21.0:1[13]

Intercooled Turbo (TD04 water-cooled Turbo)

[edit]
  • Power - 99 hp (74 kW) at 4300 rpm
  • Torque - 177 lb⋅ft (240 N⋅m) at 2000 rpm
  • Engine type - Inline 4-cylinder SOHC
  • Rocker arm - Roller Follower type[14]
  • Fuel system - Distribution type jet pump (indirect injection)
  • Combustion chamber - Swirl type
  • Bore x Stroke - 91.1 mm × 95 mm (3.59 in × 3.74 in)
  • Compression ratio - 21.0:1
  • Lubrication System - Pressure feed, full flow filtration
  • Intercooler Type - Aluminium Air-to-Air, Top-mounted
  • Turbocharger - Mitsubishi TD04-09B

Also known as Hyundai D4BH[15]

Intercooled Turbo TF035HL2 (1st Generation DI-D)

[edit]
  • Power - 114 PS (84 kW) at 4000 rpm
  • Torque - 182 lb⋅ft (247 N⋅m) at 2000 rpm
  • Engine type - Inline 4-cylinder
  • Fuel system - 1st Generation Common Rail Direct Injection (CRDi)
  • Compression ratio - 17.0:1[13][16][17]

Intercooled Turbo (2nd Generation DI-D)

[edit]
  • Power - 136 PS (100 kW) at 4000 rpm
  • Torque - 236 lb⋅ft (320 N⋅m) at 2000 rpm.
  • Engine type - Inline 4-cylinder DOHC 16 valve
  • Fuel system - 2nd Generation Common Rail Direct Injection (CRDi)
  • Compression ratio - 17.0:1[13][16][17][18]
  • application: Mitsubishi Challenger, Mitsubishi Triton

Intercooled Turbo (3rd Generation DI-D with variable geometry turbo)

[edit]
  • Power - 178 PS (131 kW) at 4000 rpm[19]
  • Torque - Manual transmission: 295 lb⋅ft (400 N⋅m) at 2000 rpm[19]
- Automatic transmission: 258 lb⋅ft (350 N⋅m) at 1800 rpm[19]

See also

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Mitsubishi Astron engine

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from Grokipedia
The Mitsubishi Astron engine is a family of straight-four internal combustion engines produced by from 1972 to the present, with diesel variants continuing into the 2020s, renowned for its inline-four configuration, single overhead design, and innovative Silent Shaft system to minimize . Developed by as part of the company's expanding automobile division, the Astron series—designated under the 4G5 codes for variants and 4D5 for diesels—was engineered to power a wide range of rear-wheel-drive and later front-wheel-drive vehicles, marking a significant advancement in Japanese automotive engineering during the 1970s oil crisis era. The engines featured a cast-iron block paired with an aluminum and hemispherical combustion chambers, enabling displacements from 1.8 liters to 2.6 liters in the lineup, with the flagship 4G54 model offering 2,555 cc (2.6 L) via a bore of 91.1 mm and stroke of 98 mm. This modular design allowed for both carbureted and fuel-injected configurations, as well as turbocharged and intercooled variants in performance applications, with power outputs typically ranging from 74 kW (100 hp) in base models to over 131 kW (178 hp) in high-output versions. A standout feature was the patented Silent Shaft counterbalance system, licensed from Frederick W. Lanchester's earlier designs and also adopted by , which used dual shafts to counteract second-order vibrations inherent in four-cylinder engines, improving smoothness without sacrificing the compact inline layout. The Astron was the first Japanese passenger car engine to comply with the stringent U.S. federal emissions standards, incorporating innovations like the Mitsubishi Jet valve—a third auxiliary valve per cylinder—to enhance and reduce emissions. Diesel iterations, such as the 4D55, provided robust for trucks and vans, further extending the family's versatility. Applications spanned passenger cars, sports coupes, and light trucks globally, including the , Colt, Starion, and Lancer; Dodge and Plymouth models like the , Challenger, and Ram 50 pickup; and even specialized uses such as U.S. presidential limousines and industrial forklifts. Production longevity—over 50 years as of 2025—reflected its durability and adaptability, with aftermarket support remaining strong today due to the engine's overbuilt internals, including nitrided crankshafts and piston oil squirters in later variants.

Overview

History and Development

The Mitsubishi Astron engine family, designated as the 4G5 series, was introduced in as a new generation of water-cooled, inline-four engines featuring a single overhead (SOHC) design. This marked a significant advancement over Mitsubishi's prior OHV engines, such as the E-series, providing improved efficiency and performance for passenger vehicles amid the emerging focus on fuel economy following the . Development of the Astron emphasized balance and refinement, incorporating patented twin balance shafts—derived from Frederick W. Lanchester's earlier concept—to reduce vibrations inherent in larger four-cylinder configurations, a technology later licensed to . The initial 2.0-liter 4G52 variant debuted in 1973 with the Galant GTO coupé, expanding the lineup to include displacements from 1.8 to 2.6 liters for various rear-wheel-drive models like the Galant and Colt. Key evolutions included the turbocharged 4G54 in 1982 for the Starion sports coupe, enhancing power output while maintaining the core architecture, and the diesel counterpart, the 4D55, which debuted in 1983 for the Mighty Max pickup truck. Under the longstanding Mitsubishi-Chrysler partnership, the 2.6-liter 4G54 was supplied for Chrysler's K-car platform vehicles, such as the Dodge Aries and , from 1981 to 1987, bolstering Chrysler's lineup during its recovery period. Production of the Astron family spanned from 1972 into the late 1990s, with gasoline variants phased out by the mid-1990s in favor of newer designs like the Sirius series, while diesel versions of the 4D55 continued in commercial applications such as the Pajero and Delica until around 1997. This long service life underscored the engine's durability and adaptability across global markets.

General Specifications

The Mitsubishi Astron engine family, designated as the 4G5 series for variants and 4D5 series for diesel variants, consists of inline-four engines with a shared architecture featuring a cast-iron block and aluminum alloy . These water-cooled designs employ a single overhead (SOHC) valvetrain driven by a timing belt, with two valves per and a configuration. Common dimensions across the family include a bore range of 81 to 91 mm and of 90 to 98 mm, yielding total displacements from 1.8 L to 2.6 L. Compression ratios typically fall between 8.5:1 and 9.5:1 for engines, while diesel variants operate at 21:1 to 23:1 to support their indirect injection systems. Diesel-specific components in the 4D5 series include a vortex chamber system and higher compression for efficient operation, while maintaining the core SOHC layout and liquid cooling of the gasoline counterparts. Early 4G5 models, introduced in 1972, complied with Japanese emission standards, with subsequent adaptations in later variants to meet U.S. federal regulations and emerging European norms as the engines were exported globally.

Design Features

Core Architecture

The Mitsubishi Astron engine series features a robust inline-four architecture designed for both gasoline and diesel applications, with a focus on durability and efficiency in mid-size vehicles. The engine employs a cast-iron cylinder block paired with an aluminum cylinder head, providing structural rigidity while minimizing weight. This combination supports displacements ranging from 1.8 to 2.6 liters in gasoline variants and 2.3 to 2.5 liters in diesels, enabling modular adaptations between fuel types through shared block designs and interchangeable components. The utilizes a single overhead (SOHC) driven by a timing , operating two s per via rocker arms for efficient actuation and improved compared to earlier pushrod designs. Early models incorporate mechanical lifters, while later iterations introduce hydraulic self-adjusting lifters to minimize and maintenance needs. Early emissions-compliant models feature the MCA-Jet , which includes a third auxiliary intake per to promote swirl and enhance for reduced emissions. The design promotes cross-flow intake and exhaust paths, with hemispherical chambers enhancing airflow and efficiency in configurations. Internally, the engine relies on a forged crankshaft supported by five main bearings for balanced operation, with applied in high-output turbocharged versions to enhance durability under stress. Aluminum pistons are standard, contributing to reduced reciprocating mass, and the series integrates twin balance shafts—known as the "Silent Shaft" system—to counteract second-order vibrations inherent in four-cylinder layouts, marking a pioneering mass-production implementation of this technology. Cooling is managed by a belt-driven water pump, while lubrication employs a full-pressure system with an oil pump chain-driven off the , ensuring consistent oil delivery to critical components. High-output variants include piston-cooling oil jets that spray oil onto the underside of the pistons to mitigate heat buildup and support sustained performance. These elements collectively underscore the Astron's engineering emphasis on reliability and adaptability, influencing subsequent powertrains and even licensing agreements for technology.

Fuel and Induction Systems

The Mitsubishi Astron gasoline engines initially relied on carbureted fuel delivery systems, with early models featuring downdraft carburetors from suppliers like Mikuni in two-barrel configurations for displacements of 2.0 liters and larger, enabling balanced -air mixing for reliable performance in applications such as the Chrysler-powered of the . In the , Mitsubishi introduced electronic fuel injection (ECI) across the Astron lineup to enhance efficiency and emissions compliance, with the ECI-Multi system debuting on the 4G54 engine in like the TN Magna series. This multi-point injection setup utilized an in-tank electric delivering regulated of approximately 196 kPa, a disposable 10-micron , and four injectors (16 ± 3 ohms resistance) mounted on a , all controlled by a ECU that adjusted delivery based on inputs from sensors including air flow, position, temperature, and oxygen levels for optimized . For the diesel variants, the 4D55 and early 4D56 engines employed via a pre-chamber , where was injected into a small auxiliary chamber connected to the main to promote smoother ignition and reduced noise in these SOHC eight-valve configurations. Later iterations of the 4D56 in the late transitioned to direct injection (DI-D) with a DOHC 16-valve setup, injecting straight into the main using a distributor-type mechanical pump for superior fuel atomization, power output, and economy, as seen in models like the 1999 Pajero. Induction systems in the Astron series were predominantly naturally aspirated, but turbocharging became available starting in 1980 to boost performance, with gasoline models like the 4G54 utilizing TC05 or TD04 turbos in rally-derived applications for increased without significant displacement changes. Diesel engines such as the 4D55T and 4D56T paired turbochargers like the TD04 with intercoolers for enhanced low-end response in trucks and SUVs. Emissions control evolved with the adoption of three-way catalytic converters on gasoline Astron engines from 1981 onward, replacing earlier two-way units to simultaneously reduce hydrocarbons, , and through oxidation and reduction reactions in compliance with tightening regulations. Diesel models incorporated (EGR) systems on later 4D56 variants to lower emissions by recirculating inert exhaust gases into the intake, mitigating combustion temperatures while maintaining durability in off-road use.

Gasoline Engines

4G51

The 4G51 is the entry-level gasoline engine in the Astron series, featuring a displacement of 1.85 (1,855 cc) achieved through an inline-four configuration with a bore of 81 mm and a stroke of 90 mm. It employs a single overhead (SOHC) architecture shared across the Astron family, optimized for efficient operation in compact vehicles. Equipped solely with carburetion for fuel delivery, the 4G51 delivered power outputs ranging from 90 to 105 hp (67–78 kW) at around 4,200–5,000 rpm, paired with torque figures of 140–152 Nm, emphasizing economical performance over high output. Introduced in 1973 and produced through 1985, with primary applications starting in 1975 models, this engine found primary application in (JDM) economy models like the Galant and Sigma, where its compact dimensions contributed to improved and vehicle handling. The 4G51's construction, weighing approximately 120 kg in base form, suited it particularly for front-wheel-drive economy cars, with no turbocharged variants developed to maintain simplicity and cost-effectiveness. Renowned for its robust cast-iron block and aluminum head that supported high-mileage durability—often exceeding 200,000 km with routine servicing—the engine nonetheless required vigilant timing belt maintenance to prevent failures from belt wear or stretching.

4G52

The 4G52 is a 2.0-liter inline-four from Mitsubishi's Astron series, serving as a versatile mid-range powerplant for various passenger vehicles and light commercial applications. With a displacement of 1,995 cc, it features a bore of 84 mm and a of 90 mm, contributing to its balanced performance characteristics suitable for sedans and coupes. Produced from 1973 to 1986, the 4G52 was initially introduced in the Galant GTO in January 1973 as Mitsubishi's 2.0-liter offering, emphasizing reliability and efficiency in the post-oil crisis era. Power outputs ranged from 100 to 125 hp at 5,000–5,500 rpm, paired with 165–175 Nm of torque at around 3,000–4,000 rpm, depending on the market and tuning. Early versions relied on induction for simplicity and cost-effectiveness, while later variants in select models adopted early electronic to improve drivability and emissions compliance, aligning with evolving technologies in Mitsubishi's lineup. A key innovation in the 4G52 was the incorporation of balance shafts, branded as the "silent shaft" system, which counteracted second-order vibrations inherent in inline-four designs to deliver smoother operation comparable to larger V8 engines. Some configurations featured the optional MCA-Jet , a system that enhanced by promoting stratified charge combustion and reducing emissions through precise air-fuel mixing. This made the engine particularly adaptable for emissions-regulated markets, achieving highway fuel economy of approximately 25 in sedan applications like the Galant and . The 4G52 found widespread use in balanced setups for mid-size sedans such as the and , as well as coupes, providing adequate power for daily driving without excessive fuel consumption. In the US market, it powered exported models including the Ram 50 and pickup trucks from 1979 to around 1982, where it delivered about 93 hp in detuned form to meet federal standards. Its role as a mid-range option distinguished it from larger siblings like the 4G53, prioritizing versatility over high-output performance for compact to mid-size vehicles.
SpecificationDetails
Displacement1,995 cc
Bore × Stroke84 mm × 90 mm
Power Range100–125 hp @ 5,000–5,500 rpm
Torque Range165–175 Nm @ 3,000–4,000 rpm
Induction Variants; early EFI in select models
Production Period1973–1986

4G53

The 4G53 is the 2.4-liter variant of the Mitsubishi Astron engine series, serving as a transitional design between the earlier 4G52 and the later 4G54. With a displacement of 2,384 cc achieved through a bore of 88 mm and a of 98 mm, it featured a block and aluminum SOHC 8-valve head, emphasizing durability for light-duty applications. This configuration provided a balance of power and suitable for SUVs and trucks, outputting between 95 and 110 hp at 4,500–5,000 rpm and 172–200 Nm of , primarily via a carbureted induction system. Introduced in August 1974 as part of the Astron lineup, the 4G53 entered full production around 1975 and continued until 1998, though its primary use in passenger vehicles and exports tapered off after 1986. It was largely confined to Asian markets, particularly where it powered the Jeep J-series SUVs, with limited availability in Australian models like the Galant and Canter. The 4G53's unique features included a larger bore and increased stroke compared to the 4G52, enhancing low-end for better off-road while sharing core components like the and block architecture but with reinforced internals for higher stress. It incorporated technology to mitigate vibrations inherent in four-cylinder designs. Reliability-wise, the 4G53 offered a of approximately 400,000 km with proper , though it lacked hydraulic lifters requiring periodic adjustments and demanded timing checks after 250,000 km. Common issues included malfunctions and overheating related to or problems, particularly in demanding or hot operating conditions.

4G54

The 4G54, also known as the G54B in export markets, is a 2.6-liter inline-four from Mitsubishi's Astron family, featuring a single overhead (SOHC) design with an initial eight-valve configuration. It has a displacement of 2,555 cc, achieved through a bore of 91.1 mm and a stroke of 98 mm, paired with a cast-iron block and aluminum for durability and heat dissipation. Produced from 1980 to 1997, this became Mitsubishi's most widely exported variant, powering models like the Starion and Mighty Max , where its robust construction suited both performance and utility applications. Naturally aspirated versions of the 4G54 delivered power outputs ranging from 112 to 140 hp, depending on market-specific tuning and emissions standards, with typically between 188 and 220 Nm. Turbocharged iterations marked a significant advancement; the eight-valve 4G54T produced up to 162 hp at 5,200 rpm and 265 Nm of , while later 12-valve updates in models like the intercooled Starion ESI-R boosted output to 197 hp. The engine's reinforced block and internals were specifically engineered to handle boost pressures, enabling reliable operation under without major modifications. This made the 4G54 Mitsubishi's first turbocharged four-cylinder engine in a production passenger car, debuting in the 1982 Starion and setting a benchmark for affordable turbo in the . Fuel systems evolved across the production run to meet varying regulatory and performance demands. Base models used a carbureted setup for simplicity and cost-effectiveness, while from 1983 onward, the ECI-Multi multi-point fuel injection (MPI) system was introduced on higher-output variants, improving efficiency and throttle response. Turbocharged models incorporated electronic fuel injection with intercoolers for enhanced charge cooling and power delivery, contributing to the engine's versatility in both domestic and export applications. Variants included the G54B for international markets, often with adaptations for local fuels, and the JDM-specific G54C, which featured refined tuning for Japanese emissions and performance norms.

4G55

The 4G55 is a 2.3-liter inline-four from Mitsubishi's Astron family, featuring a displacement of 2,346 cc with a bore of 91.1 mm and stroke of 90 mm. It was produced from 1983 to 1988, primarily for Southeast Asian markets where it powered vans and trucks such as the Delica L300 bus variants. This variant was designed with a shortened stroke compared to the 4G54 for improved rev range and economy-oriented tuning, making it suitable for commercial applications rather than high-performance use. Power outputs ranged from 115 to 130 hp at 5,000 rpm, with torque between 170 and 190 Nm, available in both carbureted and electronic fuel injection configurations that shared technology with other Astron engines. The 4G55 exhibited fewer reliability issues than its turbocharged siblings in the family, benefiting from simpler tuning, though limited parts availability poses challenges for modern maintenance and aftermarket support.

Diesel Engines

4D55

The 4D55 is a 2.3-liter inline-four developed as part of the Astron family, featuring a displacement of 2,346 cc achieved through a bore of 91.1 mm and a stroke of 90 mm. Produced from 1980 to 1986, it was primarily installed in vehicles such as the Pajero and Delica , where it provided reliable low-end for off-road and utility applications. The engine employs with pre-chamber combustion to promote efficient swirl and complete burning of fuel, contributing to its durability in demanding conditions. The base non-turbo variant delivers 65-75 hp at 4,200 rpm and 142 Nm of , suitable for economical operation in lighter-duty models. Introduced in the early , the non-wastegated TC05 turbocharged version increased output to 80 hp and 160-170 Nm, offering improved performance without advanced boost control for simpler tuning in export markets like the U.S. Dodge Ram 50 pickup. From 1986 onward, the wastegated TD04 turbo variant enhanced throttle response and power delivery, achieving 84-95 hp while maintaining in the 190 Nm range for better drivability in the Pajero and Delica. Key to the 4D55's longevity is its cast-iron cylinder head, which provides superior thermal stability and resistance to cracking under the high compression ratios typical of diesel engines (around 21:1). The SOHC eight-valve design and robust block support the engine's reputation for enduring high-mileage use in rugged environments, though common issues include head gasket failures in high-mileage examples without proper maintenance. Aftermarket support remains available for tuning and parts. It relies on basic indirect injection systems detailed in broader Astron diesel architecture.

4D56

The 4D56 is a 2.5-liter (2477 cc) inline-four featuring a bore of 91.1 mm and a stroke of 95 mm, designed as part of the Astron family for enhanced durability in light trucks and SUVs. Introduced in May 1986 as Japan's first passenger car diesel with a , it marked a significant step in 's diesel technology, evolving from to advanced direct injection systems over its production run, which extended until 2016 in various markets. The engine's longevity stemmed from its robust cast-iron block and progressive upgrades, making it a staple in models like the L200 pickup and Pajero , where it powered global sales through the and . The 4D56's variants reflect its extensive evolution to meet emissions standards and performance demands. The base non-turbo version, used primarily in early applications, delivered 70-80 hp, prioritizing and reliability over power. The initial turbo variant in 1986 was non-intercooled, boosting output to 85-94 hp while maintaining the indirect injection system for simpler maintenance. Subsequent intercooled models with the TD04 , featuring air- or water-cooling for better charge air density, achieved 99-125 hp, improving delivery for off-road use in vehicles like the Pajero. From 1999 onward, the introduction of direct injection diesel (DI-D) generations with common-rail fuel systems revolutionized the 4D56's performance and efficiency. The first-generation DI-D, equipped with the intercooled TF035HL2 turbo, produced 114 hp, with a reduced of 17:1 to accommodate higher pressures. The second generation refined this to around 136-160 hp, enhancing low-end torque through optimized injectors. By the , the third-generation variant integrated a variable geometry turbo (VGT) for superior spool-up and emissions control, yielding up to 178 hp, as seen in later L200 models. Unique to later iterations, the 4D56 adopted an aluminum in the 1990s to reduce weight and improve heat dissipation, aiding in higher power outputs without compromising longevity. Late models from the mid-2000s incorporated a (DPF) to comply with Euro 4 standards, trapping soot particles and regenerating via active fuel dosing, which extended its viability in emissions-regulated regions until production ceased. Common reliability concerns include timing belt failures if not replaced regularly, but the engine is noted for durability exceeding 300,000 km with proper care.
VariantKey FeaturesPower Output (hp)Torque (Nm)Introduction Period
Non-Turbo, SOHC 8-valve70-80142 @ 2500 rpm1986
Non-Intercooled TurboFixed geometry turbo, 85-94201 @ 2000 rpm1986
Intercooled TD04 TurboAir/water , SOHC99-125240-294 @ 2000 rpmLate 1980s
1st Gen DI-D (TF035HL2)Common-rail direct injection, DOHC 16-valve114247 @ 2000 rpm1999
2nd Gen DI-DRefined common-rail, 136-160320 @ 2000 rpmEarly 2000s
3rd Gen VGTVariable geometry turbo, DPF integration, aluminum head175-178380-400 @ 2000 rpmMid-2000s

Applications and Legacy

Vehicle Applications

The Mitsubishi Astron engine family powered a wide range of vehicles produced by Mitsubishi and its partners, spanning passenger cars, SUVs, MPVs, and commercial models from the late 1970s through the early 2000s.

Passenger Cars

The 4G52 variant was fitted to the from 1977 to 1980, providing a reliable powerplant for this rear-wheel-drive sedan. Later, the models in the 1980s utilized both the 4G52 and 4G54 engines, with the latter offering greater displacement for improved performance in mid-size sedans and s. The turbocharged 4G54 powered the sporty from 1982 to 1990, emphasizing high-revving capabilities in a rear-wheel-drive .

SUVs and MPVs

Astron diesel engines were prominent in Mitsubishi's off-road lineup, with the 4D55 installed in the Pajero from 1982 to 1986 and the Delica during the 1980s, marking early adoption of turbo-diesel technology in compact and vans. The 4D56 succeeded it in the Pajero, serving from 1986 to 2006 across multiple generations, and also appeared in the Delica from 1986 to 1999. The gasoline 4G54 was used in the Pajero from 1982 to 1992, bridging fuel options for this iconic . Badge-engineered versions included the , a turbo 4G54-equipped rebadged Starion sold from 1983 to 1989 in .

Commercial Vehicles

The 4D56 diesel engine drove the Mitsubishi L200 Triton pickup from 1996 to 2008, supporting its role in global markets for light-duty hauling. Earlier, the 4G54 powered the (Mitsubishi's L200 export name) and its Ram 50 counterpart from 1982 to 1996, providing durable propulsion for compact trucks.

Export Specifics

In the US market, the 4G54 was integrated into K-car platforms, such as the Aries from 1981 to 1987, as part of Chrysler's partnership with for efficient front-wheel-drive compacts. The 4G52 and 4G54 engines were also used in the and from 1979 to 1983. Australian models like the featured the 4G54 in early transverse front-wheel-drive configurations during the 1980s. Overall, the Astron engines equipped over 20 distinct models and variants through Mitsubishi, Chrysler, and other partners, contributing to the brand's expansion in diverse global segments. Specialized applications included powering U.S. presidential limousines during the Reagan administration and industrial forklifts.

Performance and Aftermarket Use

The turbocharged variant of the 4G54 engine, as fitted in vehicles like the Starion ESI-R, delivered solid stock performance for a 1980s sports coupe, with 0-60 mph acceleration times around 7 seconds and a quarter-mile in 15.3 seconds, thanks to its 188 horsepower and responsive turbo setup. The 4D56 diesel engine, commonly used in off-road models such as the Pajero, provided robust low-end torque ideal for demanding terrain, with stock figures of approximately 179 Nm at 2,000 rpm enabling strong pulling power in applications like towing and trail driving. Aftermarket modifications have extended the 4G54's potential significantly, with popular upgrades including larger turbochargers like the TD05-18G, which can support over horsepower when paired with fuel system enhancements and ECU tuning, appealing to enthusiasts seeking higher output without major internal changes. swaps featuring the 4G54 into custom hot rods and older trucks are common due to its compact size and rear-wheel-drive compatibility, often integrated with modern transmissions for improved drivability. The 4D56 benefits from straightforward tuning via increased boost and fuel delivery, pushing beyond 390 Nm in off-road builds for enhanced low-speed grunt. In racing history, the 4G54-powered Starion participated in 1980s rallies under regulations through prototypes developed by , though the category's end limited its competitive runs; these efforts laid groundwork for Mitsubishi's later rally successes. The 4D56 diesel featured in Pajero entries that secured multiple victories in the and , contributing to the model's 12 overall wins as the most successful vehicle in the event's history, thanks to its durability in extreme desert conditions. Modern enthusiast support remains strong, with dedicated online communities discussing G54B (4G54) rebuilds and tuning strategies on forums like Sigma-Galant.com, where members share guides for EFI conversions and performance mods. Aftermarket parts availability persists into 2024, including turbo upgrades and overhaul kits from suppliers like Kinugawa and Mace Engineering, alongside video tuning resources on platforms like for ongoing maintenance. Despite its tunability, the 4G54 faces age-related challenges in high-boost applications, such as limited revving beyond 4,800 rpm without head porting and potential oil pump failures after 200,000 km, necessitating reinforced internals for sustained power gains. The carbureted 4D56 variants pose emissions hurdles for contemporary street use, often requiring retrofits or ECU remaps to comply with modern standards, while both engines demand vigilant cooling to prevent issues in hot climates.

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