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Astron (4G5x)
Manufacturer Mitsubishi Motors
Configuration Inline 4
Cylinder block alloy Cast Iron
Cylinder head alloy Aluminum alloy
Valvetrain SOHC (except for a DOHC race version)
Successor Astron II (2.6L)

Mitsubishi debuted the Astron engine in 1972 and over its lifetime ranged in capacity from 1.85 to 2.6 litres. It was the first mass produced engine to feature twin counter-rotating balance shafts (dubbed Silent Shaft by Mitsubishi), which were used to dampen rocking and vertical forces in the interest of smoothness.

The engine featured "hemispherical" combustion chambers and 2 valves per cylinder in overhead cam configuration. It was designed for use in rear-wheel and four-wheel drive vehicles. The Astron has been used in passenger and commercial vehicles, forklifts and even marine applications. It has also been built in both petrol and diesel forms.


A 1.85 Litre Petrol engine with a displacement of 1855cc. It used a 81.0x90.0mm bore and stroke and was used in early Galants and Sigmas.


A 2.0 Litre petrol engine with a displacement of 1995cc. It used a 84.0x90.0mm bore and stroke.

In Australia this engine was used in the Sigma, Scorpion, L200 and L300.

4G52 Turbo

In 1981, Mitsubishi produced a limited edition GH Sigma Turbo. The turbocharged Sigma was powered by a 4G52 with Garrett T3 turbocharger producing 8psi boost, Zenith CD175 carburetor and a lower compression ratio of 7.3:1. The engine produced 116 kW and 235Nm of torque. It has the distinction of being the first Australian produced turbocharged engine.


A petrol 2.4 Litre engine with a displacement of 2384cc. Using a 88.0x98.0mm bore and stroke it was used in the Challenger and Canter.


A 2.6 Litre (2555cc) petrol engine which came in two variants. A standard compression (8.2:1) version and a high compression (9.5:1) version. It uses a 91.1x98.0mm bore and stroke.

In Australia, the standard compression version was used in GH-GK Sigma, Scorpion, Canter, Express, Pajero, Triton and Mazda B2600 (Ford Courier). The high compression version was used in some GK and GN Sigmas.

This engine became the basis for the Astron II used in the Magna.

3 cylinder
3A9x 3A90 3A91 3A92
4 cylinder
Neptune 4G41 4G42
Orion 4G11 4G12 4G13 4G15 4G17 4G18 4G19 G4ED
Sirius 4G61 4G62 4G63 4G64 4G67 4G69
Astron 4G51 4G52 4G53 4G54
Astron II Original Revised
Saturn 4G30 4G31 4G32 4G33 4G37
4G9x 4G91 4G92 4G93 4G94
4A9x 4A90 4A91 4A92
4B1x 4B10 4B11 4B11T 4B12
Inline 6
Saturn 6 6G34
6G7x 6G71 6G72 SOHC 12v 6G72 SOHC 24v 6G72 DOHC Early 6G74 Late 6G74 Ralliart 6G74 6G75
6A1x 6A10 6A11 6A12 6A13
6B3x 6B31
8A80 8A80