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Neptune (4G4x)
1.2L 4G42 in a Lancer A71
Manufacturer Mitsubishi Motors
Production 1971-1979
Configuration Inline 4
Cylinder block alloy Cast Iron
Valvetrain Overhead Valve
Predecessor JH4
Successor Orion (4G1x)

The Neptune (or 4G4x) family of engines were a family of inline 4 cylinder engines featuring cast iron blocks, alloy heads and are of a overhead valve (pushrod) design. They were produced from 1971 through 1979.

The Neptune family replaced the JH4 which Mitsubishi had been building under licence from Willy's. The engine was shortlived, with it unable to meet increasingly tougher emissions regulations in the 1970s, leading to it being replaced by the Orion.


The 4G41 is a 1.4 Litre engine displacing 1378cc with a 76.5mm x 75.0mm bore and stroke. It has a compression ratio of 9.0:1. It was available with a single barrel Stromberg carburetor producing 63 kW at 6000rpm and 115 Nm at 4000rpm and a double barrel Stromberg carburetor producing 70 kW at 6300rpm and 121 Nm at 4500rpm. It saw service in non-Australian Galant FTO, Delicas and in FG14 forklifts.


The 4G42 is a 1.2 Litre engine displacing 1187cc with a 71.0mm x 75.0mm bore and stroke. Using a compression ratio of 9.0:1, it produced 51 kW at 6000rpm and 95 Nm at 4000rpm. It saw service in non-Australian A71 model Lancers.

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