2g Astron II

From Mitsipedia
Second Generation Astron II combustion chambers
Rocker gear on the Second Generation Astron II
Second Generation Astron II dished pistons

The second generation Astron II was fitted to fuel-injected TR and TS models.

The revised Astron II included "kidney shaped" combustion chambers in the cylinder head, roller rockers, dished top pistons and the self-adjusting balance shaft chain adjusting mechanism fitted to late model Astron IIs.

The quickest way to identify the second generation Astron II from the original is to look for a knock sensor under the injection plant. First generation Astron IIs do not even have a hole for it. Other methods are by it's engine number (prefixed by W531, W532) or by the casting number on the head. Second generation heads are marked "M9".

As a result of these modifications the compression ratio raised to 9.2:1 and power rose to 98kW @ 4750 rpm (103 kW if ran on premium unleaded thanks to the knock sensor included as part of the engine management system). Torque also rose to 212Nm @ 3750 rpm.

Technical Specifications

Type In line 4 cylinder overhead cam with counter balance shafts. Transversely mounted
Displacement 2555cc (2.6 litres)
Bore 91.1mm
Stroke 98mm
Maximum oversize 1.00mm
Compression Ratio 9.2:1
Firing Order 1,3,4,2
Power Output (EFI) 98 kW @ 4750 rpm (103kW when running PULP), 212 Nm @ 3750 rpm
Type Alluminum Alloy with hemispherical combustion chambers and crossflow design
Inlet Valve Diameter 46.00mm
Exhaust Valve Diameter 38.00mm
Valve Face Angle 45 º
Valve Clearance Maintained by hydraulic lash adjusters
Inlet Opens 25º BTDC
Inlet Closes 61º ABDC
Inlet Duration 266º
Exhaust Opens 66º BBDC
Exhaust Closes 20º ABDC
Exhaust Duration 266º
Overlap 45º
Inlet Cam Lobe Height 42.50mm
Exhaust Cam Lobe Height 42.56mm
Nominal Cam Lift 10.50mm
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