Astron II

From Mitsipedia
Astron II
1g efi engine.jpg
Astron II in a first generation Magna
Overview
Manufacturer Mitsubishi Motors Australia Limited
Also called 4G54, 4G54B, G54B
Production 1985 - 1996
Layout
Configuration In-line 4
Displacement 2555cc
Cylinder block alloy Cast Iron
Cylinder head alloy Aluminum Alloy
Valvetrain SOHC
Chronology
Predecessor Astron
Successor Sirius

The Astron II was an improved version of the original Astron and debuted in the mid 1980s. It was available only in 2.6 Litre form.

The Astron II's main difference over its predecessor were in the cylinder head with hemispherical style combustion chambers, larger exhaust and inlet valves and hydraulic lash adjusters. The pistons were flat topped with compression rising to 8.8:1 (up from 8.2:1) to produce 83 kW at 5200 rpm and 200 Nm at 2400 rpm (up from 76kW at 4800rpm and 192 Nm at 2400 rpm) in carburetted form.

The 2.6 Litre engine was praised for being powerful, economical and refined.

Original Astron II

The Original Astron II was fitted to the all First Generation Magnas (TM-TP), carburetted Second Generation Magnas (TR-TS), the GN Sigma, Triton ME through MJ and Pajero NE through NH.

When used in the Magna, these engines typically had the numbers M1 through M5 cast into the head and V5xx engine numbers.

Technical Specifications

Type In line 4 cylinder overhead cam with counter balance shafts
Displacement 2555cc (2.6 litres)
Bore 91.1mm
Stroke 98mm
Maximum oversize 1.00mm
Compression Ratio 8.8:1
Firing Order 1,3,4,2
Power output (Carby) 83 kW @ 5200 rpm, 200Nm @ 2400 rpm
Power Output (EFI) 93 kW @ 4800 rpm, 205 Nm @ 2400 rpm
HEAD SPECIFICATIONS
Type Alluminum Alloy with hemispherical combustion chambers and crossflow design
Port Diameter 40.00mm
Inlet Valve Diameter 46.00mm
Exhaust Valve Diameter 38.00mm
Valve Face Angle 45 º
Valve Clearance Maintained by hydraulic lash adjusters
CAMSHAFT SPECIFICATIONS
Inlet Opens 25º BTDC
Inlet Closes 59º ABDC
Inlet Duration 264º
Exhaust Opens 64º BBDC
Exhaust Closes 20º ATDC
Exhaust Duration 264º
Overlap 45º
Inlet Cam Lobe Height 42.50mm
Exhaust Cam Lobe Height 42.56mm
Nominal Cam Lift 10.50mm

Revised Astron II

Revised Astron II combustion chambers used in the TS Magna (M9 Head)
Rocker gear on the revised Astron II
Astron II dished pistons used in the TS Magna (M9 Head)

A revised Astron II was fitted to fuel-injected TR and TS models. The revised Astron II used roller rockers, a higher compression ratio (9.2:1 up from 8.8:1), larger inlet ports (42mm up from 40mm in the original), a knock sensor and a self-adjusting balance shaft chain adjusting mechanism as fitted to late model original Astron IIs.

These changes increased power to 98 kW at 4750 rpm (103 kW when running on premium unleaded) and torque rose to 212 Nm at 3750 rpm.

Revised Astrons can be identified by their knock sensor situated under the fuel injection plant (original Astron II's do not even have a hole for it), its engine number (all are prefixed by W531 or W532) or the casting number on the head (M6 through M9). The M6 and M7 were used in the TR Magna.

With the release of the TS Magna, the Astron II was modified once again with a switch to the M8 and M9 head which used swirl-type "kidney shaped" combustion chambers with dished top pistons (to match the combustion chambers). These promoted better mixing of air and fuel, less detonation (knocking) and a better flame front.

The M6 through M7 head is said to be the best Astron II head - using the largest valves, ports and having good flow characteristics. The M9 head while similar has less desirable flow through the intake ports due to the shape of the combustion chamber.

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
HEAD SPECIFICATIONS
Type Aluminum Alloy with hemispherical combustion chambers and crossflow design
Inlet Port Diameter 42.00 mm
Inlet Valve Diameter 46.00mm
Exhaust Port Diameter 40.00mm
Exhaust Valve Diameter 38.00mm
Valve Face Angle 45 º
Valve Clearance Maintained by hydraulic lash adjusters
CAMSHAFT SPECIFICATIONS
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
MITSUBISHI PETROL ENGINES
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
V6
6G7x 6G71 6G72 SOHC 12v 6G72 SOHC 24v 6G72 DOHC Early 6G74 Late 6G74 Ralliart 6G74 6G75
6A1x 6A10 6A11 6A12 6A13
6B3x 6B31
V8
8A80 8A80