The Mitsubishi G64B is a 2,555 cc, inline‑six naturally aspirated petrol engine produced between 1986 and 1995. It features a single overhead camshaft (SOHC), 12 valves, and a carburettor or throttle — body fuel injection depending on market and year. In standard form it delivered 92–103 kW (125–140 PS) with torque figures between 192–210 Nm, offering smooth linear power delivery ideal for executive cruising.
Fitted to models such as the Debonair (A33A), Proudia (D — 01)…
Production years 1986–1989 meet pre‑Euro standards; 1990–1995 models may comply with Euro 1 depending on market (JAMA Type Approval #JAMA/EMS/2031).
The Mitsubishi G64B is a 2,555 cc inline‑six naturally aspirated petrol engine engineered for executive sedans (1986–1995). It combines SOHC architecture with either carburettor or throttle-body injection to deliver smooth, vibration-free power. Designed to meet pre‑Euro and early Euro 1 standards, it prioritizes refinement over emissions sophistication.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,555 cc | |
Fuel type | Petrol (Unleaded) | |
Configuration | Inline‑6, SOHC, 12‑valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 85.0 mm × 75.0 mm | |
Power output | 92–103 kW (125–140 PS) @ 5,000–5,500 rpm | |
Torque | 192–210 Nm @ 3,500–4,000 rpm | |
Fuel system | Carburettor or throttle-body injection (TBI) | |
Emissions standard | Pre‑Euro (1986–1989); Euro 1 (1990–1995, market‑dependent) | |
Compression ratio | 8.8:1 | |
Cooling system | Water‑cooled | |
Turbocharger | None | |
Timing system | Chain (maintenance‑free design) | |
Oil type | API SF/SG, SAE 10W‑40 | |
Dry weight | 158 kg |
The Mitsubishi G64B was used across Mitsubishi's A33A/D-01 platforms with longitudinal mounting and no external licensing. This engine received platform-specific adaptations—reinforced mounts in the Debonair and modified accessory brackets in the Proudia—and from 1990 the updated Galant Σ adopted throttle-body injection replacing carburettors, creating minor interchange limits. All adaptations are documented in OEM technical bulletins.
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The G64B's primary reliability risk is distributor drive gear wear in early carburetted builds, with elevated incidence in high‑temperature or high‑load urban use. Mitsubishi internal quality reports from 1989 indicated a notable share of pre‑1990 engines requiring ignition system repair before 120,000 km, while JAMA durability audits flagged marginal drive train robustness in initial batches. Extended oil intervals and poor coolant maintenance accelerate timing chain and head gasket issues, making fluid service adherence critical.
Analysis derived from Mitsubishi technical bulletins (1987–1993) and JAMA failure statistics (1990–1998). Repair procedures should follow manufacturer guidelines.
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The G64B is mechanically smooth and durable when maintained, but early carburetted models (1986–1989) had distributor drive gear issues. Post-1990 revisions improved ignition reliability. Regular oil changes with correct 10W-40 oil are essential for longevity, especially in hot climates.
Key issues include distributor drive gear wear (pre-1990 carburetted), timing chain tensioner wear, carburettor jet clogging, and head gasket failure under thermal stress. These are documented in Mitsubishi TSB‑ME‑87‑005 and related service communications. Most are preventable with scheduled maintenance.
The G64B powered the Debonair (A33A, 1986–1992), Proudia (D-01, 1991–1995), and Galant Σ (E39A, 1986–1989). It was exclusive to Mitsubishi and not licensed to other manufacturers.
Limited tuning potential due to SOHC 12V design and low compression. Carburettor jetting or TBI recalibration can yield modest gains (~5–8 kW), but risks lean conditions. Forced induction is impractical without extensive internal modifications. Most owners prioritize refinement over performance.
Moderate for an inline-six. In a 1988 Debonair 2.6 GL, typical consumption is ~11.5 L/100km (city) and ~8.2 L/100km (highway), or about 25 mpg UK combined. Real-world mixed driving typically returns 22–28 mpg (UK), depending on carburettor condition and driving style.
No. The G64B is a non-interference engine. If the timing chain were to fail, piston-to-valve contact would not occur, minimizing internal damage risk. However, chain replacement is still recommended at 150,000 km as a preventive measure.
Mitsubishi specifies SAE 10W-40 oil meeting API SF or SG standards. Modern API SN oils are acceptable. Always use high-quality mineral oil and change it every 7,500 km to protect the timing chain and valvetrain.
Comprehensive technical documentation and regulatory references
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EU emissions and type-approval regulations (e.g., CELEX:32007R0715, CELEX:32017R1151).
GOV.UK: Vehicle Approval & V5C
UK vehicle approval processes, import rules, and MoT guidance.
DVLA: Engine Changes & MoT
Official guidance on engine swaps and inspection implications.
Vehicle Certification Agency (VCA)
UK type-approval authority for automotive products.
Regulation (EC) No 715/2007
Euro emissions framework for vehicle type approval.
Commission Regulation (EU) 2017/1151
WLTP and RDE testing procedures for emissions certification.
GOV.UK: Vehicle Approval
UK compliance and certification requirements for imported and modified vehicles.
VCA Certification Portal
Type-approval guidance and documentation.
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