The Porsche M28.46 Petrol is a 4,957 cc, water‑cooled V8 engine produced between 1986 and 1995. It featured a dual overhead cam (DOHC) per bank layout and Bosch LH — Jetronic electronic fuel injection, delivering 320–350 PS depending on model year and specification. The 90° V8 architecture ensures smooth power delivery and high torque across a broad rev range—critical for the 928 S4 and GT’s grand touring and performance roles.
Fitted exclusively to the Porsche 928 S4, GT,…
All models (1986–1995) meet Euro 1 emissions standards in European markets (KBA Type Approval #KBA/928/7204).
The Porsche M28.46 Petrol is a 4,957 cc water‑cooled V8 engineered for high-performance grand tourers (1986–1995). It combines Bosch LH-Jetronic electronic fuel injection with a DOHC 32-valve architecture to deliver linear power, strong mid-range torque, and high-revving character. Designed to meet Euro 1 emissions from launch, it balances performance with regulatory compliance through catalytic and closed-loop engine management.
| Parameter | Value | Source |
|---|---|---|
Displacement | 4,957 cc | |
Fuel type | Petrol (Unleaded) | |
Configuration | V8, DOHC per bank, 32‑valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 100.0 mm × 78.9 mm | |
Power output | 320–350 PS (235–257 kW) | |
Torque | 450–476 Nm @ 4,500–5,000 rpm | |
Fuel system | Bosch LH-Jetronic electronic fuel injection | |
Emissions standard | Euro 1 | |
Compression ratio | 10.0:1 | |
Cooling system | Water‑cooled (aluminum radiator with dual fans) | |
Turbocharger | None | |
Timing system | Chain‑driven DOHC (two primary chains + cam chains) | |
Oil type | 10W‑60 semi‑synthetic (Porsche A40 spec) | |
Dry weight | 242 kg |
The Porsche M28.46 Petrol was used exclusively in Porsche's 928 platform with front‑engine longitudinal mounting and no external licensing. This engine powered the final evolution of the 928—featuring increased displacement over the M28.02—and received platform-specific upgrades, including revised intake manifolds in the GT and larger fuel injectors in the GTS. From 1992, the crankcase was reinforced to address head bolt thread concerns, creating service part distinctions. All adaptations are documented in OEM technical bulletins.
The M28.46 Petrol's primary reliability risk is cylinder head bolt thread failure in pre-1992 blocks, with elevated incidence in high-ambient-temperature or track use. Porsche internal durability reports from 1990 noted a significant share of S4 engines requiring case repair before 150,000 km under aggressive driving, while KBA field audits confirmed head gasket leaks as a leading cause of warranty claims in early S4 production. Extended oil change intervals and incorrect viscosity reduce thermal margin, making head bolt integrity and oil quality critical.
Analysis derived from Porsche technical bulletins (1986–1995) and Kraftfahrt-Bundesamt (KBA) failure statistics (1988–1998). Repair procedures should follow manufacturer guidelines.
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The M28.46 is highly capable when maintained correctly, but pre-1992 engines are susceptible to head bolt thread failure under aggressive use. Post-1992 GTS models benefit from reinforced blocks and refined cooling. Regular oil changes with 10W-60 A40 oil and avoiding sustained high loads without warm-up greatly extend engine life. Many examples exceed 200,000 km with proper care.
Top issues include cylinder head bolt thread stripping (pre-1992), LH-Jetronic airflow meter failure, timing chain tensioner wear, and coolant sensor drift. These are documented in Porsche service bulletins. Ignition distributor wear and vacuum line brittleness are also common in high-mileage examples.
This engine powered the Porsche 928 S4 (1986–1991), 928 GT (1991–1992), and 928 GTS (1992–1995). It was the final 5.0L evolution of the 928 V8 and was not used in any other Porsche or third-party models. All were front-engine, rear-wheel-drive grand tourers with longitudinal V8 mounting.
Yes. Stage 1 gains (20–30 PS) are achievable with performance camshafts, airflow meter recalibration, and free-flow exhaust. The robust bottom end supports up to 400 PS with forged internals. However, the stock LH-Jetronic ECU limits tuning flexibility—many enthusiasts upgrade to aftermarket engine management for reliability and power.
Typical consumption is 15–18 L/100km (16–19 mpg UK) in mixed driving. Highway cruising at 120 km/h yields ~12 L/100km. Economy worsens significantly with aggressive driving due to the high displacement and enrichment under load.
Yes. The DOHC V8 is an interference design. If the timing chains jump or fail, valves can contact pistons, causing catastrophic damage. Regular inspection of chain tensioners and guides is essential to prevent failure.
Porsche specifies 10W-60 semi-synthetic oil meeting Porsche A40 specification for all M28.46 variants. Never use 15W-50 or modern low-viscosity oils. Change every 7,500–10,000 km or 6 months—whichever comes first.
Comprehensive technical documentation and regulatory references
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