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, and GTS variants, the M28.46 was engineered for refined high-speed performance with emphasis on throttle response, exhaust note, and thermal stability. Emissions compliance in European markets was achieved through three-way catalytic converters and oxygen sensor feedback, allowing adherence to Euro 1 standards from launch.
One documented concern is cylinder head bolt thread stripping in the aluminum block, highlighted in Porsche Technical Bulletin PTB/89/11. This issue stems from thermal cycling and the high clamping loads required for the large displacement V8’s head gaskets. In 1992, Porsche introduced case revisions with reinforced thread inserts and updated torque-to-yield fasteners to mitigate head gasket failure under extended high-load operation.
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 DOHC V8 delivers smooth, high-torque performance ideal for continent-crossing grand touring, but demands strict adherence to head bolt torque procedures and oil specifications to prevent head gasket failure. Use of 10W-60 semi-synthetic oil meeting Porsche A40 spec is mandatory for high-temperature film strength. Cold starts below 0°C require 10+ minutes of gentle warm-up before high-load use. The LH-Jetronic system requires OEM-spec oxygen sensors and fuel pressure regulators—non-compliant parts cause mixture instability and catalytic converter damage. Post-1992 engines feature reinforced block threads; pre-1992 units should receive the updated head bolt kit per Porsche bulletin PTB/89/11 during head gasket service.
Oil Specs: Requires 10W-60 semi-synthetic oil meeting Porsche A40 specification (Porsche Tech Bulletin PTB/89/11). ACEA A3/B3 oils are not sufficient for thermal stability.
Emissions: All M28.46 variants meet Euro 1 standards across all production years (1986–1995) as confirmed by KBA Type Approval #KBA/928/7204.
Power Ratings: Measured under DIN 70020 standards. 350 PS GTS output requires 98 RON fuel and optimal catalytic converter function (Porsche TIS Doc. P928‑94B).
Porsche Technical Information System (TIS): Docs P928‑86A, P928‑88C, P928‑94B
KBA Type Approval Database (KBA/928/7204)
DIN 70020 Engine Power Measurement Standard
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.
Engine code is stamped on the left cylinder bank near the rear cam cover (Porsche TIS P928‑86A). The 7th–8th VIN digits are '92' for all 928 models; the engine displacement is confirmed by '28.46' in factory documentation. S4 models feature silver cam covers; GT and GTS use black cam covers with red timing marks. GTS engines have larger throttle bodies (82 mm vs. 78 mm) and high-flow injectors (324 cc/min). Pre-1992 blocks lack thread inserts in head bolt holes—visible only during disassembly—but engine serial number prefix '610.46' indicates displacement and year. Always verify against ETK for service part compatibility.
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.
Find answers to most commonly asked questions about PORSCHE M-28-46.
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