The Porsche M 28.21 is a 2,993 cc, water — cooled inline‑six petrol engine produced between 1982 and 1986. It features a single overhead camshaft (SOHC), Bosch L — Jetronic electronic fuel injection, and a crossflow cylinder head. In standard form it delivered 132 kW (180 PS) and 255 Nm of torque, offering smooth power delivery suited to grand touring.
Fitted exclusively to the first — generation Porsche 928 (G — model), the M 28.21 was engineered to provide refined, linear pe…
Production years 1982–1986 meet Euro 1-equivalent standards in EU markets . US models comply with EPA Tier 0.
The Porsche M 28.21 is a 2,993 cc inline‑six SOHC petrol engine engineered for the 928 grand tourer (1982–1986). It combines Bosch L-Jetronic electronic fuel injection with a single camshaft and crossflow head to deliver smooth, linear power ideal for long-distance driving. Designed to meet early catalytic converter emissions standards, it balances refinement with period-appropriate efficiency.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,993 cc | |
Fuel type | Petrol | |
Configuration | Inline‑6, SOHC, 12‑valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 84.0 mm × 90.0 mm | |
Power output | 132 kW (180 PS) @ 5,250 rpm | |
Torque | 255 Nm @ 3,500 rpm | |
Fuel system | Bosch L-Jetronic electronic injection | |
Emissions standard | Euro 1-equivalent (EU); EPA Tier 0 (US) | |
Compression ratio | 9.3:1 | |
Cooling system | Water-cooled with dual-circuit radiator | |
Turbocharger | None | |
Timing system | Chain-driven SOHC (single-stage) | |
Oil type | 15W‑50 mineral or semi-synthetic (Porsche A40 spec) | |
Dry weight | 198 kg |
The Porsche M 28.21 was used exclusively in Porsche's 928 platform with front-engine, longitudinal mounting and no external licensing. This engine received platform-specific adaptations—front-mounted alternator and unique exhaust manifolds—and from 1985 the 928 S2 transitioned to the M 28/40, creating clear interchange limits. All adaptations are documented in OEM technical bulletins.
Engine Finders UK Ltd, which operates EngineCode.uk, can pass your enquiry to engine suppliers in the UK. The service is for vehicles in the United Kingdom, with UK delivery or fitting. This is a commercially connected service, and sending an enquiry does not confirm diagnosis or compatibility.
Diagnostic reminder: If a technician has recommended replacing the engine, you can send an enquiry to engine suppliers in the UK. Confirm the diagnosis first: an engine-code record does not diagnose a fault.
Field reports and technical service bulletins highlight component wear patterns under high-load operation. Adherence to manufacturer service intervals and approved fluid specifications is critical for long-term reliability.
Analysis derived from manufacturer technical service bulletins and industry workshop records. Repair procedures should follow manufacturer guidelines.
The most common questions about engine codes, what they mean, how to find them and how this database works
The M 28.21 is fundamentally robust but requires diligent maintenance due to its age. Key concerns are vacuum leaks, grounding issues, and coolant pipe degradation. With proper care—regular oil changes, ground inspections, and use of quality fuel—it can remain dependable even beyond 200,000 km.
Top issues include cracked vacuum ports on the intake manifold, L-Jetronic ECU grounding faults, timing chain tensioner wear, and coolant crossover pipe leaks. These are documented in Porsche TSB‑928‑84‑12 and TIS repair guides. Most are preventable with proactive inspection.
The M 28.21 was used only in the Porsche 928 from 1982 to 1986, powering base and early S variants. It was replaced by the 3.3L M 28/40 in the 928 S2 from 1986 onward. No other Porsche or external manufacturer used this engine.
Modest gains are possible: upgrading to 3.3L components (head, crank) or converting to D-Jetronic/Motronic yields 200+ PS. However, the SOHC design limits high-RPM potential. Most owners prioritize reliability over tuning due to the engine’s classic status.
Expect ~12–14 L/100km (19–23 mpg UK) in mixed driving. Highway cruising yields ~10 L/100km (28 mpg UK). Consumption is higher than modern engines due to low compression and older injection efficiency, but reasonable for a 3.0L V8-era GT.
No. The M 28.21 is a non-interference engine. If the timing chain fails, pistons will not contact valves. However, incorrect timing can still cause poor running or backfires, so periodic tensioner inspection is advised.
Porsche specifies 15W‑50 mineral or semi-synthetic oil meeting Porsche A40 standards. Modern low-viscosity oils are not recommended due to compatibility with older cam and bearing materials. Change every 7,500 km or annually.
Comprehensive technical documentation and regulatory references
EngineCode.uk is operated by Engine Finders UK Ltd. It provides engine-reference information and an optional commercial enquiry service. It is not an official manufacturer website. Check the record's sources and confirm vehicle-specific details before relying on it for parts, repairs or replacement.
Our editorial standard prioritises relevant manufacturer documentation and official regulatory sources. The sources and verification status for a record should be checked alongside the data.
A statement is not verified merely because a source is listed. Where supporting evidence is missing or conflicting, the record should identify that limitation. Please report unsupported or inconsistent information.
Transparency in gaps
A missing or unverified value does not mean the manufacturer has withheld it. We distinguish information not yet verified, information not available to us, and information explicitly not disclosed by the source.
Regulatory Stability
EU regulations are referenced using CELEX identifiers for long-term stability.
EUR-Lex
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.
Records are subject to review and correction. Source links, dates and verification notes should be read with the technical information. Our Editorial and Sourcing Policy explains our standards and review process.
Found an error or missing source? Report a problem with this page. Include the field or statement concerned and a supporting source if available. You can also email corrections@enginecode.uk.
Copyright and permissions
Images and other material may be protected by copyright. Attribution does not by itself grant permission to reuse material. If you believe material on this site infringes your rights, contact copyrights@enginecode.uk with the page URL and details of your claim. We will review the material and take appropriate action.
Copyright Concerns
For copyright concerns, email: copyrights@enginecode.uk
Our Privacy Policy explains how Engine Finders UK Ltd uses information from visits, vehicle lookups, enquiries and messages. Our Cookie Policy explains cookies and similar technologies and how to change your choices.
For access, correction, or deletion requests, email: gdpr@enginecode.uk
Trademark Notice
All trademarks, logos, and engine codes are the property of their respective owners. Use on this site is strictly for reference and identification.
Ownership and commercial services
EngineCode.uk is owned and operated by Engine Finders UK Ltd. Alongside our reference content, we offer an optional replacement-engine enquiry service through Engine Finders and may identify relevant services provided by businesses connected with us. These commercial connections are disclosed. Using an enquiry service is not required to read our reference content.
Engine Finders UK Ltd operates this website. Our optional enquiry service has a commercial purpose. Our Ownership and Commercial Disclosure explains the relationship between the reference website and that service. Participating suppliers pay a fee or subscription to participate on the network and receive quote requests.
Use this record as a starting point for identification. Specifications and vehicle applications may contain errors or omissions. Confirm the exact engine variant and compatibility using vehicle-specific documentation and a qualified supplier or technician.
All external links open in new tabs. Please verify current availability of resources.