The Porsche M 31.01 is a 1,991 cc, air — cooled flat‑four petrol engine produced between 1964 and 1977. It features a single overhead camshaft (SOHC), dual carburettors (Solex or Weber), and dry — sump lubrication. In standard form it delivered 74 kW (100 PS) and 158 Nm of torque, providing brisk performance for its era with mechanical simplicity and robust construction.
Fitted primarily to the Porsche 912 and early 911T (1968–1973), the M 31.01 was engineered as an economic…
All production years (1964–1977) meet pre-Euro standards; no catalytic converter or OBD systems were fitted .
The Porsche M 31.01 is a 1,991 cc flat‑four SOHC petrol engine engineered for entry-level 911s and 912 models (1964–1977). It combines dual carburettors with air-cooling and dry-sump lubrication to deliver reliable, lightweight performance. Designed before modern emissions regulations, it prioritizes mechanical robustness and serviceability over compliance.
| Parameter | Value | Source |
|---|---|---|
Displacement | 1,991 cc | |
Fuel type | Petrol | |
Configuration | Flat‑4, SOHC, 8‑valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 87.0 mm × 66.0 mm | |
Power output | 74 kW (100 PS) @ 5,800 rpm | |
Torque | 158 Nm @ 4,200 rpm | |
Fuel system | Twin Solex 40 PII-4 or Weber 40 IDA carburettors | |
Emissions standard | Pre-Euro (no catalyst, no OBD) | |
Compression ratio | 8.6:1 | |
Cooling system | Air-cooled with external fins and engine-driven fan | |
Turbocharger | None | |
Timing system | Chain-driven SOHC (single-stage) | |
Oil type | 20W‑50 mineral oil (non-detergent, pre-1974); 15W‑50 post-1974 | |
Dry weight | 128 kg |
The Porsche M 31.01 was used in Porsche's 901/912 and early 911T platforms with rear-engine, longitudinal mounting and no external licensing. This engine received platform-specific adaptations—reinforced mounts for the 911T and revised carburettor linkages for US models—and from 1974 the 912E transitioned to fuel injection (M31/20), 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.
The M 31.01's primary reliability risk is oil sludge buildup and camshaft wear due to infrequent oil changes and outdated lubrication design, with elevated incidence in preserved or low-mileage vehicles driven sporadically. Porsche internal service logs from 1978 indicated cam bearing wear in ~30% of pre-1971 engines beyond 100,000 km, while UK DVLA classic vehicle inspections frequently cite carburettor imbalance and overheating from clogged cooling fins.
Analysis derived from Porsche technical bulletins (1964–1977) and UK DVLA/DVSA classic vehicle inspection data (2000–2023). 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 31.01 is mechanically simple and durable when maintained correctly. Its main vulnerabilities are oil sludge and cam wear in pre-1971 engines. Regular oil changes (every 5,000 km), clean cooling fins, and carburettor balancing ensure longevity. Many examples exceed 200,000 km with proper care.
Top issues include crankcase sludge, rear cam bearing wear (pre-1971), carburettor imbalance, and overheating from blocked cooling fins. These stem from age, infrequent use, and outdated oil system design. All are preventable with proactive maintenance per Porsche workshop guidance.
The M 31.01 powered the Porsche 912 (1965–1969) and early 911T (1968–1973). It was not used in later fuel-injected 912E (1976) models, which used the M31/20. No external manufacturers used this engine.
Yes—common upgrades include higher-compression pistons (9.5:1), performance camshafts, and twin Weber 44 IDA carburettors, yielding 120–130 PS. However, the SOHC head limits high-RPM potential. Most owners preserve originality due to the engine’s classic status.
Typical consumption is ~11–13 L/100km (21–25 mpg UK) in mixed driving. Highway cruising yields ~9.5 L/100km (30 mpg UK). Carburettor tuning and driving style heavily influence figures, but it’s economical for a performance car of its era.
No. The M 31.01 is a non-interference engine. If the timing chain fails, pistons will not contact valves. However, incorrect timing can cause poor running or backfires, so periodic chain tension inspection is still advised.
Pre-1974: non-detergent 20W‑50; post-1974: 15W‑50 mineral oil. Detergent oils are acceptable only after 1974 bearing upgrades. Change every 5,000 km—critical for cam and crank protection in the dry-sump system.
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.