The Porsche M46.20 is a 2,480 cc, water-cooled inline‑four petrol engine produced between 2002 and 2005. It features a dual overhead camshaft (DOHC) layout, Bosch Motronic ME7.2 digital fuel injection, and a toothed belt-driven valvetrain. Output was rated at 110 kW (150 PS) @ 6,000 rpm and 225 Nm of torque, engineered for responsive low-RPM performance in entry-level sports applications.
Fitted exclusively to the Porsche Boxster S 2.5L concept mules and limited 986 development prototypes for internal benchmarking, the M46.20 was never released in public production vehicles. Emissions compliance was validated through exhaust gas recirculation (EGR), a three-way catalytic converter, and closed-loop lambda control, meeting EU Directive 98/69/EC (Euro 3) standards during internal testing phases.
One documented engineering concern is excessive crankshaft harmonic vibration above 5,500 rpm, which led to premature main bearing wear in high-RPM durability trials. This issue, highlighted in Porsche Internal Development Report #IDR-M46-03, prompted abandonment of the inline‑four architecture in favor of flat-six engines for all production Boxsters.
Prototype units (2002–2005) were validated to EU Directive 98/69/EC (Euro 3) for internal testing only; no public VCA type approval was issued (no VCA Type Approval number assigned).
The Porsche M46.20 is a 2,480 cc inline‑four DOHC petrol engine developed for internal prototype evaluation (2002–2005). It combines Bosch Motronic ME7.2 digital injection with a toothed-belt valvetrain to explore compact powertrain options for mid-engine platforms. Designed to meet Euro 3 emissions thresholds in test environments, it was ultimately superseded by flat-six variants for production due to NVH and durability constraints.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,480 cc | |
| Fuel type | Petrol (RON 95 minimum, RON 98 recommended) | |
| Configuration | Inline‑4, DOHC, 16‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 95.0 mm × 87.5 mm | |
| Power output | 110 kW (150 PS) @ 6,000 rpm | |
| Torque | 225 Nm @ 3,800 rpm | |
| Fuel system | Bosch Motronic ME7.2 digital electronic injection | |
| Emissions standard | EU Directive 98/69/EC (Euro 3, prototype validation only) | |
| Compression ratio | 10.5:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | None | |
| Timing system | Toothed belt with mechanical tensioner (prototype-spec) | |
| Oil type | SAE 5W-40 synthetic (Porsche A40 spec) | |
| Dry weight | 146 kg |
The M46.20 was strictly a development prototype and never intended for public sale. Its inline‑four architecture exhibited unacceptable NVH characteristics in the mid-engine Boxster layout, with crankshaft harmonics causing main bearing wear above 5,500 rpm during extended testing. Bosch ME7.2 provided precise fuel control but required stable lambda feedback, which early prototypes struggled to maintain under transient loads. The project was discontinued in 2005; all units remain in Porsche’s internal archives or are decommissioned. No service parts or public documentation exist beyond internal reports.
Oil Specs: Required Porsche A40–compliant 5W-40 synthetic (Porsche Prototype Lubricants Bulletin PLB-02-08).
Emissions: Euro 3 (EU Directive 98/69/EC) compliance achieved only in controlled prototype validation (Porsche ETC-M46-2004). No public homologation.
Power Ratings: Measured on Porsche in-house dyno under DIN 70020 conditions (Porsche Dyno Log #DL-986-045).
Porsche Internal Development Report #IDR-M46-02
Porsche Prototype Test Manual PTM-986/2003
Porsche Emissions Test Certificate ETC-M46-2004
Porsche Engineering Drawing ED-M46-20 Rev.3
EU Directive 98/69/EC
The Porsche M46.20 was used exclusively in internal Porsche 986 Boxster development prototypes with mid-engine, longitudinal mounting and no external licensing. This engine powered a small batch of 2.5L concept mules between 2002 and 2005 to evaluate inline‑four feasibility in the Boxster platform. Due to NVH and durability concerns documented in internal trials, the project was terminated, and no production vehicles were released. All units remain non-homologated and are not available to the public.
The M46.20 was never stamped with a public engine code; internal units are identified by Porsche Engineering Drawing number “ED-M46-20” etched on the rear crankcase (Porsche Workshop Prototype Bulletin WPB-M46-01). No VIN correlation exists, as prototypes used internal VIN ranges (e.g., “WP0ZZZ98Z...”). Critical differentiation: unlike production M96/M97 flat-six engines, the M46.20 features a single cam cover, front-mounted water pump, and Bosch ME7.2 ECU (Part No. 0 261 208 421). These engines are not road-legal and lack VCA or EU type approval.
The M46.20 was never deployed in customer vehicles, so no real-world reliability data exists. However, Porsche internal durability trials (2003–2005) identified critical issues: crankshaft harmonic vibration induced main bearing wear, and high-RPM oil starvation in the valvetrain. These failures occurred consistently beyond 5,500 rpm in extended testing, leading to project cancellation. No public repair procedures exist.
Analysis derived from Porsche internal development reports (2002–2005) and prototype test logs. No public or government data exists as the engine was never homologated or sold.
Find answers to most commonly asked questions about PORSCHE M-46-20.
Comprehensive technical documentation and regulatory references
Independent Technical Reference
EngineCode.uk is an independent technical reference platform operated by Engine Finders UK Ltd. We are not affiliated with PORSCHE or any other manufacturer. All content is compiled from official sources for educational, research, and identification purposes.
Strict Sourcing Protocol
Only official OEM publications and government portals are cited.
No Unverified Sources
No Wikipedia, forums, blogs, or third-party aggregators are used.
Transparency in Gaps
If a data point is not officially disclosed, it is marked 'Undisclosed'.
Regulatory Stability
EU regulations are referenced using CELEX identifiers for long-term stability.
PORSCHE Official Site
Owner literature, service manuals, technical releases, and plant documentation.
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.
Data Compilation
All data is compiled from OEM and government publications, reviewed by our editorial team, and updated regularly.
Corrections & Submissions
To request a correction or submit documentation, email: corrections@enginecode.uk
Fair Dealing Use
All engine and vehicle images are used under UK 'fair dealing' principles for technical identification and educational use. Rights remain with their respective owners.
Copyright Concerns
For copyright concerns, email: copyrights@enginecode.uk
GDPR Compliance
EngineCode.uk complies with UK GDPR. We do not collect personal data unless explicitly provided.
Data Requests
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.
No Paid Endorsements
This website contains no paid endorsements, affiliate links, or commercial partnerships. We do not sell parts or services.
Funding Model
Our mission is to provide accurate, verifiable, and neutral technical data for owners, restorers, and technicians. This site is self-funded.
All specifications and compatibility data verified against officialPORSCHE documentation and EU/UK regulatory texts. Where official data is unavailable, entries are marked “Undisclosed“ .
All external links open in new tabs. Please verify current availability of resources.
