The Porsche M48.51 is a 2,687 cc, water-cooled flat‑six petrol engine produced between 2005 and 2008. It features a horizontally opposed (boxer) layout, dual overhead camshafts (DOHC), and Bosch Motronic ME7.8 digital fuel injection. Output was rated at 177 kW (240 PS) @ 6,400 rpm and 290 Nm of torque, engineered for linear power delivery and high-RPM refinement in entry-level sports applications.
Fitted exclusively to the Porsche Cayman S (987) and Boxster S (987) models, the M48.51 was developed as a higher-displacement evolution of the M97/21, offering enhanced mid-range elasticity without sacrificing the characteristic flat-six balance. Emissions compliance was achieved through exhaust gas recirculation (EGR), a three-way catalytic converter, and closed-loop lambda control, meeting EU Directive 94/12/EC (Euro 4) standards.
One documented concern is premature wear of the intermediate shaft (IMS) bearing, which can lead to catastrophic engine failure if undetected. This issue, referenced in Porsche Technical Service Bulletin 987/TSB/06-03, stems from the single-row ball-bearing design used in early M48.51 units. From mid-2006, Porsche transitioned to a strengthened dual-row bearing, significantly improving longevity.
Production years 2005–2008 meet EU Directive 94/12/EC (Euro 4) standards depending on market (VCA Type Approval #VCA/EMS/7812).
The Porsche M48.51 is a 2,687 cc flat-six DOHC petrol engine engineered for mid-engine sports cars (2005–2008). It combines Bosch Motronic ME7.8 digital injection with a gear-driven valvetrain to deliver smooth high-RPM power and balanced chassis dynamics. Designed to meet Euro 4 emissions thresholds, it balances performance with regulatory compliance in the 987 platform.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,687 cc | |
| Fuel type | Petrol (RON 95 minimum, RON 98 recommended) | |
| Configuration | Flat‑6, DOHC, 24‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 89.0 mm × 72.0 mm | |
| Power output | 177 kW (240 PS) @ 6,400 rpm | |
| Torque | 290 Nm @ 4,500 rpm | |
| Fuel system | Bosch Motronic ME7.8 digital electronic injection | |
| Emissions standard | EU Directive 94/12/EC (Euro 4) | |
| Compression ratio | 10.5:1 | |
| Cooling system | Water-cooled | |
| Turbocharger | None | |
| Timing system | Gear-driven intermediate shafts (no timing belt/chain) | |
| Oil type | SAE 10W-60 synthetic (Porsche A40 spec) | |
| Dry weight | 172 kg |
The flat-six architecture provides exceptional balance and throttle linearity but requires strict adherence to 15,000 km oil changes using Porsche A40–spec 10W-60 oil to protect the intermediate shaft (IMS) bearing and cam journals. Pre-06/2006 M48.51 engines use a single-row IMS bearing prone to fatigue under thermal stress; units built after this date feature a dual-row design per TSB 987/TSB/06-03. Use only RON 95+ unleaded fuel—ethanol blends above E10 may degrade seals over time. The absence of a timing belt eliminates replacement concerns, but IMS health remains critical.
Oil Specs: Requires Porsche A40–compliant 10W-60 synthetic oil (Porsche Lubricants Bulletin LB-05-12). High-temperature stability is essential for IMS protection.
Emissions: Meets Euro 4 (EU Directive 94/12/EC) across all production years (VCA Type Approval #VCA/EMS/7812).
Power Ratings: Measured under DIN 70020 standards. Output assumes RON 98 fuel and functional emissions loop (Porsche TIS Doc. M48-TB-2007).
Porsche Technical Information System (TIS): Docs M48-TB-2005, FI-05-19, M48-TB-2007
Porsche Technical Service Bulletin 987/TSB/06-03
VCA Type Approval Database (VCA/EMS/7812)
EU Directive 94/12/EC
The Porsche M48.51 was used in the Porsche 987 platform with mid-engine, longitudinal mounting and no external licensing. This engine powered the Cayman S and Boxster S from 2005 to 2008, featuring revised displacement over the M97/21 and updated oiling for the IMS bearing. From 2009, the 987.2 facelift adopted the direct-injection MA1.01 engine. All adaptations are documented in OEM technical bulletins.
Engine type ‘M48.51’ is cast into the right-side crankcase below the exhaust manifold (Porsche WIS 135.12). The presence of a black composite intake manifold and Bosch ME7.8 ECU (Part No. 0 261 208 503) under the passenger footwell confirms identity. VIN 7th digit ‘5’ denotes Cayman S; ‘4’ denotes Boxster S. Critical differentiation from M97: M48.51 has 2,687 cc displacement (vs. 3.2–3.8L in M97) and unique oil pan shape. Service parts for IMS and valvetrain are not interchangeable with M96/M97 engines (Porsche TSB 987/TSB/07-01).
The M48.51's primary reliability risk is intermediate shaft (IMS) bearing failure, with elevated incidence in pre-mid-2006 units used in high-temperature climates or aggressive driving. Porsche internal quality data (2008) indicated IMS-related repairs in over 7% of early-build engines before 100,000 km, while DVSA MOT records cite frequent oil leaks and catalytic converter faults in UK examples due to degraded seals and thermal cycling. Extended high-RPM use without adequate oil changes accelerates IMS and cam wear.
Analysis derived from Porsche technical bulletins (2005–2008) and UK DVSA historic MOT failure statistics (2010–2022). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about PORSCHE M-48-51.
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