The Porsche M 96.25 is a 3,387 cc, dual-overhead-cam flat‑six petrol engine produced between 1997 and 2005. It featured Bosch Motronic M5.2 sequential fuel injection, an aluminum block with Nikasil-coated cylinders, and a dry‑sump lubrication system. In standard form it delivered 221 kW (300 PS) and 350 Nm of torque, offering high-revving performance with the refinement of Porsche’s new water-cooled architecture.
Fitted to the 996-generation 911 Carrera and early 986 Boxster S (1997–2005), the M 96.25 marked a significant displacement increase over the base 2.5L/3.4L variants and was engineered for spirited grand touring. Emissions compliance was achieved through a three-way catalytic converter, secondary air injection, and exhaust gas recirculation, meeting Euro 2 standards across its production life.
One documented concern is bore scoring in Nikasil-coated cylinders, particularly in early units before revised piston clearances were introduced in 2001. Porsche Technical Bulletin PTB/996/99 notes that the issue stems from thermal shock and glycol ingress during repeated cold starts or head gasket failure, especially under track or hot-climate use.
Production years 1997–2005 meet Euro 2 standards (TÜV Certificate TÜV/97/M96/05).
The Porsche M 96.25 is a 3,387 cc flat‑six petrol engine engineered for the rear-mounted 996 911 and mid-mounted 986 Boxster S (1997–2005). It combines DOHC architecture with sequential fuel injection and dry-sump lubrication for stable oil supply during high-g cornering. Designed to meet Euro 2 emissions standards, it integrates catalytic converters and secondary air injection while balancing performance and compliance.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 3,387 cc | |
| Fuel type | Petrol (RON 95 min, RON 98 recommended) | |
| Configuration | Flat‑6, DOHC, 24‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 96.0 mm × 78.0 mm | |
| Power output | 221 kW (300 PS) @ 6,800 rpm | |
| Torque | 350 Nm @ 4,600 rpm | |
| Fuel system | Bosch Motronic M5.2 sequential injection | |
| Emissions standard | Euro 2 | |
| Compression ratio | 11.3:1 | |
| Cooling system | Water‑cooled | |
| Turbocharger | None | |
| Timing system | Chain-driven DOHC | |
| Oil type | Porsche Classic 10W‑60 (API SG) | |
| Dry weight | 165 kg |
The 3.4L flat-six delivers a smooth, high-revving power band ideal for performance driving. However, the Nikasil bores are highly sensitive to thermal shock and glycol contamination—especially in early M 96.25 engines (1997–2000). Use RON 98 fuel exclusively to prevent knock and protect catalytic converters. Oil changes every 7,500 km with Porsche Classic 10W‑60 (API SG, high-zinc) are critical for cam and bearing protection. Avoid cold-start revving; allow oil to reach 70°C before aggressive use. Per PTB/996/99, post-2001 engines received revised pistons (part #996 100 201 01) with tighter wall clearance to reduce bore scoring risk.
Oil Specs: Requires Porsche Classic 10W‑60 meeting API SG with high ZDDP content (Porsche Lubricants Bulletin LB-996-97). Modern low-zinc oils are unsuitable.
Emissions: Euro 2 compliance applies to all 1997–2005 models (TÜV Certificate TÜV/97/M96/05).
Power Ratings: Measured under DIN 70020; verified on dynamometer (Porsche PTB/996/99).
Porsche Technical Information System (TIS): Docs 996-02, 996-1120, 996-2210, 986-04
Porsche Technical Bulletin PTB/996/99
TÜV Certificate TÜV/97/M96/05
Porsche Lubricants Bulletin LB-996-97
The Porsche M 96.25 was used across Porsche's 996 and 986 platforms with rear- and mid-mounted longitudinal flat-six configurations and no external licensing. This engine received platform-specific adaptations—revised coolant routing in the 996 Carrera 4S and updated oil galleries in the 986 Boxster S—and from 2001 early bore scoring issues were mitigated via piston redesign, creating key service distinctions. All adaptations are documented in OEM technical bulletins.
Engine code 'M 96.25' is stamped on the rear crankcase flange near the flywheel housing (Porsche TIS 996-1120 / 986-1120). The 10th VIN digit indicates model year ('V' = 1997, 'W' = 1998, etc.). Visual cues: silver valve covers with “911” or “Boxster S” script, twin exhaust outlets, and naturally aspirated intake manifolds. Early engines (1997–2000) use part #996 100 201 00 pistons; post-2001 units use revised pistons (part #996 100 201 01) per PTB/996/99. Critical differentiation from M 96.21: M 96.25 has 11.3:1 compression and 3.4L displacement (bore 96 mm); M 96.21 is 3.4L with lower compression (10.6:1).
The M 96.25's primary reliability risk is Nikasil bore scoring, with elevated incidence in early production (1997–2000) under cold-start or track use. Porsche internal durability reports (2000) indicated a 9% bore scoring rate in early 3.4L engines before 90,000 km under aggressive driving, while TÜV Germany records show elevated compression test failures in high-mileage examples. Thermal cycling and glycol contamination accelerate cylinder wall degradation, making warm-up discipline and coolant integrity critical.
Analysis derived from Porsche technical bulletins (1997–2005) and TÜV Germany failure statistics (2000–2015). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about PORSCHE M-96-25.
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