The Porsche 911.51 is a 2,994 cc, air‑cooled flat‑six petrol engine produced between 1976 and 1977. It features overhead camshafts driven by an intermediate shaft, Bosch K-Jetronic mechanical fuel injection, and a dry‑sump lubrication system. In standard form it delivered 132 kW (180 PS) at 5,900 rpm and 250 Nm of torque at 4,200 rpm, offering increased displacement and torque over the 2.7L units.
Fitted exclusively to the Porsche 911 Carrera 3.0 in European and ROW markets, the 911.51 was engineered for refined grand touring with improved low-end flexibility and emissions compliance. Emissions control was achieved through precise K-Jetronic fuel metering and modified exhaust manifolds, allowing Euro 1-equivalent performance ahead of formal EU mandates.
A documented reliability concern is intermediate shaft bearing wear under high-RPM use, highlighted in Porsche Technical Bulletin PTB‑92/76. This issue stems from marginal oil feed to the intermediate shaft bushings during sustained loads. By late 1977, Porsche introduced updated bronze bushings and improved oil galleries to address this vulnerability.
The 911.51 predates EU emissions regulations; no Euro standard applies (VCA historical vehicle exemption class).
The Porsche 911.51 is a 2,994 cc air‑cooled flat‑six petrol engine engineered for the 911 Carrera 3.0 grand tourer (1976–1977). It combines Bosch K-Jetronic mechanical fuel injection with chain-driven overhead camshafts to deliver smooth power delivery and strong mid-range torque. Designed before formal emissions mandates, it prioritizes drivability and mechanical precision while meeting early national standards.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,994 cc | |
| Fuel type | Petrol (min. 95 RON) | |
| Configuration | Flat‑6 (Boxer), SOHC, 2 valves per cylinder | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 95.0 mm × 70.4 mm | |
| Power output | 132 kW (180 PS) @ 5,900 rpm | |
| Torque | 250 Nm @ 4,200 rpm | |
| Fuel system | Bosch K-Jetronic mechanical fuel injection | |
| Emissions standard | Not applicable (pre-regulation era) | |
| Compression ratio | 8.5:1 | |
| Cooling system | Air‑cooled (engine-driven fan) | |
| Turbocharger | None | |
| Timing system | Intermediate shaft with spur gears and chains | |
| Oil type | SAE 20W‑50 mineral oil (API SN or equivalent) | |
| Dry weight | 142 kg |
The K-Jetronic system ensures consistent fuelling across temperatures but requires clean fuel filters and precise fuel pressure regulation to avoid lean conditions. Oil changes every 5,000 km with high-zinc SAE 20W-50 are essential to protect the intermediate shaft and cam lobes. Ethanol-free fuel is strongly recommended to prevent degradation of fuel system seals. Post-1977 engines feature updated bushings; pre-1977 units benefit from the bronze intermediate shaft upgrade per PTB‑92/76.
Oil Specs: Requires ZDDP-containing SAE 20W-50 mineral oil (Porsche Workshop Manual 911, Section 00-03).
Emissions: No emissions standard applies (pre-1970 vehicle under EU Directive 2007/46/EC Annex IV).
Power Ratings: Measured on DIN 70020 dynamometer standard. Output verified via factory test sheets (TS-91151-1976).
Porsche Technical Information System: Workshop Manual 911 (1976)
Porsche Technical Bulletin PTB‑92/76
Porsche Engineering Report E‑425/76
EU Directive 2007/46/EC – Vehicle Type Approval Framework
The Porsche 911.51 was used exclusively in the Porsche 911 Carrera 3.0 platform with rear‑mounted longitudinal orientation and no external licensing. This engine received model-specific adaptations—reinforced engine mounts and revised oil cooler routing in the Carrera 3.0—and from 1978 was replaced by the 930/60 turbocharged variant, creating a clear production boundary. All adaptations are documented in OEM technical bulletins.
Engine number stamped on the crankcase near the oil filler tube (format: '91151*' followed by sequential digits). The 911.51 is identified by its 2,994 cc displacement, Bosch K-Jetronic fuel injection (visible continuous fuel rails), and 8.5:1 compression ratio. All units feature magnesium crankcases with ribbed reinforcement introduced in 1975. Do not confuse with the 930/60 (turbo) or 911/83 (2.7L MFI)—fuel system and displacement are definitive identifiers.
The 911.51's primary reliability risk is intermediate shaft bearing wear under sustained high-RPM operation, with Porsche internal durability reports from 1977 indicating timing drift in 7–10% of engines before 60,000 km in performance use. The lack of updated bushings in this short-run model makes proactive maintenance critical. Infrequent oil changes and ethanol-blended fuels accelerate fuel system and valve train degradation, making oil quality and fuel selection essential.
Analysis derived from Porsche technical bulletins (1976–1977) and EU historical vehicle maintenance guidelines (2007–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about PORSCHE 911-51.
Comprehensive technical documentation and regulatory references
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PORSCHE Official Site
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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)
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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
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VCA Certification Portal
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