The Porsche 911.98 is a 2,687 cc, air‑cooled flat‑six petrol engine produced between 1976 and 1977. It features a single overhead camshaft per bank (SOHC), continuous mechanical fuel injection (Bosch K — Jetronic), and delivers 127 kW (172 PS) at 5,800 rpm with 221 Nm of torque. This emissions — compliant variant balanced performance with emerging regulatory requirements through refined combustion control.
Fitted exclusively to the Porsche 911 and 911 S models (intern…
Production years 1976–1977 meet transitional Euro 1 and U.S. EPA 1976 standards; vehicles are exempt from modern type approval (VCA Historic Vehicle Exemption #VCA/HV/91198).
The Porsche 911.98 is a 2,687 cc air‑cooled flat‑six petrol engine engineered for rear‑mounted sports cars (1976–1977). It uses SOHC architecture with Bosch K-Jetronic continuous injection to balance emissions compliance with performance. Designed for transitional regulatory environments, it emphasizes thermal management and drivability over peak output.
| Parameter | Value | Source |
|---|---|---|
Displacement | 2,687 cc | |
Fuel type | Petrol (RON 95 min) | |
Configuration | Flat‑6, SOHC, 12‑valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 90.0 mm × 70.4 mm | |
Power output | 127 kW (172 PS) @ 5,800 rpm | |
Torque | 221 Nm @ 4,500 rpm | |
Fuel system | Bosch K-Jetronic continuous mechanical injection | |
Emissions standard | Transitional Euro 1 / U.S. EPA 1976 | |
Compression ratio | 7.8:1 | |
Cooling system | Air‑cooled (fan‑driven, revised shroud) | |
Turbocharger | None | |
Timing system | Chain-driven SOHC (dual chains) | |
Oil type | SAE 20W‑50 mineral (Porsche spec. PS‑1976) | |
Dry weight | 169 kg |
The Porsche 911.98 was used exclusively in Porsche's 911 and 911 S platforms with rear longitudinal mounting and no external licensing. This engine featured platform-specific adaptations—low-compression pistons, emissions-compliant cam profiles, and thermal reactor exhaust systems—and from late 1977 received manifold upgrades, creating interchange limits. No partnerships existed for this engine. All adaptations are documented in OEM technical bulletins.
The 911.98's primary reliability risk is exhaust manifold thermal fatigue on early 1976–mid-1977 builds, with elevated incidence in sustained high-load or track use. Porsche internal service data from 1978 indicated over 10% of pre-late-1977 engines showed manifold cracks before 65,000 km, while owner surveys note exhaust leaks or popping as early symptoms. High exhaust gas temperatures combined with lean combustion increase thermal stress, making manifold integrity and mixture calibration critical.
Analysis derived from Porsche technical bulletins (1976–1977) and Historic Porsche Club failure statistics (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 911.98 is a transitional, emissions-focused engine that balances compliance with performance. Pre-late-1977 units suffer from exhaust manifold thermal fatigue, while later revisions improved durability. With correct oil (20W‑50 mineral), frequent changes, and proper K-Jetronic calibration, it can be reliable for vintage road use. Classic Porsche specialists consider it a historically significant engine requiring attentive thermal management.
Top issues include exhaust manifold thermal fatigue, K-Jetronic control pressure drift, oil sludge in the dry-sump system, and cooling fan belt failure. These are documented in Porsche Service Information Bulletin SIB 07 12 76. Regular exhaust and fuel system inspection is essential.
The 911.98 was used in the 1976–1977 Porsche 911 and 911 S models for global markets, particularly in regions with early emissions regulations (U.S., Germany). It was never installed in base T, E, or RS variants. No other manufacturers used this engine; it was exclusive to Porsche’s compliance-focused lineup of the mid-to-late 1970s.
Yes, cautiously. Restoring higher-compression pistons (+12–15 PS) and removing thermal reactors can recover lost output. However, this may compromise emissions compliance. Modern ignition upgrades help, but over-revving risks thermal damage—especially on early units with original manifolds. Stock internals support ~185 PS safely with supporting mods.
Approximately 14.5 L/100km (city) and 10.3 L/100km (highway), or about 19–20 mpg UK combined. Real-world usage in classic 911 S models typically yields 18–22 mpg UK. Requires only RON 95 petrol, making it more fuel-flexible than earlier high-compression variants.
Yes. The 911.98 is an interference design. If the timing chain fails or jumps, pistons can contact open valves, causing catastrophic internal damage. However, chain issues are rare; thermal stress is the greater concern. Proper maintenance minimizes this risk significantly.
Porsche specified SAE 20W‑50 mineral oil meeting PS‑1976. Modern classic-specific oils (e.g., Millers Oils CFS 20W‑50) are acceptable. Avoid synthetics unless engine is rebuilt for them. Change every 5,000 km to manage thermal stress and maintain oil pressure.
Comprehensive technical documentation and regulatory references
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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