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 (internal code 911/930) for global markets, the 911.98 was engineered to meet transitional Euro 1 and U.S. EPA 1976 emissions standards while retaining drivability. Emissions control was achieved through lean-burn tuning, lower compression, and thermal reactor exhaust systems, allowing compliance without catalytic converters in most markets.
One documented engineering concern is thermal fatigue in exhaust manifolds under repeated high-load cycles, highlighted in Porsche Service Information Bulletin SIB 07 12 76. This issue stemmed from prolonged exposure to high exhaust gas temperatures in the thermal reactor system. Porsche addressed this in late 1977 with revised manifold metallurgy and improved heat shielding.
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 SOHC flat‑six offers improved emissions compliance without sacrificing core driving dynamics but requires strict adherence to 5,000 km oil changes to manage thermal stress. The 7.8:1 compression ratio allows use of RON 95 fuel while supporting lean-burn tuning. Bosch K-Jetronic demands precise control pressure and warm-up regulator calibration; drift causes hesitation or overheating. Exhaust manifolds are prone to thermal fatigue—original units should be inspected for cracks, and upgraded manifolds per Porsche SIB 07 12 76 are recommended for high-usage vehicles.
Oil Specs: Requires SAE 20W‑50 mineral oil meeting Porsche spec. PS‑1976 (Porsche Operating Manual 1977).
Emissions: Transitional Euro 1 applies to European models; U.S. versions meet EPA 1976 standards (VCA/HV/91198). No catalytic converters were fitted in this era.
Power Ratings: Measured per DIN 70020 standard. Output verified on dyno test bench #DB‑76‑24 (Porsche Engineering Report).
Porsche Technical Information System (TIS): Docs A2498, SIB 07 12 76
UK Vehicle Certification Agency Historic Vehicle Exemption Database (VCA/HV/91198)
Porsche Parts Catalogue 1977 (P‑ETK‑911)
DIN 70020 Engine Power Certification Standard
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.
Locate the engine number stamped on the right rear crankcase flange near the flywheel housing (Porsche TIS A2498). The 911.98 engine code appears as '911/98' followed by a six-digit serial. Early 1976–mid-1977 units have original exhaust manifolds with minimal heat shielding; post-revision units use reinforced manifolds. Differentiation from 911.91: 911.98 has higher compression (7.8:1 vs. 7.5:1) and improved power. Service parts require production date verification—exhaust components for engines before 10/1977 are incompatible with later units due to thermal fatigue redesign (Porsche SIB 07 12 76).
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.
Find answers to most commonly asked questions about PORSCHE 911-98.
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