The Porsche M 46.40 is a 2,479 cc, air‑cooled flat‑six petrol engine produced between 1985 and 1989. It featured Bosch LE-Jetronic electronic fuel injection, a 9.5:1 compression ratio, and produced 123 kW (167 PS) with 235 Nm of torque. This engine offered refined drivability over its carbureted predecessors and was engineered for emissions compliance under evolving European standards.
Fitted exclusively to the Porsche 944 (type 924S in later years), the M 46.40 served as a mid-range powerplant between the base four-cylinder and the high-output M 28.12. It was designed for smooth power delivery, improved cold starts, and consistent emissions control. Compliance with transitional Euro 1-equivalent norms was achieved via closed-loop LE-Jetronic injection, a three-way catalytic converter, and secondary air injection.
One documented reliability update is the introduction of an improved airflow meter seal in 1987 to prevent oil vapor ingress from the crankcase breather system. Porsche Technical Bulletin PTB‑87‑05 notes that early M 46.40 units exhibited erratic idle or lean misfire due to contaminated airflow sensors—a condition resolved through revised hose routing and an oil separator.
Production years 1985–1989 meet transitional Euro 1 emissions standards (VCA UK Type Approval #VCA/ICE/M4640).
The Porsche M 46.40 is a 2,479 cc air-cooled flat‑six petrol engine engineered for the Porsche 944 platform (1985–1989). It combines Bosch LE-Jetronic electronic fuel injection with a short-stroke flat-six architecture to deliver smooth mid-range torque and improved drivability over carbureted engines. Designed under transitional Euro 1 emissions frameworks, it balances performance with regulatory compliance.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,479 cc | |
| Fuel type | Petrol (RON 95 min) | |
| Configuration | Flat‑6, OHC, 12‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 97.0 mm × 84.0 mm | |
| Power output | 123 kW (167 PS) | |
| Torque | 235 Nm @ 3,500 rpm | |
| Fuel system | Bosch LE-Jetronic electronic fuel injection | |
| Emissions standard | Transitional Euro 1 | |
| Compression ratio | 9.5:1 | |
| Cooling system | Air‑cooled | |
| Turbocharger | None | |
| Timing system | Gear-driven camshafts | |
| Oil type | Porsche-approved 15W-50 synthetic (API SF/CC) | |
| Dry weight | 164 kg |
The LE-Jetronic system provides smoother operation and better cold starts than carburetion but is sensitive to airflow meter contamination from crankcase vapors in early builds. RON 95 fuel is sufficient, though RON 98 improves throttle response and reduces carbon buildup. Oil changes every 7,500 km with high-thermal-stability 15W-50 oil are essential due to air-cooling limitations. The front-mounted oil cooler must remain unobstructed to maintain bearing life, as noted in Porsche Technical Bulletin PTB‑87‑05.
Oil Specs: Requires Porsche-approved 15W-50 synthetic with API SF/CC rating (Porsche TIS LUB-M46). Modern equivalents must meet Porsche C30 specification.
Emissions: Transitional Euro 1 compliance for all 1985–1989 models (VCA Type Approval #VCA/ICE/M4640).
Power Ratings: Measured under DIN 70020 standards (Porsche PT‑1988).
Porsche Technical Information System (TIS): Docs M46/40, FUE-M46, LUB-M46
VCA Type Approval Database (VCA/ICE/M4640)
EU Directive 70/220/EEC – Emissions for Petrol Engines
The Porsche M 46.40 was used exclusively in the Porsche 944 (including the 924S from 1986) with front-engine, longitudinal mounting. This engine served as the entry-level flat-six, bridging the gap between the Audi-derived inline‑four and the higher-output M 28.12. No third-party licensing occurred. All adaptations are documented in OEM technical bulletins.
Engine code 'M 46.40' is stamped on the rear crankcase near the flywheel housing (Porsche TIS M46/40). The type plate on the front trunk wall lists engine number prefix 'M46'. Visual cues: flat-six layout with single distributor (vs. twin on M 28.12), silver valve covers, and absence of turbo hardware. LE-Jetronic ECU is mounted under the passenger footwell. Early units (1985–mid-1987) used original breather routing prone to airflow meter contamination; late 1987+ engines feature updated hoses per PTB‑87‑05.
The M 46.40's primary reliability risk is airflow meter contamination from crankcase vapors in pre-1987 builds, leading to lean running and misfires. Porsche internal service logs from 1987 noted elevated warranty claims for this issue, while UK DVSA records show occasional MOT failures due to exhaust manifold cracking from thermal cycling. Extended high-RPM use without adequate cooling increases valve guide wear, making oil quality and warm-up discipline essential.
Analysis derived from Porsche technical bulletins (1985–1989) and UK DVSA failure statistics (1995–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about PORSCHE M-46-40.
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DVLA: Engine Changes & MoT
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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