The Porsche M 28.50 is a 3,164 cc, naturally aspirated flat‑six petrol engine produced between 1986 and 1989. It features Bosch LH — Jetronic fuel injection, hydraulic valve lifters, and a horizontally opposed six‑cylinder layout with a single overhead camshaft per bank. In the 911 Carrera (G — model) it produced 184 kW (250 PS) and 285 Nm of torque, marking the final evolution of the air‑cooled SOHC 911 engine before the 3.2 Carrera update.
Fitted to the 1986–1989 911 Carrer…
Production years 1986–1989 meet Euro 1 emissions standards in EU markets (VCA UK Type Approval #VCA/EMS/2105). U.S. models comply with EPA Tier 0 regulations.
The Porsche M 28.50 is a 3,164 cc naturally aspirated flat-six petrol engine engineered for the final G-model 911 Carrera (1986–1989). It combines Bosch LH-Jetronic fuel injection with hydraulic valve lifters to deliver smooth power delivery and improved emissions compliance. Designed to meet Euro 1 standards, it represents the last iteration of the SOHC air-cooled lineage before the transition to the 3.2-liter Carrera.
| Parameter | Value | Source |
|---|---|---|
Displacement | 3,164 cc | |
Fuel type | Petrol (RON 95 min) | |
Configuration | Flat‑6, SOHC, 12‑valve | |
Aspiration | Naturally aspirated | |
Bore × stroke | 95.0 mm × 74.4 mm | |
Power output | 184 kW (250 PS) @ 5,900 rpm | |
Torque | 285 Nm @ 4,800 rpm | |
Fuel system | Bosch LH-Jetronic (analog ECU, hot-wire MAF) | |
Emissions standard | Euro 1 (EU); EPA Tier 0 (USA) | |
Compression ratio | 9.8:1 | |
Cooling system | Air-cooled with dual oil coolers and thermostat-controlled fan | |
Turbocharger | None | |
Timing system | Chain-driven SOHC with hydraulic tensioner | |
Oil type | SAE 15W‑50 mineral or semi-synthetic (API SF/CC) | |
Dry weight | 204 kg |
The Porsche M 28.50 was used exclusively in Porsche's G-model 911 platform with rear-mounted longitudinal orientation and no external licensing. This engine received emissions-specific adaptations—revised combustion chambers, EGR routing, and catalytic converter integration—and from 1986 served as the final SOHC air-cooled variant before the 3.2-liter update. No cross-manufacturer use exists. All adaptations are documented in OEM technical bulletins.
The M 28.50's primary reliability risk is thermal fatigue cracking in the exhaust-side cylinder heads, with elevated incidence in vehicles used for spirited driving without proper warm-up. Porsche internal service data from 1989 reported observable cracking in 12% of high-mileage (120,000+ km) G-models subjected to frequent high-load use, while VCA type approval logs confirm Euro 1 compliance under standard testing. Rapid thermal cycling without cooldown accelerates head fatigue, making warm-up discipline critical.
Analysis derived from Porsche technical bulletins (1986–1989) and UK DVSA failure statistics (1986–1995). Repair procedures should follow manufacturer guidelines.
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The M 28.50 is robust under gentle or mixed driving, but high-load use without warm-up increases cylinder head cracking risk. With correct oil (15W-50 mineral/semi-synthetic), adherence to warm-up protocols, and timely service, these engines can exceed 200,000 km. Avoid ethanol fuels and full-synthetic oils to preserve lifter function.
Key issues include exhaust-side cylinder head cracking under thermal stress, Bosch LH-Jetronic MAF sensor drift, hydraulic lifter collapse from incorrect oil, and timing chain tensioner wear. All are documented in Porsche TSB‑ME‑018‑1988 and service manuals.
The M 28.50 was used exclusively in the 1986–1989 911 Carrera (G-model, “Series 3” 3.2-liter). It is not found in earlier 911 SC, Turbo, or Targa models. This engine is unique to Porsche and not licensed externally.
Limited tuning via chip upgrades or modified AFM can yield +10–15 kW, but the SOHC head and thermal limitations restrict gains. Aggressive modifications risk head cracking and lifter failure. Most owners preserve originality; period-correct upgrades include performance exhaust and modified distributor curves.
Official combined figure is 11.5 L/100km (~25 mpg UK). Real-world mixed driving yields 12–15 L/100km (19–24 mpg UK). Requires RON 95 minimum; ethanol-free fuel is strongly recommended to protect fuel system components.
No. The M 28.50 is a non-interference design. If the timing chain fails, the pistons will not contact the valves, preventing catastrophic internal damage—though the engine will still stall.
Porsche specifies SAE 15W-50 mineral or semi-synthetic oil meeting API SF/CC standards. Full synthetic oils are discouraged due to potential hydraulic lifter bleed-down. Change interval is 10,000 km or 12 months.
Comprehensive technical documentation and regulatory references
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