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 Carrera (G-model “Series 3”) and select 912E variants in limited markets, the M 28.50 was engineered for improved emissions compliance and drivability over its predecessors. Emissions control was achieved through a three-way catalytic converter, exhaust gas recirculation (EGR), and precise lambda control, meeting Euro 1 standards in European markets and U.S. EPA Tier 0 requirements.
One documented concern is thermal fatigue cracking in the exhaust side of the cylinder heads under sustained high-load conditions, highlighted in Porsche Technical Service Bulletin TSB‑ME‑018‑1988. This stems from elevated combustion temperatures in the modified combustion chamber design required for catalytic converter compatibility.
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 SOHC flat-six offers linear power delivery and classic air-cooled character but demands strict adherence to warm-up protocols to prevent thermal shock. Mineral or semi-synthetic 15W-50 oil is critical for lifter and bearing longevity due to the engine’s metallurgy and tolerances. Vehicles used for spirited driving should allow 3–5 minutes of low-RPM warm-up before high-load operation to reduce cylinder head thermal stress. Exhaust-side head cracking is a known risk under track use; visual inspection of the exhaust port bridges is recommended at 100,000 km intervals per TSB‑ME‑018‑1988. Ethanol-blended fuels should be avoided to protect rubber fuel lines and the MAF sensor.
Oil Specs: Requires SAE 15W-50 mineral or semi-synthetic oil meeting API SF/CC (Porsche Lubricants Manual LUB‑1986). Full synthetics not recommended due to lifter bleed-down risk.
Emissions: Euro 1 certification applies to EU-market 1986–1989 models (VCA Type Approval #VCA/EMS/2105). U.S. models meet contemporaneous EPA Tier 0 standards.
Power Ratings: Measured under DIN 70020 standards. Requires RON 95 minimum fuel (Porsche PT‑1987 Datasheet).
Porsche Technical Information System (TIS): Docs G911‑M28‑01, G911‑TIMING‑05, TSB‑ME‑018‑1988
VCA Type Approval Database (VCA/EMS/2105)
DIN 70020: German engine power measurement standard
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.
Locate the engine code stamped on the right rear crankcase near the oil pressure sender (Porsche TIS G911‑ID‑04). The engine number prefix for M 28.50 is '62B'. Visual identification: black anodized valve covers with 'Porsche' script, Bosch LH-Jetronic ECU mounted in the front luggage compartment, and dual-outlet exhaust manifolds feeding a single catalytic converter. Critical differentiation from earlier M 28 variants: M 28.50 uses a modified head casting (part #911.101.073.01) with smaller combustion chambers and EGR ports. ECU label: Bosch 0 280 001 135.
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.
Find answers to most commonly asked questions about PORSCHE M-28-50.
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