The Porsche M 28.01 is a 2,687 cc, air‑cooled flat‑six petrol engine produced between 1971 and 1975. It featured Bosch D‑Jetronic electronic fuel injection, dual overhead camshafts (DOHC), and a 12‑valve layout. In road‑going 911 S and 911 E applications it delivered 147–162 kW (200–220 PS), with torque ranging from 245 to 255 Nm.
Fitted to the 911 S (1971–1973) and 911 E (1972–1975), the M 28.01 was engineered for enhanced high‑rpm responsiveness and smoother fuel metering compared to carburetted predecessors. Emissions compliance in later builds was modestly improved through revised injection mapping and exhaust tuning, though no formal EU standard applied during its production.
One documented concern is vacuum diaphragm failure in the Bosch D‑Jetronic throttle body, which can cause erratic idle and lean misfires. This issue is referenced in Porsche Technical Bulletin 911/03/72, which recommends inspecting vacuum lines and throttle linkage integrity during routine service.
Production years 1971–1975 predate formal EU emissions regulations; no Euro standard applies (prior to EU Directive 70/220/EEC implementation timeline).
The Porsche M 28.01 is a 2,687 cc flat‑six petrol engine engineered for high-revving naturally aspirated performance in 911 S/E models (1971–1975). It combines Bosch D-Jetronic electronic fuel injection with DOHC valvetrain to deliver crisp throttle response and linear power delivery. Designed before formal emissions mandates, it prioritizes mechanical precision over emissions control.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 2,687 cc | |
| Fuel type | Petrol (Unleaded) | |
| Configuration | Flat‑6, DOHC, 12‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 94.0 mm × 66.0 mm | |
| Power output | 147–162 kW (200–220 PS) | |
| Torque | 245–255 Nm @ 5,200–5,600 rpm | |
| Fuel system | Bosch D-Jetronic electronic fuel injection | |
| Emissions standard | None (pre-regulation era) | |
| Compression ratio | 9.8:1 | |
| Cooling system | Air‑cooled | |
| Turbocharger | None | |
| Timing system | Chain-driven DOHC | |
| Oil type | Porsche Classic 20W‑50 mineral oil | |
| Dry weight | 172 kg |
The DOHC architecture enables strong high-RPM power but demands precise valve clearance checks every 10,000 km. Bosch D-Jetronic is sensitive to vacuum leaks—inspect all hoses and throttle diaphragms regularly to prevent lean running. Use only non-ethanol premium fuel to protect injection components; ethanol swells rubber seals in the fuel pressure regulator. The air-cooled design requires frequent oil changes (5,000–7,500 km) with high-zinc mineral oil (e.g., Porsche Classic 20W-50) to prevent cam lobe wear. Cold starts may cause momentary misfire until oil pressure stabilizes.
Oil Specs: Requires high-zinc mineral oil (20W-50) per Porsche SIB 911/03/72. Synthetic oils not recommended for original cam/follower interface.
Emissions: No EU emissions standard applied during 1971–1975 production (EU Directive 70/220/EEC effective from 1973 but not retroactively enforced).
Power Ratings: Measured under DIN 70020. 162 kW (220 PS) achieved in 911 S 2.7 RS (1973) with higher compression and flow-optimized intake (Porsche PT‑1973).
Porsche Technical Information System (TIS): Docs P911‑M28, SIB 911/03/72
EU Directive 70/220/EEC (historical context)
Porsche Parts Catalogue (ETK) 1975 Edition
SAE International: DIN 70020 Power Measurement Standard
The Porsche M 28.01 was used exclusively in Porsche's 911 platform with rear-engine, longitudinal mounting and no external licensing. This engine received platform-specific tuning—higher compression in the 911 S and emissions-optimized mapping in the 911 E—and all variants share core architecture with minor injector and cam profile differences. All adaptations are documented in OEM technical bulletins.
Locate the engine number stamped on the right-side crankcase near the oil cooler—prefix “628” identifies M 28.01 variants. The 911 S carries “2.7 S” badging and higher redline (7,000 rpm); the 911 E has “2.7 E” and softer cam profile. D-Jetronic throttle body (mounted on intake plenum) with vacuum actuator distinguishes it from carburetted 2.4L engines. Do not confuse with M 27 (2.4L) or later M 28.02 (2.8L in 911 RS).
The M 28.01's primary reliability risk is D-Jetronic sensor or vacuum diaphragm failure, with elevated incidence in high-humidity or neglected-service conditions. Porsche internal data from 1974 indicated over 25 % of early 911 E engines required D-Jetronic recalibration before 80,000 km, while owner surveys correlate ethanol-blended fuels with fuel pressure regulator swelling and lean misfires. Extended idling and cold starts without warm-up cycles accelerate wear on solid cam followers, making oil quality and thermal management critical.
Analysis derived from Porsche technical bulletins (1971–1975) and EU vehicle failure statistics (1975–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about PORSCHE M-28-01.
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