The Porsche 911.04 is a 1,991 cc, flat‑six (horizontally opposed) naturally aspirated petrol engine produced between 1966 and 1967. It powered the base-model Porsche 911, serving as the production successor to the short-lived 901.01 after Peugeot’s naming objection. Featuring an air‑cooled design, single overhead camshafts per bank (SOHC), and dual carburetors (Solex 40 PII-4), it delivered 110 PS (81 kW) at 6,000 rpm and 158 Nm of torque. This engine prioritized mechanical simplicity and drivability for road-focused use.
Fitted to the 1966–1967 Porsche 911 (non-S, non-T), the 911.04 was engineered for balanced performance, touring comfort, and everyday reliability. Emissions compliance was not regulated during this era, and the engine relied on proven carbureted induction and air-cooling for consistent operation across varied climates and driving conditions.
One documented engineering update is the standardization of the 911 designation across all variants following the legal naming dispute with Peugeot. Highlighted in Porsche Internal Memo IM-66-901, this resulted in renumbering all 901-series engines to the 911-series without mechanical changes. The 911.04 retained the original 1,991 cc SOHC architecture but benefited from minor production refinements in cylinder head porting and ignition timing versus early 901.01 units.
The 911.04 predates EU emissions regulations and was not type-approved under modern frameworks (VCA/EU).
The Porsche 911.04 is a 1,991 cc flat‑six air‑cooled petrol engine engineered for entry-level sports coupés (1966–1967). It combines SOHC valvetrain architecture with twin Solex carburetors to deliver responsive throttle response and accessible performance. Designed before emissions regulation, it prioritizes mechanical reliability and driver engagement.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,991 cc | |
| Fuel type | Petrol (Gasoline) | |
| Configuration | Flat‑6 (horizontally opposed), SOHC, 12‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 80.0 mm × 66.0 mm | |
| Power output | 81 kW (110 PS) @ 6,000 rpm | |
| Torque | 158 Nm @ 4,000 rpm | |
| Fuel system | Twin Solex 40 PII-4 carburetors | |
| Emissions standard | Not applicable (pre-regulation era) | |
| Compression ratio | 9.0:1 | |
| Cooling system | Air‑cooled (fan‑driven) | |
| Turbocharger | None | |
| Timing system | Chain-driven camshafts (dual chains) | |
| Oil type | SAE 20W-50 mineral oil (API SC/SD) | |
| Dry weight | 175 kg |
The carbureted SOHC flat-six offers forgiving drivability and mechanical transparency but requires valve clearance adjustment every 10,000 km and carburetor synchronization every 15,000 km to maintain smooth idle and throttle response. Use of leaded-equivalent additives is strongly advised with modern unleaded fuel unless hardened valve seats are installed. Chain tensioners must be inspected for wear; early 911.04 units share the same chain system as the 901.01 and are susceptible to guide rail degradation under extended oil change intervals. Air-cooling demands adequate airflow—avoid prolonged idling in traffic to prevent overheating.
Oil Specs: Requires SAE 20W-50 mineral oil meeting API SC/SD (Porsche Lubrication Bulletin LB-1966-01). Zinc-rich formulation essential for flat-tappet cam protection.
Emissions: Not subject to emissions regulation (pre-1970 EU framework). Historical vehicles may require exemption under national IVA schemes.
Power Ratings: Measured under DIN 70020 standards. 110 PS rating verified by Porsche Factory Performance Data Sheet FPD-1966-B.
Porsche Classic Technical Archive: Docs PCA-TA-911-66, ER-1966-F6B
Porsche Workshop Manual 911 (1966 Edition)
Porsche Factory Performance Data Sheet FPD-1966-B
EU Regulation (EC) No 715/2007 – Annex I Scope Definition
The Porsche 911.04 was used exclusively in the Porsche base-model 911 with rear‑engine, longitudinal mounting. This entry-level variant provided core 911 driving dynamics without the performance enhancements of the S or T models. No cross‑manufacturer or platform sharing occurred. All revisions are documented in Porsche engineering bulletins.
The 911.04 engine number is stamped on the right-side crankcase near the flywheel housing (Porsche Workshop Manual 911, p. 12). Units begin with '91104' followed by a sequential number above 250. Critical visual identifiers: twin Solex 40 PII-4 carburetors with individual air filters, and absence of fuel injection hardware. Differentiate from 901.01 by engine code stamping and from 911S (901.08) by SOHC (single cam tower per bank) and lack of DOHC valvetrain. Engine type is also recorded on the vehicle’s Kardex card under “Motorbezeichnung.”
The 911.04's primary reliability considerations are valve seat recession under unleaded fuel, carburetor imbalance, and timing chain tensioner wear. Porsche’s internal durability logs from 1967 showed good longevity under period-correct fuel and maintenance, but modern operation without upgrades increases wear risk. Cold-engine stress and ethanol-blended fuels accelerate gasket and carburetor degradation.
Analysis derived from Porsche technical bulletins (1966–1968) and EU historical vehicle documentation (2010–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about PORSCHE 911-04.
Comprehensive technical documentation and regulatory references
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Regulation (EC) No 715/2007
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Commission Regulation (EU) 2017/1151
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