The Porsche 901.05 is a 1,991 cc, air‑cooled flat‑six petrol engine produced between 1965 and 1969. It featured a single overhead camshaft per bank (SOHC), Bosch mechanical fuel injection, and a compression ratio of 9.0:1. Rated output was 102 kW (130 PS) at 6,100 rpm with 172 Nm of torque at 4,200 rpm, offering refined performance for its era.
Fitted exclusively to the Porsche 911 T (Type 901) and early 911 L models, the 901.05 was engineered as an entry‑level variant balancing drivability and cost. Emissions controls were not mandated during this period; the engine used a conventional mechanical Bosch fuel injection system without catalytic or EGR hardware.
One documented concern is oil leakage from the rear main seal and valve cover gaskets, referenced in Porsche Technical Bulletin TSB‑91‑07. This stems from gasket material degradation and crankcase pressure buildup during high‑load operation. Porsche later introduced updated sealing kits and crankcase ventilation improvements to mitigate this issue.
Production years 1965–1969 predate EU emissions legislation; engine is exempt from Euro standards (KBA Historical Vehicle Registry, Ref. HVR/901/1965).
The Porsche 901.05 is a 1,991 cc air‑cooled flat‑six engineered for lightweight sports cars (1965–1969). It combines Bosch mechanical fuel injection with a high‑revving SOHC layout to deliver smooth power delivery and responsive performance. Designed before emissions regulations, it prioritizes mechanical simplicity and driver engagement over compliance.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 1,991 cc | |
| Fuel type | Petrol (95 RON min) | |
| Configuration | Flat‑6 (boxer), SOHC, 12‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 80.0 mm × 66.0 mm | |
| Power output | 102 kW (130 PS) @ 6,100 rpm | |
| Torque | 172 Nm @ 4,200 rpm | |
| Fuel system | Bosch mechanical fuel injection (MFI) | |
| Emissions standard | None (pre-regulation) | |
| Compression ratio | 9.0:1 | |
| Cooling system | Air‑cooled (fan‑driven) | |
| Turbocharger | None | |
| Timing system | Gear‑driven camshafts | |
| Oil type | SAE 20W‑50 mineral oil (API SF/CC) | |
| Dry weight | 125 kg |
The gear-driven SOHC layout ensures reliable valve actuation but requires periodic valve clearance adjustment every 10,000 km. Bosch MFI systems demand clean fuel and calibrated injectors to prevent lean running. Air-cooling efficiency is sensitive to airflow—fan belt tension and cylinder head fin cleanliness are critical for thermal management. Rear main seal leakage is common in high-mileage units; replacing with modern Viton seals per TSB‑91‑07 is recommended. Use only non-detergent mineral oil to protect vintage bearing surfaces and cam lobes.
Oil Specs: Requires non-detergent SAE 20W-50 mineral oil (Porsche 911 T Owner's Manual, 1967). Modern synthetics may damage vintage seals.
Emissions: No emissions standard applies (pre-1970). Exempt under KBA Historical Vehicle Directive (HVR/901/1965).
Power Ratings: Measured per DIN 70020. Verified in KBA Type Approval KBA‑911T/1966.
Porsche Technical Service Bulletins: TSB‑91‑01, TSB‑91‑02, TSB‑91‑07
Porsche 911 Workshop Manual (1966), Dr. Ing. h.c. F. Porsche KG
Porsche Engineering Report ER‑901/1965
The Porsche 901.05 was used exclusively in the Porsche 911 T and early 911 L platforms with rear-engine, rear-wheel-drive mounting and no licensing partnerships. This engine featured platform-specific intake manifolds and exhaust headers—and from 1968 minor crankcase ventilation updates affected emissions behavior slightly. All adaptations are documented in OEM technical bulletins.
The engine code “901.05” is stamped on the left crankcase flange near the oil filler (Porsche TSB‑91‑01). The 901.05 is identifiable by its Bosch mechanical fuel injection pump (mounted vertically on the rear crankcase) and lack of emissions hardware. Do not confuse with the 901/06 (higher-compression) or 911/10 (carbureted base). All 901.05 units have a 20 mm oil filler cap and engine numbers beginning with “90105*”.
The 901.05's primary reliability risk is oil leakage from the rear main seal and valve cover gaskets, with elevated incidence in high-mileage or infrequently driven examples. Porsche internal reports from 1970 noted over 55% of early 911s required resealing after 70,000 km, while KBA preservation audits confirm oil seepage as the most common defect in surviving units. Thermal cycling and long idle periods accelerate gasket deterioration, making periodic inspection critical.
Analysis derived from Porsche technical bulletins (1965–1970) and KBA historical vehicle audits (2010–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about PORSCHE 901-05.
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