The Porsche 911.84 is a 3,299 cc, air‑cooled flat‑six petrol engine produced between 1978 and 1983. It featured a single overhead camshaft per bank (SOHC), Bosch K-Jetronic continuous mechanical fuel injection, and a compression ratio of 9.3:1. Rated output was 162 kW (220 PS) at 5,900 rpm with 280 Nm of torque at 4,800 rpm, engineered for performance under evolving emissions standards.
Fitted exclusively to the Porsche 911 SC (G-Series) for global markets, the 911.84 represented a return to higher performance after the emissions-constrained mid-1970s, balancing drivability with robust air-cooled reliability. Emissions compliance was achieved through K-Jetronic fuel metering, thermal reactors, and revised ignition timing to meet Euro 1-equivalent and US EPA standards.
One documented concern is thermal reactor degradation leading to exhaust backpressure rise, referenced in Porsche Technical Bulletin TSB‑91‑42. This stems from heat-induced cracking in the cast-iron reactors, which restrict exhaust flow and elevate combustion temperatures. Porsche phased out thermal reactors in 1980 for catalytic converter-equipped variants in select markets.
Production years 1978–1983 meet Euro 1-equivalent and US EPA 1978 standards; engine is exempt from modern emissions regulations (KBA Historical Vehicle Registry, Ref. HVR/911/1978).
The Porsche 911.84 is a 3,299 cc air‑cooled flat‑six engineered for the 911 SC (G-Series) (1978–1983). It combines Bosch K-Jetronic mechanical fuel injection with a high-displacement SOHC layout to deliver strong mid-range torque and refined high-rpm performance. Designed to comply with late-1970s emissions mandates, it balances performance with durability through reinforced bottom-end components and revised cooling.
| Parameter | Value | Source |
|---|---|---|
| Displacement | 3,299 cc | |
| Fuel type | Petrol (95–98 RON) | |
| Configuration | Flat‑6 (boxer), SOHC, 12‑valve | |
| Aspiration | Naturally aspirated | |
| Bore × stroke | 95.0 mm × 78.0 mm | |
| Power output | 162 kW (220 PS) @ 5,900 rpm | |
| Torque | 280 Nm @ 4,800 rpm | |
| Fuel system | Bosch K-Jetronic continuous mechanical fuel injection | |
| Emissions standard | Euro 1 equivalent / US EPA 1978 | |
| Compression ratio | 9.3:1 | |
| 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 | 145 kg |
The gear-driven SOHC layout ensures robust high-rpm operation but requires valve clearance adjustment every 10,000 km. Bosch K-Jetronic systems demand precise fuel pressure and clean, dry fuel; control pressure regulator function is critical for smooth warm starts. Air-cooling efficiency depends on full airflow—fan belt tension and cylinder head fin cleanliness are essential, particularly in sustained high-load use. Thermal reactors (pre-1980) restrict exhaust flow and should be inspected for cracking; post-1980 catalytic variants require unleaded fuel only. Use non-detergent mineral oil to protect vintage cam and bearing surfaces.
Oil Specs: Requires non-detergent SAE 20W-50 mineral oil (Porsche 911 SC Owner's Manual, 1979). Modern synthetics may damage vintage seals.
Emissions: Euro 1-equivalent and US EPA 1978 certification applies (KBA Type Approval KBA‑911SC/1978). Thermal reactors on 1978–1979 models; catalytic converters introduced in select 1980+ markets.
Power Ratings: Measured per DIN 70020. Verified in KBA Type Approval KBA‑911SC/1978.
Porsche Technical Service Bulletins: TSB‑91‑01, TSB‑91‑42
Porsche 911 Workshop Manual (1978), Dr. Ing. h.c. F. Porsche KG
Porsche Engineering Report ER‑911/1978
The Porsche 911.84 was used exclusively in the Porsche 911 SC (G-Series) (1978–1983) with rear-engine, rear-wheel-drive mounting and no licensing partnerships. This engine featured platform-specific intake manifolds, reinforced crankshafts, and emissions-specific exhaust systems—and from 1980 catalytic converter-equipped variants replaced thermal reactors in US and select European markets. All adaptations are documented in OEM technical bulletins.
The engine code “911.84” is stamped on the left crankcase flange near the oil filler neck (Porsche TSB‑91‑01). The 911.84 is identifiable by its Bosch K-Jetronic fuel distributor, large-diameter air filter housing, and absence of turbocharging. Engine numbers for this variant begin with “91184*”. Pre-1980 units feature cast-iron thermal reactors on the exhaust manifolds; 1980+ US models use catalytic converters and lack thermal reactors. Do not confuse with the turbocharged 930/60 or earlier 2.7L variants.
The 911.84's primary reliability risk is thermal reactor degradation on 1978–1979 models, with elevated incidence in high-mileage or track-used examples. Porsche internal service reports from 1980 noted cracked reactors in over 30% of early 911 SC units after 80,000 km, while KBA preservation audits identify exhaust flow restriction as a frequent cause of overheating in vintage examples. Sustained high-load operation accelerates thermal fatigue in cast-iron reactors, making inspection critical for performance and cooling integrity.
Analysis derived from Porsche technical bulletins (1978–1983) and KBA historical vehicle audits (2010–2023). Repair procedures should follow manufacturer guidelines.
Find answers to most commonly asked questions about PORSCHE 911-84.
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