02 / ENGINEERING
A flat-six, air cooling and Bosch mechanical fuel injection.
Explore mechanical injection →
The 1973 model year was the last for the original 911 generation. The S retained the long hood and slender bumpers, with a 2.4-litre flat-six at the back.
The S combined mechanical fuel injection with a five-speed gearbox and a front spoiler shaped by lessons from the racetrack. With peak power of 190 PS at 6,500 rpm, the engine rewards using the gears.
The 2.4 S, by the numbers: Porsche’s period specification.
Three cylinders sit on each side of the crankshaft, facing those on the opposite side. This horizontally opposed arrangement gives the flat-six its name and keeps the engine’s mass low. Mounted behind the rear axle, it puts weight over the driven wheels and gives the 911 its distinctive balance.
A fan sends air over the finned cylinders and cylinder heads, carrying heat away without a conventional water-cooling circuit. Engine oil plays an important role in managing heat, too. The fan, valves and exhaust all contribute to the early 911’s unmistakably mechanical soundtrack.
The 2.4 S’s front spoiler grew out of Porsche’s aerodynamic work and helped directional stability at speed. The five-spoke Fuchs wheel design has its own S heritage: forged alloy Fuchs wheels first appeared on the 1967 model-year 911 S. Slender bumpers and the long hood complete the early silhouette.
Porsche: the flat-engine tradition
Porsche: the 2.4 S, its engine and front spoiler
Porsche Classic: 2.4 S power and mechanical injection
Porsche: the Fuchs wheel story
DESIGN & DEVELOPMENT / 1963–1973
Follow the original 911’s development from F. A. Porsche’s first proposals to the longer wheelbase and the 2.4-litre S, with period road tests and owners’ perspectives.
Explore the original 911’s design and evolutionWhy enthusiasts love MFI.
Ask an early 911 enthusiast about mechanical fuel injection and the conversation soon turns to feel: the eager response to a small movement of the pedal, the intake sound, the pleasure of letting an S engine climb through its rev range.
Camshafts, airflow, ignition and exhaust work with the injection system to shape the way an S engine delivers its power.
A fuel map
you could hold
in your hand.
The Bosch pump meters fuel mechanically. A contoured, three-dimensional “space cam” helps translate engine speed and accelerator position into the required delivery. Its shape serves as a physical fuel map. Separate mechanisms compensate for warm-up and atmospheric pressure.
Each cylinder has its own throttle butterfly. Linkages coordinate those throttles with the injection pump, so airflow and fuel delivery rise together as the pedal moves. Synchronizing them gives each cylinder the airflow it needs for smooth, even running.
Porsche’s factory approach was “Check, Measure, Adjust”: establish the engine and ignition fundamentals, check injection timing and linkage, synchronize the throttles, then measure the mixture. Each adjustment depends on getting the preceding checks right.
Porsche’s Mechanical Fuel Injection: Check, Measure, Adjust (archived factory booklet) explains the operating system and tuning sequence.
An owner discussion on Pelican Parts captures the enthusiasm for a properly sorted MFI engine.
Black Forest’s Bosch pump workshop offers a closer look at the restoration and calibration craft.