Porsche 914-6 Conversion Guide: From 914-4 to Flat-Six Power

Porsche 914 Technical Guide

Four to Six

A General Guide to the Porsche 914-6 Conversion

The broad mechanical, structural, cooling, fuel, electrical, and chassis work involved in converting a Porsche 914-4 to six-cylinder power.

For Porsche enthusiasts, the 914 is a unique chapter in the company’s history. Born from a joint venture between Volkswagen and Porsche, the mid-engine platform was praised for its superb, balanced handling. However, the standard Volkswagen-derived Type 4 flat-four engine left many drivers wanting more. Enter the factory 914-6. With a 2.0-liter flat-six borrowed from the previous year’s 911T, the factory six-cylinder car turned the chassis into a genuine sports car icon. Because only 3,351 factory 914-6 models, including the M471 and GTs, were built between 1970 and 1972, acquiring a genuine “-6” is a rare and expensive proposition.

Fortunately, Porsche engineered the 914 chassis with the capacity to accept the larger six-cylinder engine. Converting a 914-4 into a 914-6 is one of the most rewarding mechanical transformations an owner can undertake. Relying on classic documentation and decades of collective wisdom, this article outlines the broad mechanical, structural, and electrical steps required to swap a flat-six into a four-cylinder chassis.

Planning and Engine Selection

Before turning a single wrench, you must select your powerplant. While a factory 914-6 used a 2.0L Type 901/36 engine, builders today use everything from early 2.0L engines to 3.6L engines from later 911s.

Your choice dictates the complexity of the conversion:

  • Early engines, 2.0L to 2.7L: Often carbureted with Weber 40 IDA or PMO carburetors, these engines match the vintage aesthetic and require less complex electrical wiring.
  • Later engines, 3.0L to 3.6L: These offer substantial power increases but bring additional weight, a potential need for electronic fuel injection (EFI) or Bosch Motronic wiring, and higher torque demands that will test the structural integrity of your transmission and chassis. Of this group, the 3.0 911SC engine is our favorite by far. The crank journals increased in size on the 3.2 and 3.6 variants, causing a lower red line RPM. The 3.0 is the most “bullet-proof” engine you can get in this range.

The Dry-Sump Oil System and Auxiliary Cooling

Unlike the wet-sump Type 4 engine, Porsche flat-six engines use a dry-sump lubrication system that requires an external oil tank. Managing this plumbing and providing adequate thermal control can be the most labor-intensive part of the swap.

Benefits: Retains roughly 75% of the front-trunk space, follows a factory-authentic layout, improves cooling, creates effective inlet and outlet pressure zones, and stiffens the front end.

Tradeoffs: The cost can be higher than a home-built setup. The improved cooling may also leave you with an excessive amount of free time to obsess over parts of the build other than oil temperature.

Sheet Metal, Engine Tin, and Exhaust

Just like the original Type 4 four cylinder engines, a flat-six engine requires controlled airflow across its finned cylinders. This is one of the areas where you can't skimp.

  1. Install six-cylinder engine tin: A five-piece 914-6 engine sheet-metal kit seals the engine perimeter against the chassis walls, separating hot exhaust air below from cool intake air above. An incomplete seal allows the cooling fan to recirculate hot air and can cause overheating. Our friends at Restoration Design make an exact duplicate of the factory engine tin.
  2. Address the rain tray and engine lid: The factory 914-4 uses a plastic rain tray beneath the engine-lid mesh. On a six-cylinder conversion with carburetors or tall intake runners, the tray interferes with the air cleaners and must be removed. A quality factory 911 or 914-6 air-cleaner assembly handles wet-weather duty. Other common alternatives are the now famous PMO "Watershed" air filters.
  3. Use 914-6-specific exhaust components: Standard 911 headers do not fit a 914 because of the mid-engine configuration with the rear suspension-console and transmission in the way. 914-6-specific headers or heat exchangers are a must. The exhaust terminates in a 914-6-muffler that exits through the left side of the rear valance. There are multiple mufflers available with dual outlets on the sides or, for a more sporty look, you can go after the factory GT look with dual tips out a more central location.

Actual factory-style 914-6 mufflers are difficult to source from almost all current suppliers. Plan on cutting and repositioning the outlet tip so it aligns perfectly with the valance. Original metal 914-6 rear valances are also rare. Fiberglass replacements are available for a factory-style appearance, but they commonly require fitting and finishing work.

Fuel Delivery and Mechanical Linkages

The fuel system requires major changes when moving from the electronic fuel injection of a 914-4 to the fueling needs of a flat-six.

  1. Fuel pump and pressure: Carbureted engines cannot use the high-pressure pump from the Bosch D-Jetronic or L-Jetronic four-cylinder system, which operates at roughly 30 PSI or more. Replace it with a low-pressure, high-volume pump operating at approximately 3.5 to 4.0 PSI. For safety and reduced vapor-lock risk, mount the new pump beneath the front fuel tank rather than in the engine bay. PMB uses the later 1975–1976-style fuel-pump cover and mount remanufactured with Restoration Design before its builds go to paint. View PMB’s preferred 3.5–4.0 PSI fuel pump.
  2. Throttle linkage: The four-cylinder throttle-cable pull differs from the six-cylinder arrangement. Carburetors or electronic fuel injection require a 914-6-style bellcrank linkage on the side of the transmission intermediate plate. A bolt-on throttle bellcrank kit can adapt the factory four-cylinder pedal assembly to operate the six-cylinder linkage smoothly. View the throttle bellcrank kit.

Bringing the Porsche 914-6 Conversion Together

Converting a 914-4 to a 914-6 is a meticulous project that transforms an excellent vintage momentum car into an aggressive, visceral sports car. A methodical approach to the engine mount, dry-sump plumbing, engine cooling, drivetrain, and braking can produce a reliable machine that honors Porsche’s engineering philosophy.

For detailed plumbing schematics, wiring diagrams, component guidance, and help keeping the project on track toward its first drive, contact the knowledgeable team at PMB Performance.