Guide: Porsche 911 2.7 Carrera Turbo
Background
As the Porsche 911’s rivals were mostly larger-engined models, by the early 1970s it was obvious that more power would have to be extracted from the air-cooled Flat-6 engine if it was to remain competitive on road and track.
Substantially enlarging the engine was not an option as the 911’s layout already had its handling idiosyncrasies: to add more weight behind the rear axle would only exacerbate the issue.
Instead, the solution was turbocharging, something Porsche became an early proponent of in motor racing.
After dominating the Can-Am championship with the spectacular forced induction 917/10 and 917/30 between 1972 and 1973, Porsche switched focus and campaigned a batch of experimental 911 Carrera RSR Turbos throughout 1974.
These Martini-backed 2.2-litre test beds ran in the prototype class of the World Sportscar Championship which allowed the utmost freedom of development. The successful 1974 campaign provided Porsche with much of the knowledge they needed to release a forced induction road car into circulation.
The first road-going 911 Turbo was not the familiar 930 that entered production in February 1975. Nor was it the engine-less prototype that had appeared at the Paris Motor Show in October 1973.
Instead, it was a one-off narrow-bodied mule that was subsequently gifted to Ferry Porsche’s sister, Louise, on her 70th birthday in August 1974.
Built on chassis 9115600042, this 2.7 Carrera Turbo also pre-dated the prototype 930 that was shown in almost production-ready guise at the Frankfurt Motor Show in October 1974.
Chassis
It was based on a standard early 1975 model year Carrera 2.7 equipped with the usual all-round independent suspension, ventilated disc brakes and 15-inch Fuchs alloy wheels (6-inches wide at the front, 7 inches wide at the rear).
Engine & Gearbox
Although precise details of the original 2.7-litre engine installed in the car were never publicly revealed, we do know this experimental unit had a single turbocharger and Bosch K-Jetronic with the CIS injection system as opposed to the MFI arrangement found on the stock 2.7 Carrera.
Displacement was unchanged from the normally aspirated version: 2687cc thanks to a bore and stroke of 90mm and 70.4mm respectively.
The compression ratio, power output and torque rating were never published but approximately 240bhp was quoted by factory insiders.
This was transmitted through a four-speed 915 gearbox with special ratios and a limited slip differential.
The combination of massive torque and the potential to strip gears meant a factory five-speed 911 Turbo wasn’t offered until the 1989 model year. By this time, the 915 ‘box had been replaced with Porsche’s uprated G50 unit.
Bodywork
From the outside, nothing suggested the 2.7 Turbo was anything out of the ordinary. It used a standard narrow body pre-930 shell which was still badged as a Carrera.
The silver prototype came with headlight washers and a driver’s side door mirror.
Weight / Performance
Weight was 1084kg and, thanks to an excellent power-to-weight ratio, the car would have delivered similar performance to a normally aspirated 2.7 Carrera RS.
Interior
Initially, the black interior only sported a non-standard 10,000rpm tachometer.
Modifications
After chassis 5600042 had completed its development programme, Porsche carried out a number of modifications ahead of the car’s handover to Louise Piech.
The changes included new red leather upholstery with red and blue MacLaughlan tartan seat centres and matching door cards. Fresh red carpet and a black headliner were installed along with a Blaupunkt four-speaker stereo plus electric antenna and a voice recorder.
Outside, tartan side decals matched the seat centres.
Soon afterwards, front and rear spoilers were added whilst, for practicality, the experimental engine was replaced with a standard three-litre turbocharged motor from the 930.
Subsequent History
In this configuration, the car was presented to Louise Piech on August 28th 1974.
Chassis 5600042 was retained by the Porsche family and now resides in the factory museum.
Text copyright: Supercar Nostalgia
Photo copyright: Porsche - https://www.porsche.com
