During the 1974 and 1975 seasons, Porsche’s 3.0-litre 911 Carrera RSR reigned supreme in international GT competitions, helping Weissach to titles on both sides of the Atlantic. During each year of its tenure as the top racing 911, the 3.0 RSR secured both World Championship and European GT honours, while Stateside a similar feat was achieved in the Trans-Am and IMSA GT series. The naturally aspirated car was, therefore, no slouch in the hands of both seasoned professionals and the numerous privateers who campaigned them around the world. However, for the 1976 season, Porsche had a new ace up its sleeve: the 934.
In January, Weissach’s valued customers were invited to the Nürburgring to watch Porsche’s latest GT contender in action. At the helm of the prototype was test driver, Manfred Schurti, a man no stranger to success behind the wheel of 911s having won the GT class at the 24 Hours of Le Mans just six months prior. When Schurti stopped the stopwatch, the order books opened with most of the established teams switching to the new car. Why? The Liechtensteiner had lapped the Nürburgring 15 seconds faster than the outgoing 3.0 RSR.
The CSI’s decision to delay the introduction of the revised Group 4, 5 and 6 regulations, originally planned for 1975, until the start of the following season had allowed Porsche to use the newly introduced 930 road car as the basis for its latest GT racer, with the 911 Turbo’s production figures more than satisfying the Group 4 rule book’s stipulation that at least 400 examples needed to have been built in a two-year period. The 934 (so named because it was a Porsche 930 built to Group 4 specification) was more closely related to the road car than its silhouettestyle brother, the 935. Led by Wolfgang Berger – the man who oversaw the 2.7 RS project – development of the 934 began in earnest in May 1975 and they soon found the restrictive rule book a problem. The larger-than-standard KKK turbocharger in the 934’s 930/71 flat-six engine generated a lot of heat, especially when run at the maximum boost pressure of 1.4 bar.
At these speeds, the red-hot turbo would heat the inducted air to around 150 degrees Celsius (300 degrees Fahrenheit), reducing the charge’s power and increasing the likelihood of the fuel pre-detonating. What was needed was an intercooler but, unlike the Group 5 rules, the limitations on aerodynamic development in Group 4 required Porsche to use the standard decklid from the road car. While the whaletail wing may have looked cool (and provided more downforce than the old ducktail design), it didn’t leave enough space for the large air-to-air intercooler used on the Carrera RSR Turbo 2.1 in 1974. Weissach’s engineers went back to the drawing board to see what could be done and soon found a way of mounting two Behr air-to-water intercoolers (one for each bank of cylinders). Unlike the 935 – which was soon fitted with those sloping flatnose fenders – the 934 had to use the idiosyncratic upright front wings, yet under the centre line of the front wheels there was more freedom, allowing an aggressive air dam chin splitter to be fitted (although the impact bumpers, complete with concertinas, had to be retained). The intercoolers improved the charge density drastically, reducing the intake temperature to 50 degrees Celsius (120 degrees Fahrenheit).
The design also improved front downforce and helped to feed fresh, cooling air to the brakes, as well as accommodating an oil cooler. Inside the 2,994cc flat six, the rule book again dictated much of the specification. The crankcase, crankshaft, con-rods and cylinder heads were identical to the 930/50 engine used in the 911 Turbo, the car used to homologate the 934. Although new pistons were fitted, the compression ratio remained at 6.5:1, but Hans Mezger and Valentin Schäfer were able to fit larger intake and exhaust valves (seated above 41mm ports). The talented engineers were also allowed to fit more aggressive camshafts and a revised Bosch K-Jetronic electronic injection system.