Porsche 934

The 934 was the opening salvo in Weissach's unprecented turbo attack on sports and GT competition Total 911 uncovers its full story...

The 934 opened the door for excellence through turbocharging. Here's its story

The man behind Porsche’s first production Turbo, the 930, was Ernst Fuhrmann. His overriding intention was less to introduce a new production model than to go racing: the spur of competition was Porsche’s life blood, and few understood this better than Fuhrmann. FIA rule changes meant that Porsche’s newly acquired turbocharging expertise, brilliantly exemplified by the turbo 917/30’s victories in the 1972-3 Canam championships, now opened a range of opportunities; the 934 would effectively be a 930 built to the new Group 4 GT regulations.

Once the 930 Turbo had been launched the new model was extraordinarily well received despite the prevailing fuel crisis, much to Porsche’s relief. It was apparent by the spring of 1975 that the homologation minimum of 400 units per annum over two years was entirely feasible – in fact Zuffenhausen would consistently outshop over a thousand 930 Turbos a year. The 934 was designed specifically to provide previous 911 RSR clients with a far more powerful entry for the 1976 season in the new Group 4. These would all be client cars. The works team itself would tackle Group 5 and the World Championship for Makes with the silhouette 935.

The FIA ruled that super or turbocharged engines had to meet an equivalence formula, which meant the 934 would have to compete with cars up to 1.4-times its capacity. This put the 934 in the 4 to 4.5-litre class, which dictated a minimum weight of 1,120kg without fuel. Little weight reduction was needed, given the luxuriously specified 930 crossed the scales at only 1,205kg. The cabin was denuded of mats and the seats replaced with a specific bucket for the driver, but the electric windows and door furniture of the 930 remained, a detail which on its own created an amusing historical footnote for the 934. The road car’s bumpers were also retained. With an aluminium roll cage, heavier turbocharger and other modifications which included additional cross bracing in the boot and a 120-litre fuel tank, the 934 weighed in at 1,080kg. That left a margin to bring the car to the minimum weight with ballasting, the positioning of which could be adjusted around the chassis to suit a particular circuit.

The man leading the 934 project was Wolfgang Berger; a chassis engineer, Berger had earned his spurs under Fuhrmann by stripping a 911T shell and modifying it to accept the wider wheels and revised suspension for the proposed Carrera 2.7 RS. For this latest task, Berger would put this accumulation of experience to good effect.

Much of the 930 could be carried over to the 934, and indeed the basis for construction was the stock 930 shell. The original build of the 930 prepared the car to handle far more than the conservative 260bhp of the production model. For example, its suspension with anti-dive geometry at the front suspension, anti-squat of the rear and the heavy-grade wheel bearings had all been calculated with racing in mind: harder springing, solid bushing and different damping characteristics combined with wider tyres were deemed sufficient to bring the road car to competition standard. Group 4 regulations permitted the fitting of auxillary adjustable springing and adjustable anti-roll bars. Steering gear came directly from the production 911, but the brakes, as on the previous 3.0 RSR, came from the

917, their deep-finned calipers instantly recognisable.

The wheels were centre lock. Porsche used its own on the first 934 prototype, and subsequent customer cars wore BBS items; the 934 was also the first 911 to feature 16-inch rims. Berger explains that he was hamstrung by the FIA ruling which said tyres could be of a maximum 14-inch tread width, insufficient for what by 1976 standards was a heavy and powerful (potentially 500hp) car. He solved the problem by getting Goodyear and Dunlop to provide 16-inch diameter rubber which would make both car and tyres more stable. To cover the wheels, which were now 10.5-inch rims at the front and 12-inches at the rear, glass fibre extensions were riveted to the steel wings. Glass fibre was also employed for the front skirt beneath the bumper.

The engine was essentially the 930’s 2,994cc unit with detail changes. The most obvious modifications were a horizontal rather than vertical engine fan and the provision of a water-cooled intercooler. This was built into the rear spoiler, which on the 930 contained the air-conditioning radiator. Flow through this intercooler was driven by a pump operated by one of the camshafts, and it circulated its coolant through two radiators in the front skirt. The entire system added only around 20kg, though its labyrinth of hoses earned it the nickname ‘Porsche Water Power Station’. In practice, the intercooler reduced intake air temperature from about 150ºc to 50ºc with appreciable effect (as colder air is denser) on boost pressure. A much larger KKK turbocharger was installed, raising the 934’s boost setting to 1.35 bar compared with the 930’s 0.8 bar. At this level the 934 delivered a dependable 485bhp at 7,000rpm and 588Nm at 5,400 rpm. All this was achieved with the stock 930 crankshaft and casing, single ignition head and standard camshafts and valve timing, with inlet