PLASTIC FANTASTIC
Thereʼs an old adage in the motor industry that goes something like ʻwin on Sunday, sell on Mondayʼ. It could have been written for Porsche which had built its reputation on race victories – both class and outright – since the very early 1950s. The 904 GT
We raid Porsche’s archives to bring you the story behind the 904 GTS
In the early 1960s, Porsche had concentrated on two principal arenas of motorsport: Grand Prix – with singleseaters in both Formula One and Formula Two – and the new GT (Grand Touring) championship. In the latter, it was the two-litre class which held the most interest. Indeed, Porsche won the 2.0-litre GT championship in 1961 with the Abarth-carrera GTL, powered by the venerable Furhmanndesigned four-cam engine.
This was no mean feat, for the Porsches were, on paper at least, outclassed, relying as they did on an engine with a swept volume of just 1.6-litres running against opposition fully exploiting the 2.0-litre capacity allowed by the regulations. In 1962, the imbalance was redressed with the introduction of the 1966cc Carrera 2 coupé, which was duly homologated for race use and allowed Porsche to claim the championship once again.
We can probably thank Carlo Abarth for the birth of Porscheʼs 904. No, he didnʼt play any role in its design, nor (as far as we are aware) did he even discuss such a vehicle with Porscheʼs engineers while he was collaborating on the highly successful Abarth-carrera project. Abarth had already won the 1.0-litre GT championship in 1961 with Fiat-based entries, and it soon became clear that he was now setting his sights a little higher.
In 1963, Abarth began work on a new model, the AbarthSimca, a slippery coupé with which he planned to attack the 2.0-litre GT championship. He twisted the knife a little deeper in Porscheʼs side by ʻstealingʼ Hans Herrmann, employing the former Porsche pilot as a test and race driver. Alongside this came news that Alfa Romeo was also setting its sights on the same championship with its new Guilia TZ coupé.
This unplanned pressure brought to bear on Porsche proved to be a blessing in disguise as it meant that the race department at Stuttgart had to step up its game. Forays into the world of Formula One had proved expensive for relatively little return, meaning that questions were asked of the true value to be derived from such a venture. Nobody, however, doubted the worth of racing in the GT championship, using a car that customers could identify with. Like we said at the beginning: win on Sunday, sell on Monday…
But what avenue to follow? Past home-built sports-racing cars such as the Type 718 coupés, as raced at Le Mans in 1961, had been successful ventures but their method of construction – hand-formed aluminium bodies over complex tubular steel chassis – did not lend itself to the new GT rules, which called for a minimum of 100 examples to be built in a 12-month period. Abarthʼs creations were generally rebodied production cars, using the floorpan and basic drivetrain supplied by another company, such as Fiat or, in this instance, Simca.
Porscheʼs ageing 356 did not really lend itself to this method of construction – not if it was to be a race winner. Plans were already well advanced for its replacement – the Type 901 – but that was still some way off production. What Porsche needed was a car that could be built quickly and easily, and at reasonable cost. A car that could be used in multiple motorsport disciplines if the maximum return on the companyʼs investment was to be achieved. With the 901 in the pipeline, the most obvious engine to use would be the all-new six-cylinder engine and matching five-speed transaxle under development for the new model. It was proposed to mount the engine ahead of the transmission, a layout which previously had been the domain of outright sports-racing cars, rather than those which were intended to see road use. It was a decision which attracted considerable interest both within Porsche and among its rivals. It is worth noting at this point that until the advent of the Boxster and its later sibling, the Cayman, Porsche only ever produced one road-legal mid-engined design other than the 904: the Vw-porsche 914.
“WHAT PORSCHE NEEDED WAS A CAR THAT COULD BE BUILT QUICKLY”
The task of designing such a vehicle fell into the hands of Ferdinand Porsche III – better known by all as ʻButziʼ. By his own admission, he was not personally interested in competing, or even test driving Porscheʼs race cars, but he did value the contribution such activities made to the company. According to Karl Ludvigsen in his seminal work Excellence Was Expected, Butzi also welcomed the opportunity ʻto experiment with new body formsʼ.
Butziʼs design for the new sports-racer was quite unlike any previous Porsche. It was very low, at just under 42ins, and as a consequence presented a far smaller frontal area than even the streamlined Abarth-carrera which preceded it: 14.2sq ft compared to 15.4sq ft. The 904 was slightly longer than its predecessors, with a wheelbase set at 90.6ins (2300mm), compared to 82.7ins (2100mm) for the 356 and 718 RSK. The Type 901, for the sake of comparison, had a wheelbase of 87ins (2211mm).
There is little argument about how beautiful the 904 is as a design. Butzi learned a lot about airflow over a midengined car from the old 718 coupé, and incorporated many of its basic design features in to the 904: the long nose, doors which cut into the roofline to ease access, the deep windscreen – all were elements carried over from the 718 coupé. But somehow they all integrated seamlessly in Butziʼs design. It was a classic case of if it looks right, it probably is right.
There were several unique elements which set the 904 apart from other Porsche designs. Principal among them was a strongly defined swage line which ran the full length of the car, from its nose right back to the rear quarters. The line defined the lower edge of the rear body panel, which opened clamshell-fashion to give access to the engine and transmission. The swage line helped to visually lengthen and lower the 904 in profile.
Other features set the 904 apart. At the front, a wide, flat ʻboot lidʼ opened to give access to the fuel tank and brake reservoirs, while long Plexiglas covers protected the headlights and helped give the car a very sleek look. At the rear, a flicked-up tail panel was in stark contrast to the long overhang at the front. Hella supplied the round light units used at the front and rear for turn signal, side/tail and brake lights, these also forming part of the defining character of the 904.
There was one other significant design element: the roof. This was a buttressed design, with sail panels on each side flowing smoothly into the rear quarters, with a flat panel above the mid-mounted engine. In the upper B-panels behind the doors, slatted air scoops were fitted – but not, it should be noted, to the very first of the three prototypes.
As noted by Ludvigsen, Porsche had of late shied away from spending time with its race cars in the wind tunnel – arrogance on the part of the designers, or simply a case of saving time and money? In the case of the 904, that is neither here nor there, for later tests showed that Butziʼs slippery design had a coefficient of drag of just 0.33 – an impressive figure by the standards of the time.
What really set the 904 apart was the decision to mould the body from GRP – glass-reinforced plastic, or glassfibre as it is more widely known. This decision was largely driven by technical director Hans Tomala who had gained experience with the material on Porsche's Grand Prix cars and the W-RS roadster. In both cases, glassfibre panels had been used in a non-structural manner, but for the new project, Tomala saw the benefits of using glassfibre as an efficient way to increase its torsional strength.
Tomalaʼs idea was to build a perimeter chassis, fabricated from steel components which were then welded together to form a rigid structure. By itself, the 904ʼs chassis was more resistant to twisting than the 356ʼs substructure, which had formed the underpinnings of the Abarth-carrera, but Tomala wanted to take things a stage further by bonding the chassis to the body so they became as one. It was a novel idea and which worked well, even if many years down the road it would prove to be the bane of restorers who struggled to repair rusted chassis members.
A preliminary buck was made from wood and resin filler in the Porsche workshops from which a set of female moulds could be taken. But who to entrust the task of laying up the glassfibre bodyshells and allied panels? This task fell on a name which will be familiar to aviation enthusiasts – especially those with an interest in World War II aircraft: Heinkel.
Ludvigsen describes the construction of the body in some detail: ʻ(Heinkel) hand-laid the 904ʼs skin to a 2mm thickness. They built it up of three layers of glassfibre, one woven and two in mat form, impregnated with a BASF polyester resin tradenamed Palatal. The main fixed body parts, the underbody, cockpit interior and roof, were bonded to each other and around the frame, which had previously been coated with a special paint to strengthen the bondingʼ.
The chassis itself was fabricated in-house at Porsche and comprised a pair of box-section members running down each side of the bodyshell. These side members were formed from
“A PRELIMINARY BUCK WAS MADE FROM WOOD AND RESIN…”
channel sections which were closed off with corrugated steel strips spot-welded in place. Cross-members were located under the cockpit and supplemented by a pair of hoops, which acted as open bulkheads at the front and rear of the chassis.
The combined body/chassis structure weighed a little over 135kg (300lbs) and proved to be 50 per cent more rigid than the aluminium-bodied Abarth-carrera, and stiffer, too, than the 356C coupé which was then in production.an added benefit, as pointed out by Ludvigsen, the whole structure became even more rigid as the GRP moulding ʻagedʼ.
But what of the drivetrain? The gearbox was to all intents and purposes the same unit which would see service in the forthcoming 901 which, of course, would not go into production until the following year. It was a five-speed unit based around a tunnel-style transmission casing and featured a ZF limited-slip differential unit. This was a new design using clutches rather than the old ZF unit, which was a pre-war design relying on a sliding-cam system. The driveshafts were of the Nadella type, as used on the first 911s and 912s.
The 904 had been designed from the start to use the new six-cylinder engine destined for the 901, but time ran out. There was no way by mid-1963 that the six would be ready, so the decision was made to use a revised version of the Type 587/2 2.0-litre four-cam engine which had originally seen such sterling service in the Abarth-carrera and the Carrera 2. With just 155bhp available, there was concern that the venerable four-cam might not be up to the job of allowing the 904 to see off new opposition from Alfa Romeo and Abarth (with the new Simca-based coupé).
Hans Mezger was the man who took care of this ʻdeficiencyʼ, increasing the size of both inlet and exhaust valves, as well as making changes to the camshaft timing as well as increasing duration and valve lift. Weber 46IDM carburettors allowed the engine to breath at the higher rpm it was now able to operate. However, increased engine speeds would place greater strains on the bottom end, so Mezger redesigned the conrods and also increased the diameter of the crankcase through bolts. Oil passages within the crankcases were also enlarged to provide a greater flow of oil to the bearings.
With new Ferral-coated aluminium cylinders, the Type 587/3 engine was rated at 180bhp at 7200rpm, and 145lb ft of torque at 5000rpm. These were the figures attained with the competition exhaust system, the barely-muffled ʻroad-legalʼ set-up capping the outputs at 155 and 124 respectively.
Three prototypes were built, the first of which is distinguishable by the lack of intake vents behind the doors.
The bodies were unpainted, save for a coat of primer. As work was still progressing on the revised engine, each of the prototypes was powered by the old Type 587/2 engine from the Abarth-carrera. The first tests were carried out late in August 1963 at Weissach, with further more extensive tests held at the Nürburgring and Hockenheim.
The new transmission proved to be a weak link in the 904ʼs chain, with the new ZF limited-slip differential being one source of problem, along with broken mountings, oil leaks and poor shifting. These failures highlighted a problem with the design of the rear of the 904ʼs chassis when it was discovered that it was only possible to work on the transmission (specifically, change gear ratios) with it removed from the car. By redesigning the tail end of the chassis, it would in future be possible to remove the rear of the transmission casing and carry out ratio changes with the gearbox in the car.
The plans was to build the 100 examples necessary to satisfy the entry requirements for the GT championship, with the 1964 season being the target. In November 1963, Heinkel delivered the first body and chassis units ready for production, while that same month, Herbert Linge took one of the three prototypes back to the Nürburgring to assess the various revisions which had been made following those preliminary test sessions in the summer. With a lap time of around 9mins 30secs, everyone was happy for the press to meet the new baby.
The press launch was held at the Solitude circuit, just outside Stuttgart, at the end of November where it was announced that the new car would be offered for sale at a price of DM29,700, compared to DM23,500 for a Carrera 2. It was also announced that it would be powered by the Type 587/3 four-cylinder engine and, significantly, that the new ʻsixʼ would not be available in the first 100 homologation cars built.
Edgar Barth and Herbert Linge acted as chauffeurs, doing hot laps of the tree-lined circuit with members of the press – and potential customers – as passengers in one of three cars available (believed to be chassis numbers 002, 003 and 005). Of the 100 cars in the first production run, 10 were to be retained by the factory, the rest offered for sale. Within a fortnight, all but 21 had been sold. The name? Officially it was called the ʻCarrera GTSʼ – ʻ904ʼ was to remain the internal factory title, although it was soon adopted by all and sundry.
The first deliveries took place on 17 January 1964, these being two cars for Otto Zipper in Los Angeles. In all, 106 904s were listed as having been built, four of which were assembled from spare parts to satisfy demand. However, chassis numbers suggest otherwise, with a final figure of closer to 120 being likely (it is difficult to be accurate here as there is no definitive factory listing).
The 904 proved to be an incredible all-rounder, with a factory entry in the 1965 Monte Carlo Rally as proof. Driven by Eugen Böhringer and Rolf Wütherich (famous as James
“THE NAME? OFFICIALLY IT WAS CALLED THE CARRERA GTS…”
Deanʼs passenger on his fateful last journey), the tiny Porsche excelled in the snow-covered mountains, finishing an amazing second overall.
But what of the six- and eight-cylinder versions? The latter was created using the Type 771 engine from the 718 coupé. It was intended as a contender for not only class but possibly overall honours in GT races. It first appeared at the Le Mans test day in April 1964, followed by a race entry in that monthʼs Targa Florio. The 904/8 (not an official title, but one which has been adopted to differentiate between different versions of the 904) held the lead for a while until the rear suspension eventually broke. It was, however, a promising start.
Two eight-cylinder cars were appeared at the Nürburgring 1000km race in May, Edgar Barthʼs entry crashing out, while the second car – driven by Jo Bonnier and Richie Ginther – finished in fifth following problems with the throttle linkage. The same two cars were then entered for Le Mans but both were forced to retire with clutch problems – but not before being clocked at 175mph on the Mulsanne Straight!
After an unsuccessful appearance at the Reims 12-hour race in July, a single 904/8 was entered in the Paris 1000km event at the banked Montlhéry circuit outside the French capital. This car, driven by Colin Davis and Edgar Barth, finished a very creditable third overall, and second in class. Of more significance, though, was the appearance in that race of the six-cylinder 904, which was officially known as the 906 – not to be confused with the later Carrera 6, which is also widely referred to as the ʻ906ʼ – although it is often referred to unofficially as the 904/6.
This was the model the 904 was always meant to be, powered by the new Type 901 engine destined for Porsche's new road-going coupé. Two examples appeared at a test session in Monza in December 1964, one with Solex carburettors, the other with Webers. After more than 1600 miles of testing, the cars returned to the factory where various changes were made to improve airflow to the engine and transmission, amongst other things.
Just 10 904/6s were built by Porsche for the 1965 season, but plans changed somewhat when the FIA announced that for 1966, just 50 cars would need to be built to run in the new Sports Car class, allowing Porsche to consider building an entirely new car. The 904/6 was used throughout the 1965 season, the highlight of which was a fourth overall at Le Mans, winning on handicap, finishing as the top sub-2.0-litre entry and also taking honours in the Index of Performance.
The 904 will, rightfully, go down in history as quite possibly the greatest all-rounder – certainly of its time. Conceived as a Gt-class competitor, suitable for use on the road and a successful Monte Carlo Rally competitor, Butzi Porscheʼs beautiful little coupé was also the very first midengined road car sold by Porsche, and the first to use a glassfibre body. It was far more than just a pretty face in the factory line-up. CP