PORSCHES UNDER PRESSURE
Classic Porsche recounts the story behind Porsche’s legendary Turbos
T urbo – the very word conjures up an image of power, be it in the form of Porscheʼs musclebound, wide-arched 930 coupé or the mighty 917 Can-am racers driven to victory by the likes of Mark Donohue and George Fullmer. Today it seems just about every other car on the road is turbocharged, be it a tiny Tdi-badged hatchback or a Tarmacshredding supercar. But it hasnʼt always been that way.
Turbocharging as a way to extract power from an internal combustion engine has been with us since 1905, believe it or not, when Swiss engineer Alfred Büchi took out a patent for an exhaust-driven supercharger. Ten years later, a turbocharged Liberty aero engine was dynoʼd at 360bhp, compared to just 220bhp of its normally-aspirated counterpart. Pretty soon, turbocharged engines became widely accepted in aviation circles.
However, it wasnʼt until 1962 that the first production car powered by a turbocharged engine was launched: the 215bhp Oldsmobile Jetfire. This was followed soon after by Chevroletʼs 152bhp Corvair Monza, launched in 1962 and still in production in 1966 as the 182bhp Monza Corsa. But widespread acceptance of the technology in racing circles would take a little longer.
The first appearance in Can-am of a turbocharged car was at St Jovite in 1969, when Joe Leonard finished eighth in the wedge-like Mckee, using a twin-turbocharged 389ci (6375cc) iron-block Oldsmobile engine. This gave his team the confidence to develop the concept further, entering two new cars at Elkhart Lake. These amazing machines also featured a chassis from Mckee, with new 455ci (7456cc) allaluminium engines, two-speed automatic gearboxes (with hiand low ratios, to give four speeds) – and four-wheel-drive. Sadly, the cars were plagued with brake problems and never turned a wheel in anger, a lack of finances bringing the project to a premature end. But the die had been cast: turbocharging had left its indelible mark on Can-am, a point that had not been lost on Porscheʼs engineers.
Porsche had what appeared to be the perfect engine available in the form of the Type 912 (definitely not to be confused with Porscheʼs four-cylinder coupé…), a 630bhp 5.0-litre flat-twelve developed for the 917 endurance racers. You could be forgiven for thinking that 630bhp in a car weighing just 1638lbs would be enough to force the opposition to eat Porscheʼs dust, but arch-rival Mclaren boasted in excess of 700bhp from its fuel-injected Chevrolet engines, and considerably less weight. Porsche needed to go one better.
There were two options available, the first being to increase the capacity of the motor, but the Type 912 engine had almost reached its limits – the 86.8mm Nikasil-coated cylinders were already tight up against each other, leaving little scope for increasing the bore. Using 90mm pistons and cylinders, the capacity could be increased to 5374cc, which saw the power output rise to 660bhp – better but still not enough to trounce the Mclarens.
Porsche also investigated the concept of stretching the 12-cylinder Type 912 motor even further by adding four more cylinders – in fact, they built 10 flat-16 prototype motors, ranging in size from 6.0- to a whopping 7.2-litres. The latter produced some 880bhp on the dyno, theoretically more than enough to dispense with anything Mclaren had to offer. But it was a big engine – very big – and Penske-porsche driver Mark Donohue quipped that you could hear one end of the engine start before the other. However promising the flat16 may have looked, its development was terminated in favour of option two…
It was clear that turbocharging was an obvious way to make significant power increases, but what made turbocharging particularly attractive in Can-am racing was
that, unlike in virtually every other race series, there was no penalty for running a turbo- or supercharged engine. This lax ruling gave engineers carte blanche to explore the very limits of turbo technology – and explore it they did. In 1971 Porsche built a car that would turn Can-am on its head: the 917/10 with a turbocharged Type 912 flat-12 engine, to be used in an all-aluminium space-frame chassis.
The 917/10 featured dual turbochargers, one for each bank of cylinders, supplied by the German company Eberspächer, a name more familiar today with petrol heaters used in campers and commercial vehicles. Eberspächer worked closely with the Us-based Airesearch operation, which had considerable experience with race car installations through its involvement with the USAC series.
Itʼs Hans Mezger that we can thank for steering Porsche down the turbocharging route. He saw the potential benefits of forced induction and encouraged one of his team, Valentin Schäffer, to look into turbocharging a 4.5-litre version of the Type 912 engine. Schäffer ʼs solution was straightforward: you have two banks of cylinders, you use two turbos – just like on the Mckee-oldsmobile Can-am engine. To limit maximum boost, and therefore prevent the engine from overboosting and destroying itself, a single wastegate was fitted.
Early tests with the dual-blown Type 912 motor in the 917/10 chassis were ʻinterestingʼ. Jo Siffert was the test pilot and he found this first taste of turbocharging unpredictable to say the least. The turbos seemingly took an age to ʻspool upʼ, to use modern parlance, and equally as long to bleed off boost. The result was that as Siffert applied throttle exiting a corner, there was a sizeable delay before anything happened – and when the motor did come on boost, it happened very quickly. Conversely, when he lifted off the throttle at the end of the straight, the turbos continued to spin at speed, producing boost when it wasnʼt needed. As a consequence of this, itʼs said that Siffert visited the vegetation alongside the Weissach test facility on more than one occasion.
Can-am regulations, as mentioned, were lax and placed no restrictions on engine capacity, nor did they factor in a special index for turbos. However, Porsche was not a company renowned for ʻgoing for brokeʼ so limited its Type 912 engine to just 1.5 bar (22psi) – still enough for 1000bhp at 7800rpm, and a massive 725lb ft of torque at 6400rpm.
For ʻnormalʼ use, Porsche restricted boost to 1.3bar (18psi), which limited output to just under 900bhp – still almost 200bhp more than the Mclarens.
In an effort to combat the effects of turbo lag, and overboost on a trailing throttle, Porsche had developed a system of air valves, some of which bled off manifold pressure when the throttle was closed, while others opened to the atmosphere when the throttle was applied at low rpm – effectively turning the car into a normally-aspirated configuration until the engine produced positive boost. The result was a car that could accelerate from 0–60mph in 2.1 seconds, 0–100mph in 3.9 seconds and 0–200mph in just 13.4 seconds!
No wonder people were sitting up and taking notice when the Penske-porsches came to the line in 1972. However, star driver Mark Donohue was injured in a crash at Road Atlanta, meaning that he was unable to capitalise on his development experience, George Follmer being brought in to take his place for much of 1972, ending the year as champion.
The 917/10 was clearly a massive force to be reckoned with, but Porsche had more up its sleeve for 1973. The 917/10ʼs chassis was cut in two and experiments carried out with different extensions to alter the wheelbase. Eventually Mark Donohue felt happiest with a wheelbase of 2500mm (98.4in), which had the added benefit of allowing a larger fuel tank to be used, increasing fuel capacity from 86 gallons to a whopping 106 gallons.
Further research was carried out on aerodynamics, Porsche calling on the services of French aeronautical company, SERA. The result was a new body with a redesigned nose, which came to be referred to as the ʻParis bodyʼ. The result was a 212mph speed recorded at Paul Ricard in France. Power was up for 1973, too, the 5.4-litre engine (Type 912/52) now producing 1100bhp, with 1500+ seen on the dyno. The driver now had control of boost, too, with a large knurled knob in the cockpit allowing Donohue to to adjust the wastegate settings at will. With rivals falling by the wayside, Porsche – and Donohue – walked away with the Can-am championship…
Porscheʼs domination of Can-am was ultimately responsible for the seriesʼ demise. The organisers, SCCA, went against their agreement not to alter rules with less than
“PEOPLE WERE SITTING UP AND TAKING NOTICE…”
a year ʼs notice and talked of limiting engines to match those used in F5000 single-seaters. That meant a limit of 3.0-litres for cars with ʻrace enginesʼ (ie, non-production-based, multicam designs) or 5.0-litres for those with ʻiron-blockʼ production-based motors. Front-runners in Can-am, PenskePorsche and Shadow, both expressed their dislike and Porsche allowed Penske to opt out of its three-year contract a year early. Can-am struggled on for one more year before SCCA pulled the plug on November 19th 1974. But the experience gained would not go to waste.
As far back as 1969, Porsche had looked into turbocharging its flat-six engine, with experimental work being carried out on a 2.0-litre 911. However, although the engine ran, it was never installed in a car (one can only imagine the results had this line of development been pursued so long ago…). The concept of turbocharging a road car was resurrected in 1972, almost certainly kicked into life, not only by the news that BMW was about to launch its 2002 Turbo, but also that Porscheʼs Bavarian rivals had displayed an exotic gull-winged sports car powered by a turbocharged engine, which threatened to encroach on ʻtheir ʼ territory.
Porscheʼs own experiments in 1972 were based around a 2.7-litre engine, that featured an induction system not dissimilar to that of the contemporary Can-am motors. Dynamometer tests held early in 1973 suggested that reliability wouldnʼt be an issue, so the go-ahead was given to take the project to the next stage by installing a version of the engine in a road car. Initial tests at Weissach showed up two problems, neither of which was insurmountable: the chassis required further development to handle the extra horsepower, and the engine suffered from unacceptable levels of turbo lag. But power – of that there was plenty, with around 250bhp on tap.
Company chairman Ernst Fuhrmann was impressed with the initial results but, in an effort to keep costs down, insisted that any further development work revolve around the use of the new K-jetronic fuel-injection system. With a single turbocharger located low-down to the left rear of the engine, close to the exhaust pipework and helping to keep the centre of gravity as low as possible, the prototype 911 turbo engine was one step nearer to being production-ready.
The task of taking things to the next level was entrusted to Herbert Ampferer, who in 1985 would go on to file a patent for Porscheʼs Varioram induction system. The biggest
problems Ampferer faced were finding a cure for the one-off switch-like nature of these early turbo installations and packaging the whole system in a way that made it suitable for production. But by summer 1973, Porsche felt it was ready to tell the world the news: a turbocharged 911 was on the horizon.
Type 930, as the new project was to be called, first saw the light of day at the 1973 Frankfurt motor show. On display was a 911 the likes of which had not been seen before, with wider front and rear wings, stretched to cover deep 15indiameter wheels, a front air dam and a large ʻwhale-tailʼ rear spoiler. The bodywork was effectively that of the 3.0-litre RS and IROC cars, finished in a pearlescent silver. Bold ʻPorscheʼ graphics in white along each flank left nobody in any doubt as to who had built the car, but even bolder ʻTurboʼ lettering over each rear wing made it clear this was no ordinary Porsche… A quick glimpse inside reinforced this as the car featured a pair of Recaro ʻlollipopʼ seats, trimmed in plaid, with full harness seat belts for driver and passenger.
Curious visitors to the show stand enquired what lay under the rear lid. The answer was not always the same – some people appear to have been told it was a 2.1-litre turbocharged engine producing 280bhp (presumably of the type that would appear in the forthcoming RSR Turbo) but most were informed it was a 2.7-litre engine capable of propelling the car to a top speed of over 160mph. What nobody was told, though, was that the engine was a mockup, with a dummy induction system, incapable of running before, during or after the show.
The Frankfurt show car served as something of a watershed within Porsche, leading to two separate lines of development: one as a limited-production road car (Type 930), the other as a full-blown competition car (RSR Turbo). From this point on, the teams responsible concentrated on their own individual projects – both would prove to be ultimately successful in their endeavours.
Thereʼs little doubt the display car captured everyoneʼs imagination, but Porsche couldnʼt promise it would be a full production model. Indeed, the initial plans were that it would serve as a way for the company to go racing in Group 4 GT competition, where there was a requirement to build a minimum of 400 examples. Once those relatively few cars had been built and sold, that was it – the 911 Turbo would have served its purpose.
But even the task of selling 400 of these cars didnʼt promise to be easy, for as 1973 drew to a close, so OPEC implemented a boycott of oil supplies, which turned the automotive world on its head. Without oil, there could be no petrol. Without petrol, what market would there be for a highpowered turbocharged sports car? It seemed as if the Type 930 was destined to be still-born. Even BMW had killed off its wonderful 2002 Turbo…
But Fuhrmann had other ideas. He was determined to see things through, despite on-road testing being curtailed due to the ban on Sunday driving imposed in Germany, along with speed restrictions on the autobahns and, incredibly, tracks such as the Nürburgring, Hockenheim and even Porscheʼs own Weissach facility. The restrictions were gradually eased, allowing Porsche to flex the Turboʼs legs more often. But the matter remained of how to sell the concept to a market still reeling from the effects of OPECʼS stranglehold on oil supply.
The debate centred round pricing. There were two schools of thought, one being that the 911 Turbo should be sold as a stripped-down model at a rock-bottom price. Although this may seem a strange idea now, bear in mind that a) there were people prophesying the end of performance cars as we know them due to fuel shortages and b) it would be a quick way to get rid of 400 cars so that the factory could homologate the Grp 4 entries.
On the other side of the fence were those – Fuhrmann among them – who felt that the car deserved to be sold as a luxury item, a well-equipped range-topping model with a price tag that matched its obvious quality. Ultimately this was the winning argument and the decision was made to market the 930 accordingly. One year later, at the 1974 Paris Salon dʼauto, the production version of the 911 Turbo was shown for the first time – a well-equipped, highly-specʼd Porsche that marked the companyʼs first venture into the world of road-going supercars.
Jürgen Barth recalls that, while working with the press department in 1976, he was tasked with driving the 911 Turboʼs first 400 customers to give them instruction on how to handle this powerful new model. ʻI drove each of them from the factory on a high-speed run up to Heilbronn, taking the opportunity to explain the car in detail to the new owners. This was a special service I was asked to do by the sales department.ʼ
Looking back, itʼs perhaps difficult to appreciate what a monumental impact the 911 Turbo had on those involved with Porsche in the 1970s. It was in a league of its own and proved once and for all that, on track or on the street, Porsche could run with the big boys. CP