EF­FI­CIENCY DRIVE

When the FIA came up with new reg­u­la­tions dis­pens­ing with the old Group 5 and 6 classes, Porsche had to rise to a new chal­lenge – one that in­volved build­ing a fuel-ef­fi­cient en­durance racer. The re­sult was the mighty 956…

Classic Porsche - - Contents - Words: Keith Seume Pho­tos: Porsche Archiv and Maxted-page

Look­ing back at the story be­hind the leg­endary Porsche 956

Just when Porsche had it all sewn up, along comes a rule change that turns the race pro­gramme on its head. Such was the sit­u­a­tion in 1982 when the FIA

(Fed­er­a­tion In­ter­na­tionale de l’au­to­mo­bile) de­cided that the old Group 5 and Group 6 cham­pi­onships were due for an over­haul. Fair enough, you might say, as you need rule changes ev­ery now and then to keep things fresh. But for Porsche this was a real blow.

For sev­eral years, Porsche had dom­i­nated in­ter­na­tional en­durance rac­ing, first with the in­cred­i­bly suc­cess­ful 935 and then with the equally amaz­ing 936. Be­tween them, they crushed the op­po­si­tion in Groups 5 and 6, and peo­ple (ri­val teams, that is…) be­gan to mut­ter be­hind Stuttgart's back. These mut­ter­ings led to rum­blings, the rum­blings to a ma­jor over­haul of the reg­u­la­tions in or­der to keep en­durance rac­ing alive. No­body likes one-horse races – ex­cept, of course, the jockey on that win­ning horse…

In the 1970s, en­durance rac­ing had been dom­i­nated by Porsche and Fer­rari. The bat­tles be­tween Stuttgart and Maranello were leg­endary, but the tide grad­u­ally turned in favour of the Ger­man race team, first with the mighty 917 and then with the equally dom­i­nant 935.

The 911-de­rived sports car had shaken the rac­ing world by its foun­da­tions. Here was a car that was in­stantly recog­nis­able as a pro­duc­tion model yet wiped the floor with any­thing the op­po­si­tion could park next to it on the grid.

In 1978, Re­nault an­nounced its in­ten­tions to build an en­durance racer, con­cen­trat­ing all its ef­forts on win­ning the Le Mans 24-hour event. Which it did, con­vinc­ingly. Af­ter that, Re­nault swiftly waved bye-bye to the world of sports car rac­ing and turned all its at­ten­tion on For­mula One. The Group 6 Sports Car World Cham­pi­onship ul­ti­mately died on its feet, leav­ing the way open for Group 5 'sil­hou­ette' rac­ers to take cen­tre stage. BMW en­tered the fray with its Csl-based rac­ers, but didn't re­ally stand a chance against the might of Porsche and its 935.

So suc­cess­ful was the tur­bocharged rear-en­gined coupé that Porsche was happy to step aside in 1978, to leave the way clear

for pri­va­teers to carry the Stuttgart torch. Great for Porsche but not for the­fu­ture of ther­acese ries or, if thetruth be known, for spec­ta­tors, as vir­tu­ally ev­ery race ended up as a bat­tle be­tween pri­vately-run 935s. The gov­ern­ing body's re­sponse was to dump the old nu­mer­i­cally-ti­tled race classes in favour of three new 'Groups': A, B and – guess what? – C.

The first two re­quired cars to be built in cer­tain min­i­mum quan­ti­ties to sug­gest some form of pro­duc­tion, ef­fec­tively fill­ing thevoid left by thede mise of Group 5, while­thethird – the flag­ship class – was for pro­to­type rac­ers, gov­erned only by lim­its on di­men­sions and, con­tro­ver­sially, the quan­tity of fuel that could be con­sumed through­out a race. This was seen as an ef­fec­tive way to limit the po­ten­tial power out­put of an engine with­out re­sort­ing to re­stric­tive rul­ings on engine ca­pac­ity, valve sizes or in­take sys­tems.

There was an­other rea­son be­hind the rule change, and that was to try to re­launch en­durance rac­ing as a trans-at­lantic sport. In the USA, IMSA (In­ter­na­tional Mo­tor Sports As­so­ci­a­tion) had goneits own way, with a rule­book which was some­what at odds with the FIA equiv­a­lent in Europe. IMSA ig­nored the Euro­pean rules by plac­ing greater em­pha­sis on engine ca­pac­ity, type and man­u­fac­turer with lit­tle re­gard to tech­no­log­i­cal ad­vance­ment, al­though the ACO (Auto Club de l'ouest), or­gan­is­ers of Le Mans, had worked with the Amer­i­can or­gan­i­sa­tion to pro­motethe GTP class, which was sim­i­lar to Group 6 but more re­stric­tive. It would be some con­sid­er­able time be­fore there was any unity.

“JUST WHEN PORSCHE HAD IT ALL SEWN UP, ALONG COMES A RULE CHANGE…”

The de­ci­sion to re­strict over­all fuel con­sump­tion in Group C was made to al­low in­di­vid­ual man­u­fac­tur­ers to de­velop their own en­gines in their own way. It didn't mat­ter if you wanted to build a flat-six or a V10, fuel-in­jected or twin-tur­bocharged – what did mat­ter was that you only con­sumed fuel at a given rate. To this end, there were deemed to be three dif­fer­ent ways of polic­ing this.

First was to re­duce the ca­pac­ity of the fuel tank, at the same time lim­it­ing the flow rate of the re­fu­elling rigs. That way, if you con­sumed fuel at too high a rate, you'd lose more time sat in the pits as the tanks were filled.

Sec­ond was to place some form of flow re­stric­tor be­tween the fuel tank and the engine – much like the con­tro­ver­sial de­vice in­stalled on re­cent F1 cars. Well guess what? The idea proved to be equally con­tro­ver­sial back then, too.

The third sug­ges­tion was to im­pose a max­i­mum fuel con­sump­tion fig­ure by one of three ways: ei­ther by al­lo­cat­ing a given vol­ume of fuel for each spe­cific race, by lim­it­ing fuel tank ca­pac­ity or by re­strict­ing the to­tal num­ber of re­fu­elling stops at each event.

Each idea had its mer­its and faults. The first pro­posal was re­jected on the grounds that teams would likely de­velop ever­more pow­er­ful, less fuel-ef­fi­cient en­gines which would al­low driv­ers to drive like hell to make up for time lost in longer pit stops. Not ex­actly the most fuel-ef­fi­cient rac­ing, then. There was also the con­cern that the pits would be­come con­gested as cars would need to be re­fu­elled more of­ten.

The sec­ond idea – that of hav­ing a re­stric­tor fit­ted in the fuel line – would mean that driv­ers wouldn't have to worry about con­serv­ing fuel while they were rac­ing, and that there would be less chance of cars run­ning out of fuel on the dy­ing laps of a race. How­ever, the idea was unan­i­mously ve­toed by teams on the grounds that any such de­vice (which would pre­sum­ably be sup­plied by the race or­gan­is­ers, or at least built to their ex­act spec­i­fi­ca­tions) could prove un­re­li­able in a race sit­u­a­tion where vi­bra­tion, heat and g-forces could af­fect its ac­cu­racy.

So, be­cause it was the eas­i­est to po­lice, the third al­ter­na­tive – that of lim­it­ing fuel stops and re­strict­ing fuel tank ca­pac­ity – won the day. It was sim­ple to en­force and rel­a­tively easy for fans to un­der­stand.

The only prob­lem now was to de­ter­mine what was an ac­cept­able fuel con­sump­tion fig­ure. Paul Frère, best known in later years as a jour­nal­ist and rac­ing driver but then act­ing in his role as Vice Pres­i­dent of FIA'S Tech­ni­cal Committee, sug­gested that the Cos­worth DFV engine be used as the bench­mark.

Pro­duc­ing around 430bhp in Le Mans spec, the ven­er­a­ble Bri­tish-built V8 con­sumed fuel at around 30–35 litres/100km (that's roughly 8 or 9mpg). 'No way!', said the man­u­fac­tur­ers, who pushed for a min­i­mum fig­ure of 60 litres/100km – that's just 4.7mpg…

“THERE COULD BE NO MOV­ABLE AERO­DY­NAMIC DE­VICES”

Thanks no doubt to the (for once) united front shown by the race teams, they got their way and the first 'fuel-ef­fi­cient' en­durance race se­ries saw com­pet­ing cars con­sum­ing fuel at a rate that would make an oil sheik smile.

But the re­quire­ment to abide by a min­i­mum fuel con­sump­tion rul­ing wasn't the only fly in the oint­ment. Just about ev­ery as­pect of the Group C reg­u­la­tions dif­fered from those of the out­go­ing Group 5 and 6 classes. Let's take a look at what Porsche (and its ri­vals, of course) had to con­tend with.

Firstly, as far as the body­work was con­cerned, there were strict lim­i­ta­tions on what we re­fer to to­day as the aero pack­age. There could be no F1-style side-skirts (re­mem­ber them?), and wheels had to not only be cov­ered for at least a third of their cir­cum­fer­ence, but across their whole width. There could be no mov­able aero­dy­namic de­vices.

The reg­u­la­tions in re­spect of the aero­dy­nam­ics ex­tended as far as the un­der­side of the car, too. There had to be a flat sur­face, mea­sur­ing 1000mm x 800mm be­tween the rear of the front wheels and the front of the rear wheels. Oh, and no other part of the body­work could ex­tend be­low the level of this flat belly-plate, mean­ing there could be no 100 per cent de­pen­dence on ground-ef­fects tun­nels to keep cars firmly glued to the road.

There were also lim­its on the over­all size – no car could be greater than 4.8 me­tres in length, and 2.0 me­tres wide, while the to­tal front and rear over­hangs could not mea­sure more than 80 per cent of the wheel­base. There was also a min­i­mum weight. This was set at 800kg for the first two sea­sons (1982–83), in­creas­ing to 850kg in 1984 when Imsa-spec­i­fi­ca­tion cars were al­lowed to com­pete.

As for the engine, that was to all in­tents and pur­poses 'free' – the only re­stric­tion was that it had to be man­u­fac­tured by a com­pany which had cars ho­molo­gated in Groups A (pro­duc­tion cars) or B (grand tour­ing cars). The for­mer re­quired the man­u­fac­turer to build a min­i­mum of 5000 ex­am­ples in a 12 month pe­riod, the lat­ter just 200.

But it was the fuel sys­tem that came in for some of the most de­tailed reg­u­la­tion, as one might ex­pect. The fuel tank – a flex­i­ble 'bag' tank for safety rea­sons – could have a ca­pac­ity of no more than 99 litres, while fuel lines (which should have an out­side diameter of no more than 20mm) were deemed to hold just one litre of fuel, mak­ing a to­tal of 100 litres of fuel on board at any one time.

As far as re­fu­elling was con­cerned, each car could only be filled us­ing a grav­ity-fed rig with a max­i­mum flow of 50 litres/minute, mean­ing each re­fill at a pit stop would take less than two min­utes – as­sum­ing the car hadn't run out of fuel in the mean­time, of course.

The num­ber of re­fu­elling stops per event was limited ac­cord­ing to the length or du­ra­tion of the race. For an 800km race, teams could stop four times, for 100km and six hour races, this rose to five stops, while 12 hour en­durance events al­lowed the cars to make 12 stops, and 24 hour races 25 stops.

When Peter Schutz was ap­pointed CEO of Porsche in 1981, he took an ac­tive in­ter­est in Porsche's mo­tor­sport in­volve­ment. The com­pany had an il­lus­tri­ous his­tory in en­durance rac­ing, start­ing with class wins at Le Mans as far back as the early 1950s, reach­ing a high in 1970 with its first out­right win with Attwood and Her­rmann in the 917. From there, the torch was car­ried by the 935, fol­lowed by the 936. There was, of course, the 924GTR pro­gramme, but at best that would only of­fer Porsche the chance to gain a class win. Schutz wanted more than that: he wanted over­all vic­tory.

With that in mind, he gave his bless­ing to the de­vel­op­ment of a new car de­signed to meet the forth­com­ing Group C reg­u­la­tions. He also made what was to prove one of the most far-reach­ing de­ci­sions of his ten­ure, and that was to sep­a­rate the race and pro­duc­tion fa­cil­i­ties, mov­ing the for­mer to Weis­sach, while the lat­ter re­mained at Zuf­fen­hausen. In charge of the new race depart­ment was Peter Falk, who had been with Porsche for over 20 years.

The 956 may have come un­der Falk's ju­ris­dic­tion but it was Nor­bert Singer who mas­ter­minded the project. Singer had been with Porsche since 1970, join­ing at a time when the 917 was king, and rel­ished the op­por­tu­nity to over­see the de­sign of a new car from scratch.

The task of de­sign­ing a chas­sis to fit the new reg­u­la­tions was handed to Horst Reiter, while the body­work and aero­dy­namic pack­age was looked af­ter by Singer, along with Eu­gen Kolb. As for the engine, that was the charge of Valentin Scha­ef­fer, with Klaus Bischoff and Wal­ter Na­her ap­pointed race en­gi­neers.

The pro­gramme of­fi­cially came into be­ing on 20 July 1981, even though the reg­u­la­tions for Group C had still to be fi­nalised. This left barely 10 months to de­sign, build and test the 956 ahead of the Le Mans test day, fol­lowed by the race it­self in June 1982.

It was an ambitious project with a des­per­ately tight sched­ule, but when Ferry Porsche was pre­sented with a 1/5th-scale model, there was no turn­ing back…

The 956 was a com­plete de­par­ture from nor­mal Porsche prac­tice, with Horst Reiter turn­ing his back on the pre­vi­ous­ly­favoured tubu­lar chas­sis con­struc­tion in favour of an all-new mono­coque de­sign – a first for Porsche. This method of con­struc­tion gave en­gi­neers a far greater op­por­tu­nity to ex­ploit ground-ef­fects, with tun­nels chan­nelling air un­der the car. With a tubu­lar chas­sis, this was vir­tu­ally im­pos­si­ble. An­other ben­e­fit of mono­coque de­sign was that the chas­sis was far stronger, of­fer­ing con­sid­er­ably im­proved driver pro­tec­tion in the event of an ac­ci­dent.

The cho­sen ma­te­rial was alu­minium sheet, which was then folded, bonded and riv­eted to­gether. True, that by 1981, the For­mula One in­dus­try was al­ready us­ing car­bon-fi­bre as the pre­ferred ma­te­rial with which to con­struct a chas­sis, but Reiter was as yet un­con­vinced of its abil­ity to with­stand the stresses and strains of long-dis­tance en­durance rac­ing. Porsche did not wish to take any risks that might jeop­ar­dise its chances of over­all vic­tory at La Sarthe. And of course, alu­minium struc­tures

could also be re­paired at the track, fol­low­ing an 'off'…

By to­day's stan­dards, the un­der­stand­ing of aero­dy­nam­ics in 1981 was at a rel­a­tively early stage. Wind-tun­nels were in com­mon use, but there were none of the so­phis­ti­cated com­puter-con­trolled mov­ing-road tun­nels that are so fa­mil­iar to­day. But that did not mean Nor­bert Singer and Eu­gen Kolb were un­able to work magic with the 956.

The prob­lem Porsche now faced was that the large flat sur­face be­neath the cock­pit dic­tated by the rule book meant that there could be no ful­l­length ground-ef­fects tun­nels un­der the car.

In­stead, the two de­sign­ers came up with an in­ge­nious solution that al­lowed air to en­ter the un­der­side of the car from two ar­eas: 50 per cent un­der the nose, 50 per cent un­der the side pan­els. The air was then chan­nelled into two tun­nels at the rear of the car, one each side of the gear­box, leav­ing only the drive­shafts and sus­pen­sion arms ob­struct­ing the flow. To fur­ther fine-tune the de­sign, the engine and trans­mis­sion were tilted up by a few de­grees to al­low the shape of the tun­nels to be op­ti­mised.

Pow­er­ing the oth­er­wise all-new car was a tried and tested engine – the fac­tory des­ig­na­tion '935/76' hinted at its ori­gins. This was es­sen­tially the same twin-tur­bocharged unit that had proved so suc­cess­ful in the 936, with its roots dat­ing back five years to the 935. It was eco­nom­i­cal by race engine stan­dards, con­sum­ing fuel at less than 52 litres/100kms (or roughly 5.4mpg), so well within the lim­its dic­tated by the FIA'S new Group C reg­u­la­tions.

With wa­ter-cooled cylin­der heads yet with cylin­ders still cooled by air, it had proved to be in­cred­i­bly re­li­able, and with boost set at a rel­a­tively mod­est 1.1 bar (just un­der 16psi), the 2649cc six-cylin­der engine pro­duced 620bhp. It was used in con­junc­tion with a five-speed trans­mis­sion.

The 956 was first tested at Weis­sach in March 1982, where chas­sis num­ber 956.001, the de­vel­op­ment car, ap­peared in rather un­der­stated white, grey and beige body­work. Driven by Jür­gen Barth, it showed con­sid­er­able prom­ise right from the off. More test­ing took place at Paul Ri­card later that same month, this time at the hands of Jacky Ickx and Jochen Mass, fol­lowed by an­other ses­sion in May where the two were joined by Derek Bell. To­gether, the trio put in nu­mer­ous laps, part of the aim be­ing to get used to the han­dling with the ground­ef­fects chas­sis. That the car 'worked' was clear for all to see – it was to prove some 10Km/h faster than the 936.

The first com­pet­i­tive out­ing was at Sil­ver­stone in May 1982, where '001', driven by Jacky Ickx and Derek Bell and sport­ing its new Roth­mans liv­ery, fin­ished sec­ond over­all, and first in class.

“956S NOTCHED UP FOUR CON­SEC­U­TIVE VIC­TO­RIES…”

It might have won, too, but no­body had ex­plained to the driv­ers the full im­pli­ca­tions of rac­ing with fuel econ­omy in mind. Go­ing all out in qual­i­fy­ing, Ickx put 956.001 firmly on pole but Peter Falk had to ex­plain if they drove like that in the race, they would run out of fuel…

Re­leased for the 1984 season, the 956B was the ul­ti­mate de­vel­op­ment of the 956, de­signed and built to the 1983 works Roth­mans spec­i­fi­ca­tion, fea­tur­ing Motronic fuel in­jec­tion, mod­i­fied sus­pen­sion and a one-piece un­der­body. The Motronic fully elec­tronic and in­te­grated ig­ni­tion and in­jec­tion sys­tem made much closer con­trol of the com­bus­tion process pos­si­ble, pro­vid­ing more power, bet­ter fuel con­sump­tion and a more pro­gres­sive throt­tle re­sponse.

Com­bined with Nor­bert Singer's aero de­vel­op­ment to the un­der­body, the 956B was the ul­ti­mate spec­i­fi­ca­tion of the 956. Just four 956Bs were orig­i­nally built for the lead­ing 1984 World Cham­pi­onship pri­va­teer teams – one of which is the dou­ble Le Mans win­ning Joest-newman car (956.117) and to­day just three of these cars still sur­vive, af­ter Ste­fan Bellof's fa­tal ac­ci­dent in chas­sis #956.116.

While the 917 may be the most iconic Porsche Pro­to­type de­sign, the 956/962 Group C cars were by far the most suc­cess­ful Porsche Pro­to­type rac­ing cars built so far. Over the next four years, 956s notched up no fewer than four con­sec­u­tive vic­to­ries at Le Mans and proved to­tally dom­i­nant in all av­enues of in­ter­na­tional sports car rac­ing. It proved yet again that if Porsche sets its mind on win­ning, few others stand a chance. CP

Above: An early photo of #001 be­ing read­ied for wind tun­nel test­ing at Weis­sach. Bare glass­fi­bre mould­ings lacked de­tails such as head­lights at this stage

Be­low left: Taped up ready for fur­ther wind-tun­nel tests, #001 would never have won any beauty con­tests!

Be­low right: Like most en­durance rac­ers, the Porsche 956 was built with right-hand drive – but few crea­ture com­forts…

Be­low: Even at pro­to­type stage, spon­sors’ lo­gos still fea­tured – but then, with­out their fi­nan­cial­sup­port, the race pro­gramme prob­a­bly wouldn’t have gone ahead. Bat­tle scars on the body­work of 956.001 were tes­ti­mony to a hard life on the Weis­sach test tra

Above left: Ev­ery­thing about the 956 was new, ex­cept for the engine, which was the tried and tested 935/76 unit as used in the out­go­ing 936 race cars. In­board sus­pen­sion aided air­flow un­der the rear of the chas­sis

Above right: Pro­to­types led a hard life – ‘racer tape’ was very much in ev­i­dence…

Be­low: Dom­i­na­tion! Le Mans 1982 and Porsche956s cross the­linein first, sec­ond and third po­si­tions. The win­ning car (aptly car­ry­ing the num­ber ‘1’) was driven by Jacky Ickx and Derek Bell

Above left: With Jür­gen Barth at the wheel, the first 956 takes to the Weis­sach cir­cuit. In thep­hoto you can clearly see the ground­ef­fects tun­nels at the rear

Above right: Jür­gen Barth had car­ried out the first ex­ploratory drives of ‘001’, be­fore hand­ing over to Ickx, Mass and Bell for fi­nal pre­race test­ing in March 1982

Be­low: 956.115 is one of just four ‘956Bs’ ini­tially built for the 1984 WSC pri­va­teer teams. Just three of these sur­vive, as #116 was de­stroyed in Ste­fan Bellof’s fa­tal ac­ci­dent at Spa in 1985

Above left: A 956 was used to test the V6 turbo TAG engine des­tined for use in Porsche’s Indy Car pro­gramme Above right: Sil­ver­stone SixHour May 1982 saw Porsche 956.001 fin­ish sec­ond over­all, driven by Jacky Ickx and Derek Bell

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