Guide: Porsche 935/78
Background
By the late 1970s, Porsche had become the pre-eminent force in Sports and GT racing.
The Stuttgart firm had returned to front-line competition in 1976, since which time the 936, 935 and 934 had dominated Group 6, Group 5 and Group 4 respectively.
Crack works cars in the top two categories had been supported by an army of slick privateers armed with 935s and 934s; a combination of prodigious speed, strength in depth and superior reliability meant other manufacturers rarely got a look in.
Porsche had first begun racing the 935 in 1976 when it was reserved for works use.
In 1977, the factory team moved up to a new twin turbocharged 935, at which point single turbo 935s were offered to customers.
For 1978, the factory decided to run a drastically reduced campaign and let their customers have a crack at the World Championship. A further uprated 935 was once again developed, but the intention was to go for victory at Le Mans which was not a round of the World Championship (as had been the case since 1975).
This latest 935 (the 935 / 78) was easily the most extreme yet.
Thanks to canny interpretation of the rules it became longer, lower and wider than before. Slung out back was the most radical Porsche engine since the dual overhead camshaft Carrera unit of the 1950s. Power-wise it was the most potent since the epic Group 7 917/30 of 1973.
In 1976, Porsche had pushed the Group 5 regulations to the limit with the 935’s famous Flachbau front end and an air-to-air intercooler (the latter of which was ultimately deemed illegal).
For 1977, the 935’s bulkheads had been repositioned. However, the 935 / 77 arrived too late to take advantage of a new ruling created to try and help BMW and Ford who were using front-engined designs.
Towards the end of 1976, the FIA had added a loosely worded supplement that concerned rocker panel height; they would now allow manufacturers to modify the sills so that exhausts did not have to run underneath the floor. This would enable the floor and consequently the ride height to be substantially lowered.
Even though Porsche’s rear-engined layout was not affected by the ruling (the 935’s exhausts exited at the back of the car), the Weissach racing department decided to fully exploit the new rule and build a car with a much lower floor / ride height for 1978. The 935 / 78 was in fact so low that the gearbox had to be inverted to ensure the driveshafts were not inclined at an impossible angle.
And Porsche did not stop there.
Another ruse concerned interpretation of the Body Structure which the FIA categorised as the area between the front and rear bulkheads. As the zones outside these areas were open, Porsche decided to replace the existing structure with light alloy spaceframes.
To these, massively extended front and rear body sections were fitted and the doors became fully shrouded with a second skin to conform with the dramatically widened fenders.
Chassis
In terms of the original 911’s steel monocoque, only the roof section from the A pillar back to the B pillar was actually retained. The rest of the assembly was pure spaceframe with additional subframes riveted in place to support the bodywork and running gear.
The new floor was fabricated from aluminium with glassfibre sandwiched in between. It replaced the original steel floor (which had been removed at sill level) and resulted in a 60mm lower ride height.
Porsche claimed the new chassis to be 40% stiffer than before.
The suspension was also heavily revised; double wishbones with MacPheson struts were now fitted up front while the back end used aluminium semi-trailing arms. Progressive-rate coil springs were fitted all round along with gas-filled Bilstein dampers and an adjustable anti-roll bar at either end.
The uprated brake system comprised cross-drilled and ventilated 332mm discs with monobloc four-piston calipers.
Massive new centre-lock wheels (16 x 11-inches at the front and 19 x 15-inches at the rear) were shod with specially developed Dunlop Racing tyres.
A 120-litre fuel tank was located ahead of the front bulkhead.
Engine / Gearbox
The Type 935/71 engine used for 1978 was another dry-sumped twin turbocharged all-alloy Flat 6.
Although the rules stated that Porsche had to retain the usual air-cooled production block (with just some machining permitted), the cylinder heads were open for modification.
With this in mind, the original air-cooled SOHC two valve heads were replaced with new water-cooled DOHC four valve units from the latest 936.
Each bank of cylinders had its own water pump which lowered the temperature of the heads significantly.
As only the block had to be air-cooled, Porsche were able to run the 937/71 engine with a smaller fan.
It was also decided to substantially increase displacement. Bore dimensions were taken out from 92mm to 95.7mm and the stroke was extended from 70.4mm to 74mm. The engine size went from 2857cc to 3211cc which represented a gain of some 354cc.
This gave a swept volume of 4498cc when the multiplier for turbocharged engines was taken into account. It meant the 935 / 78 was placed into the over four-litre category where a 1025kg minimum weight limit was enforced.
Compression was set at 7.0:1 and Bosch mechanical fuel-injection was employed.
With a pair of KKK K29 turbochargers running at 1.5 bar, peak output was 750bhp at 8200rpm.
If the turbos were cranked to 1.7 bar, as much as 845bhp at 9000rpm was possible.
The inverted Type 930/50 gearbox was a four-speed unit. Porsche fitted a 240mm Fichtel & Sachs clutch along with titanium driveshafts from the 917.
Bodywork
If the 935 / 78’s mechanical specification was not extraordinary enough, a series of radical cosmetic enhancements really took the breath away.
All new front and rear body sections were permitted because the Group 5 rules stated only what was between the front and rear bulkheads had to retain the production car silhouette.
This meant only the roofline retained any 911 Turbo DNA and the rest of the car was akin to a purebred Prototype.
Everything bar the roof was fashioned from ultra lightweight fibreglass.
Vents and ducts were carved out from every panel to feed the myriad radiators that were scattered around the car.
At the back was an enormous rear spoiler mounted on twin pylons.
Fared-in doors each housed an enormous NACA duct.
Overall, the 935 / 78 had an aerodynamic value about on a par with the slippery 917 Langheck of 1971.
Interior
Unlike previous iterations of the 935, this latest variant was built in right-hand drive for optimal weight distribution on clockwise circuits.
The 911’s standard five-gauge dash was retained, albeit untrimmed in bare metal. Another five gauges were located on a vertical control panel ahead of which was an exposed gear shift mechanism and adjustable boost pressure dial.
Porsche also fitted a single bucket seat and intercom system.
Weight / Performance
Because the 935 / 78 tipped the scales at 960kg, 65kg of lead ballast was added in the passenger footwell to get to the 1025kg class minimum.
0-62mph required just 2.6 seconds and top speed was 227mph.
Initial FIA Approval
As the FIA operated a system where new cars could be inspected at the design stage, Porsche requested a visit from one of the governing body’s representatives to assess what they knew would be a controversial machine.
FIA delegates Paul Frere and Curt Schild called on the factory in February 1978. They went over the design in detail and confirmed that it complied with the regulations.
Completion
The finished 935 / 78 was given a shakedown test at the Weissach proving ground by Jurgen Barth in the first week of March. Without its colourful Martini stripe kit, the vast machine soon acquired the nickname Moby Dick in reference to the mythical white whale.
Porsche then headed to Paul Ricard during the second week of March. Here, the 935 / 78 was evaluated with nine new tyre compounds and five different constructions. Lap times were three seconds faster than the 935’s previous best time.
By this stage, Porsche had just the one complete car (chassis 006) with a spare (007, a bare tub with front and rear subframes) waiting in the wings should it be required.
1978 Season
Porsche’s 1978 campaign would revolve around the Le Mans 24 Hours which took place over the weekend of June 10th and 11th. They would run four Martini-backed cars at la Sarthe: a trio of Group 6 936 Prototypes and the solitary 935 / 78 in Group 5.
Prior to Le Mans, the 935 would be given an outing at the Silverstone 6 Hours on May 14th; the British track’s fast and flat layout was traditionally seen as an ideal warm up ahead of Le Mans.
Only production-based cars from Groups 1 to 5 were permitted to compete in the World Championship. Le Mans was not part of this which meant it was the only major race that allowed Group 6 Prototypes to run. In 1976 and 1977, a separate World Championships had been organised for Group 6 cars, but this had been abandoned for the 1978 season.
FIA Reversal
Unfortunately, at an FIA technical commission meeting in Lisbon three weeks before the race at Silverstone, the FIA reversed their decision to approve the 935 / 78.
The problem concerned its fared-in doors which were declared illegal.
As a consequence, Porsche were forced into a late redesign; the doors became semi-shrouded with covers at either end and an exposed central section.
1978 Silverstone 6 Hours
The revamped machine made its debut at Silverstone in mid May (round four of the World Sportscar Championship). In addition to the reconfigured doors, chassis 006 also arrived sporting a new rear spoiler.
Jochen Mass and Jacky Ickx were brought in to drive, however, Ickx’s flight from Belgium was delayed which meant he missed practice and the Saturday morning qualifying session.
On a damp track, Mass ran the turbos at just 1.45 bar, but still managed to smash his lap record from 1977 by over four seconds.
During the dry afternoon session, Ickx lopped off another seven tenths to secure pole position by a comfortable 1.5 seconds from the Georg Loos 935 driven by John Fitzpatrick and Toine Hezemans. The Kremer 935 of Wollek / Pescarolo was third followed by Georg Loos other two 935s. The solitary works BMW 320i Turbo driven by Ronnie Peterson and Hans-Joachim Stuck lined up sixth.
The race got underway in light rain.
Mass accelerated clear of Hezemans and, by the end of lap one, had established a 4.3 second lead.
With six laps gone, the gap had risen to 18 seconds and Mass was already well into the backmarkers.
Conditions then dried up and, wanting to re-emerge in the lead, Mass was the last of the front runners to stop.
At the one hour mark, Mass had lapped the entire field to include the second place Wollek / Pescarolo entry.
With two hours gone, the works car had established a two lap lead over Hezemans / Fitzpatrick.
It then began to drizzle again, at which point Mass came in to hand over to Ickx.
By mid-distance, Ickx held a three lap lead over the Peterson / Stuck BMW (which had risen to second but retired soon after).
The 935 / 78 had a four lap lead at the four hour mark with Wollek / Pescarolo now back in second for Kremer.
This advantage had grown to six laps by the five hour mark, at which point the car was brought in for a fresh set of brake pads.
Ickx and Mass ultimately finished an amazing seven laps clear of the chasing pack. Wollek / Pescarolo claimed the runner up spot while third went to the BMW Belgium 320i of Harald Grohs / Eddy Joosen who finished nine laps adrift of the second-placed Kremer 935.
1978 Le Mans 24 Hours
After an astonishingly dominant display at Silverstone, Porsche headed to Le Mans four weeks later thinking the 935 / 78 might be in with a shout of an outright victory even though a smaller fuel tank meant it would have to stop more frequently than the Group 6 entries (every 45 minutes as opposed to every 80).
Rolf Stommelen and Manfred Schurti were down to drive chassis 006 while the trio of 936s were allocated to Jacky Ickx / Henri Pescarolo, Bob Wollek / Jurgen Barth and Hurley Haywood / Peter Gregg / Reinhold Joest (the latter with a single instead of twin turbo example).
Although the 935 / 78 proved faster through the Mulsanne Straight speed trap (227mph compared to 216mph), it was the 936 of Ickx that qualified on pole. Next up was the Alpine-Renault A443 of Jean-Pierre Jabouille / Patrick Depailler followed by Schurti / Stommelen with the Moby Dick.
The Wollek / Barth 936 was fourth. Didier Pironi / Jean-Pierre Jassaud started fifth in their Alpine-Renault A442B while Haywood / Gregg / Joest lined up sixth in the other 936 and Jean-Pierre Jarier / Derek Bell qualified seventh in their Alpine-Renault A442A.
The build-up had not been without problems for the 935 / 78; halfway through the second day of practice, 006 blew a piston and needed a complete engine rebuild. The problem had arisen as the car had been driven to the circuit in traffic as part of a misguided publicity stunt. 006 got caught in gridlocked traffic and prolonged low speed running overheated the engine which caused it to blow in practice.
The start of the race saw Schurti drop to fourth off the line. For the first couple of hours he was forced to drive conservatively to run-in the freshly rebuilt engine.
Nevertheless, at the three hour mark, chassis 006 was sixth. Meanwhile, the Alpine-Renaults were in first and second as the 936s had experienced early problems.
As night fell, the 935 / 78 was fifth. It then dropped back to sixth in the early hours of Sunday morning having been passed by one of the recovering 936s.
Unfortunately, 006 had a troubled second half of the race that meant it was unable to fulfil its potential.
Shortly after 4am the car was delayed as new fuel pump had to be fitted. It then had to come in for a stuck throttle, leaking radiators, a loose windscreen, a replacement distributor and a replacement injection pump. Additionally, a persistent oil leak meant it needed a complete refill every 16 laps (the minimum distance permitted).
In total, chassis 006 spent nearly three hours in the pits.
Miraculously, Stommelen and Schurti managed to finish eighth overall despite having made around 35 pit stops. It was the fourth 935 home.
1978 Vallelunga 6 Hours
Although Porsche had vowed to leave the 1978 World Sportscar Championship to its customer teams, the factory squad made a surprise appearance at the season-ending Vallelunga 6 Hours (September 3rd).
Jacky Ickx joined Manfred Schurti in the 935 / 78.
The first qualifying session was dominated by Bob Wollek’s Kremer 935 after chassis 006 suffered an acute understeer problem. However, following some set-up tweaks, Ickx came out after lunch and sliced five seconds off his best time and claimed pole position by seven-tenths-of-a-second.
The Georg Loos 935s of John Fitzpatrick / Klaus Ludwig and Toine Hezemans / Hans Heyer rounded out the top three followed by another trio of 935s in fourth through sixth. The works BMW 320i Turbo of Peterson / Stuck qualified seventh.
Ickx made the best start and rapidly established a big lead over Ludwig, Hezemans and Pescarolo (Kremer).
At mid-distance, 006 had healthy lead, but it would need to make an extra stop over its rivals. Meanwhile, the Kremer entry of Wollek / Pescarolo was still on same lap ready to pounce in the event of any problems.
With just ten minutes to go, it seemed that Ickx / Schurti would take Porsche’s second World Championship win of the year. However, disaster struck when Ickx coasted into the pits with a snapped fuel-injection pump belt and retired.
Pescarolo and Wollek took the win for Kremer while the pair of Georg Loos cars came in second and third.
1978 Norisring Trophy
Two weeks after the disappointment of Vallelunga, Porsche ran the 935 / 78 at the annual Norisring Trophy which was unusually held in mid September instead of June as a result of a fixture clash with the football World Cup.
The 200 mile race was a big money event supported by a round of the 1978 Deutsche Rennsport Meisterschaft.
Jochen Mass was originally scheduled to drive 006, but after he picked up an injury elsewhere, Jacky Ickx was drafted in to replace him.
Ickx had set the fourth fastest time in qualifying when the car emitted a huge cloud of smoke; a holed piston necessitated an overnight engine rebuild.
Toine Hezemans secured pole (Georg Loos) followed by Bob Wollek (Kremer) and Klaus Ludwig (Georg Loos).
In the race, Ludwig took the lead followed by the 935s of Hezemans, Schurti (Max Moritz), Wollek and Fitzpatrick (Georg Loos). Ickx dropped to sixth off the line. He stayed in sixth until lap 14 when severe handling problems caused by a broken brake balance bar forced him to retire just past quarter distance.
That was the last time the 935 /78 was seen in frontline competition.
Post Season
Although Porsche had made tentative plans to build a full ground effect 935 for 1979, these plans were abandoned when Martini decided taking a sabbatical from motor racing sponsorship.
Chassis 006 went straight into the Porsche Museum while the unfinished 007 was placed in storage.
Text copyright: Supercar Nostalgia
Photo copyright: Porsche - https://www.porsche.com
