Guide: Porsche 935/76
Background
For 1976, new sports car racing regulations were introduced.
Group 6 was for out-and-out Prototypes with no minimum production requirement.
Groups 4 and 5 were open to production-based GT cars once a homologation requirement of 400 cars had been met within a 24 month timeframe.
Group 4 allowed straightforward modifications such as wider wheels / tyres and uprated engines.
Group 5 was for more highly modified machinery that had already been homologated in Groups 1 to 4. Extensive upgrades were permitted, but the donor car’s bonnet, roof and doors had to be retained.
To qualify for Group 4 and 5, Porsche created the turbocharged 930 road car which proved so popular it became a permanent fixture in the company’s model line up.
Group 5 was supposed to become the premium class of the World Sportscar Championship in 1975. However, it was postponed for a year owing to a lack of manufacturer support.
As it turned out, most firms wanted to continue to run prototypes which left the governing body in a tricky position.
The FIA ultimately made the diplomatic decision to organise two stand-alone championships: one for Group 6 cars (the 1976 World Sportscar Championship) and one for Group 5 and Group 4 cars (the 1976 World Championship for Makes).
The only time Prototype and GT cars ran together in 1976 was at the Le Mans 24 Hours which had lost its World Championship status as a result of the ACO’s decision to implement a controversial fuel efficiency formula.
Having invested heavily in their Group 5 programme, Porsche ploughed on. The resultant 935 would take the challenge to BMW’s Group 5 CSL which had won the 1975 IMSA championship.
However, Porsche also decided to create a car to contest the Group 6 contest: the 936.
The 935 and 936 would run with backing from Martini in 1976.
Porsche’s customers were supplied with the Group 4 934.
Chassis
The 935 retained the same steel monocoque bodyshell used by the 930 and 934.
Suspension-wise, it used MacPherson struts at the front, double wishbones at the rear and gas-filled Bilstein dampers all round. The whole thing was custom fabricated, fully adjustable and riddled with lightweight components.
Anti-roll bars were fitted at either end. The one at the rear was adjustable from within the cockpit.
Anti-dive was also employed.
The dual circuit brake system was imported from the 917 and featured ventilated discs with four-piston calipers at each corner.
Enormous new centre-lock BBS wheels were shod with Dunlop tyres. The front rims had a 16-inch diameter and were 10.5-inches wide. The backs had a 19-inch diameter and were 15-inches wide.
Compared to the standard 930, track was 66mm wider at the front and 46mm wider at the rear.
Engine & Gearbox
At the heart of the new model was a turbocharged Type 930/72 engine.
As the Group 5 regulations had a four-litre limit, displacement was scaled back from 2994cc to 2856cc. When the 1.4 multiplier for turbocharged engines was taken into account, this gave a swept volume of 3999cc.
The cubic capacity was reduced thanks to a bore reduction of 2.6mm (92.4mm instead of 95mm). Stroke stayed at 70.4mm.
Although the 935 engine was another all-alloy, dry-sumped, single overhead camshaft unit with two valves per cylinder, just about the only parts it shared with the standard 930 were the crankcase and crankshaft.
Special parts included a horizontal cooling fan, titanium connecting rods, forged steel rocker arms, twin plug ignition and mechanical plunger-type fuel-injection.
The compression ratio was 6.5:1.
Boost pressure for the single KKK turbo could be adjusted from the cockpit. It typically varied from 1.2 bar to 1.5 bar. An air-to-air intercooler was initially employed.
1.4 bar was normally used for a six hour endurance race. In this configuration, peak output was around 590bhp at 8000rpm and 433lb-ft at 5400rpm.
Transmission was via the same short-shift four-speed oil-cooled gearbox found in the 934. A spool for permanently locking the rear driveshafts meant there was no need for a limited-slip differential.
Titanium driveshafts were fitted with constant velocity joints and rubber couplings.
Bodywork
Porsche exploited the somewhat ambiguous Group 5 bodywork regulations to the limit.
Because the regulations did not specify that production-spec. headlights and front fenders had to be retained, Porsche produced two different single-piece noses to test the rule makers.
One retained production-style wings with conventional 911 headlights.
The other was the Flachbau which used flattened fenders upon which banks of louvres were cut to allow high-pressure air to escape from the wheel wells. In this instance, the headlights were moved to the front apron and mounted behind clear Plexiglas covers.
Plexiglas was also used for the side and rear windows. A standard glass screen was installed at the front.
Aside from the steel roof, the bodywork was fabricated entirely from fibreglass.
Massive wheelarch extensions were required to cover the enormous BBS rims.
A huge split-level spoiler was installed at the back. It housed the intercooler which was fed by intake slots ahead of the rear wheels.
Interior
Inside, the cockpit was suitably pared down.
An aluminium rollcage was installed along with a single bucket seat trimmed in fire-retardant upholstery. The 930’s familiar five-gauge instrument binnacle was retained although the dash was now left in bare metal.
A toggle switch for the turbo boost was located under the centre of the dash.
Weight / Performance
The 935 weighed in at 880kg which was well below the 970kg class minimum. This enabled Porsche to strategically position lead ballast and attain an ideal 40/60 front/rear weight distribution.
Top speed was 209mph and 0-62mph took 3.2 seconds.
1976 Season
Testing began in late 1975. It continued at Weissach and Paul Ricard for several weeks.
Porsche unveiled the 935 and 936 to select members of the press at a Weissach press conference in the second week of March. Jacky Ickx and Jochen Mass were both in attendance; they would handle the lion’s share of driving in 1976.
However, both Ickx and Mass had Formula 1 contracts for the season ahead (Ickx with Wolf-Williams and Mass with McLaren). On the occasions that sports car races clashed with F1 events, Rolf Stommelen and Manfred Schurt would be called upon.
The 1976 World Championship for Makes comprised seven events that ran for either six hours or 1000km. Porsche planned to contest all seven races as well as the independent Le Mans 24 Hours.
A single car attack was planned for the season ahead but, to counter a late-season charge from BMW, Porsche expanded to a pair of 935s for the final two races of the year.
1976 Mugello 6 Hours
The championship kicked off with the Mugello 6 Hours on March 21st. Porsche took a new car to Italy (chassis 002) while the original test car (001) was kept as a back up.
Opposition in the Group 5 class arrived in the form of a hastily built Kremer 935 which, once sorted, really began to fly. There were also 3.5-litre BMW CSLs from Alpina, Schnitzer and Hermetite. A number of highly modified privateer 911 RSRs ran in the Group 5 category as well. Quickest of these was the Joest Racing entry.
Unsurprisingly, the combination of Ickx, Mass and a works 935 proved fastest over both days of qualifying. The Martini car clocked a time 2.25 seconds faster than Bob Wollek / Hans Heyer in the Kremer 935.
Third through fifth spots went to the BMW CSLs. The Schnitzer example of Dieter Quester / Albrecht Krebs / Brian Redman was third, the Hermetite car of John Fitzpatrick / Tom Walkinshaw was fourth and the Alpina machine driven by Sam Posey / Harald Grohs / Hughes de Fierlant lined up fifth.
In the race, the Martini and Kremer 935s powered ahead from the rolling start. By lap ten, they had a 15 second advantage over the Hermetite BMW and, for the next couple of hours, they continued to pull away from the rest of the field.
The Kremer 935 was just about able to hang on and briefly led when the Martini car picked up a puncture around the two hour mark. However, Ickx and Mass were soon back in the lead.
When the Kremer machine lost seven minutes to have a rubber driveshaft seal replaced at mid-distance, the works 935 found itself with a lap lead over the Hermetite BMW. The Alpina CSL was a further two laps in arrears and Kremer lay fourth after their long stop.
Despite a problem with leaking wheel rims, which meant several unscheduled stops for new tyres in the second half of the race, Ickx and Mass eventually went on to take a comfortable win.
The Schnitzer BMW of Quester / Krebs / Redman looked set for second until it lost oil pressure in the final minutes which allowed the Kremer 935 of Wollek / Heyer to regain the runner’s up spot. Third went to the GT class winning Egon Evertz Porsche 934 co-driven by Leo Kinnunen.
1976 Vallelunga 6 Hours
Two weeks later, the championship moved south to Vallelunga for another six hour race (April 4th). On this occasion the Porshes and BMWs were joined by a works Lancia Stratos Turbo and a De Tomaso Pantera that had been built by Sala Marverti for Scuderia Brescia Corse.
Ickx and Mass took pole by 2.3 seconds from the Kremer 935 of Wollek / Heyer. Next up was the Marlboro-backed Lancia of Vittorio Brambilla and Carlo Facetti which was followed by three BMWs (Alpina, Schnitzer and Hermetite). The De Tomaso started back in 15th.
Porsche opted to use the conventional front end for the race and Ickx / Mass simply drove away from the rest of the field. All the factory mechanics had to do was fill the car up with fuel, change the tyres and add some oil.
As for the competition, the Kremer 935 retired in the first hour with gearbox trouble. The works Stratos kept up a good second position until 4.5 hours in when it too retired with transmission problems.
The Alpina BMW struggled to a second place finish after gearbox trouble and a broken crankshaft damper slowed its pace. Posey / Grohs / de Fierlant finished a distant 16 laps behind the winning Porsche.
Kenneth Leim’s privateer 911 Carrera RSR co-driven by Kurt Simonsen finished third and the Hermetite CSL of Fitzpatrick / Walkinshaw finished was fourth (27 laps down).
Porsche's dominance was already beginning to ruffle feathers in rival camps.
1976 Silverstone 6 Hours
At the Silverstone 6 Hours on May 5th, BMW debuted their brand new works CSL Turbo which would go on to appear intermittently during the rest of the season.
In practice, Ickx and Mass found the Flachbau front end generated too much downforce so they quickly switched to the conventional nose as used at Vallelunga.
The Martini 935 took pole for the third consecutive race. Ronnie Peterson / Gunnar Nilsson started second in the works CSL Turbo (just over a second behind). Wollek / Heyer qualified third in the Kremer 935 while in fourth spot was the Egon Evertz / Leo Kinnunen Porsche 934 which was running the new 934/5 kit.
The 934/5 kit comprised wheelarch extensions and bigger spoilers to take the car out to Group 5 trim.
In fifth, sixth and seventh positions were the normally aspirated Schnitzer, Alpina and Hermetite BMW CSLs.
Unfortunately, Ickx only got to Becketts on the opening lap before the clutch friction plate disintegrated. He tried to repair the car out on the circuit with advice from the mechanics but it was eventually decided the drivers should push 002 back to the pits. The pit crew then struggled to remove the gearbox and fit a new clutch. The car eventually resumed just before the two hour mark.
Ickx’s problem had allowed Peterson to take the early lead for BMW. However, soon after the first hour, the Swede dropped out with gearbox trouble.
At the two hour mark, a broken turbo cost the Kremer team 15 minutes and dropped them well down the order having previously been leading.
The race was ultimately won by the Fitzpatrick / Walkinshaw Hermetite BMW which finished barely a second ahead of Wollek / Heyer in the Kremer 935. Kinnunen / Evertz were third in their 934/5.
Ickx / Mass finished last in tenth position overall.
The FIA Acts
After Silverstone, the FIA dealt Porsche a bitter blow. The 935’s air-to-air intercooler was deemed illegal because it meant the standard 930 engine cover did not fit which was prohibited under the Group 5 regulations. Porsche were forced to install a more compact air-to-water layout instead.
The FIA also dictated a new space cam be developed for the fuel-injection pump. This and the intercooler issue resulted in an engine that was initially down on torque and less reliable.
Manfred Schurti spent a week testing the new set up prior to round four at the Nurburgring. He and Rolf Stommelen would take the wheel of 002 for the race in Germany because Ickx and Mass would both be attending the Monaco Grand Prix.
1976 Nurburgring 1000km
The Nurburgring 1000km took place on May 30th. BMW failed to attend with their CSL Turbo which left Schnitzer, Alpina and Hermetite to take the challenge to Porsche.
The works 935 set a lap time nearly 20 seconds faster than the Kremer machine around the daunting 23km course. During the first session, the boost pressure had been cranked up to 1.45 bar, but the engine broke a piston and had to be changed overnight. The boost was reduced to 1.2 bar for the second day’s practice.
Third and fourth spots on the grid went to the Kannacher and Gelo Racing Team 934/5s. The Hermetite and Alpina CSLs were fifth and sixth, a Max Moritz Porsche 934 was seventh and the Alpina CSL lined up eighth.
In the race, Stommelen pulled away at around ten seconds per lap. Wollek wasn’t able to respond in the Kremer car as he had lost part of his front spoiler and had a job holding off the fast 934/5s behind him.
On lap seven, Stommelen came in to hand over to Schurti. Schurti resumed still in the lead but chassis 002 only lasted until the descent to the Flugplatz before the engine died as a result of a broken distributor arm.
Around the same time, the Kremer 935 stopped with a broken driveshaft.
Both cars were able to get back to the pits, but they were ultimately disqualified for receiving outside assistance.
The 934/5s left in the race were unable to resist the challenge from Schnitzer. The BMW of Albrecht Krebs and Dieter Quester came home nearly four minutes ahead of Toine Hezemans / Tim Schenken in the Gelo 934/5. Third spot went to the Max Moritz 934 driven by Helmut Kelleners / Reinhard Stenzel / Derek Bell.
Victory in Germany allowed BMW to recover yet more ground in the championship.
1976 Le Mans 24 Hours
Next up was the Le Mans 24 Hours for which Porsche were permitted to run the 935 with its original air-to-air intercooler.
Porsche attended with a three car team. It comprised a 935 for Rolf Stommelen / Manfred Schurti plus a brace of 936s for Jacky Ickx / Gijs van Lennep and Reinhold Joest / Jurgen Barth. Jochen Mass was absent in order to race at the Swedish Grand Prix. Ickx skipped the F1 contest at Anderstorp to compete at Le Mans instead.
The race took place over June 12th and 13th. Group 5 opposition to the Martini crew came in the shape of Kremer’s 935 plus myriad uprated 934s and 911 RSRs. BMW were in attendance with a works CSL Turbo Art Car which was supported by the factory-backed Schnitzer, Alpina and Hermetite machines.
In the interest of reliability, Porsche ran the 935 at a reduced boost pressure of 1.2 bar. Chassis 002 also arrived with smaller spoilers, supplementary lights and special gearing which enabled it to hit 209mph down the Mulsanne Straight.
Stommelen / Schurti qualified the Martini 935 in third position. Ahead of it was the pole-starting Jabouille / Tambay / Dolhem Alpine-Renault A442 Turbo followed by Ickx / van Lennep in the faster of the two 936s.
In the race, Brian Redman blasted past Schurti on the opening lap in his CSL Turbo Art Car. However, the BMW soon headed for the pits and the Martini 935 retook the lead in Group 5.
With an hour gone, the two works 936s were first and second, the pole-starting Alpine-Renault was third and the 935 was fourth. An early stop for Alpine then meant Porsche held first, second and third at the 30 lap mark.
These were still the positions after three hours of racing by which time the 935 was a lap down on the lead pair. However, shortly after 8pm, the 935 suffered an alternator belt failure which dropped it to sixth.
At 9pm, Andre Haller lost control of his GT class Datsun 260 Z. The car slid on to the grass verge at the kink near the end of the Mulsanne Straight. It crashed into the barrier and caught fire.
Poor Andre Haller died en route to the hospital.
Meanwhile, the Martini 935 dropped further down the leaderboard overnight after part of the rear suspension fell apart when a mounting broke and damaged the bodywork. Upon re-assembly, the car rejoined ninth but progress was further hampered by a couple of punctures.
Come 6am, Stommelen / Schurti had regained fifth spot and the Joest / Barth 936 had stopped with transmission failure. Ickx / van Lennep led.
Just before 10am, the 935 was back in the pits with ignition trouble and, at midday, a new turbo had to be fitted.
Despite a troubled run, Schurti / Stommelen came home fourth overall to win the Group 5 category.
Only one of the BMWs made it to the finish. It placed tenth overall and fourth in class behind a couple of privateer Group 5 911 RSRs.
Outright victory went to the Martini 936 of Jacky Ickx / Gijs van Lennep which finished eleven laps clear of the Jean-Louis Lafosse / Francois Migault Mirage GR8. The De Cadanet Lola T380 of Alain De Cadanet / Chris Craft finished third.
All things considered, Le Mans 1976 proved a very satisfactory event for Porsche who took their third outright win at la Sarthe.
1976 Osterreichring 6 Hours
The World Championship for Makes resumed on June 27th with round five: the Osterreichring 6 Hours.
Although there was no F1 race that weekend, Jacky Ickx was partnered by Manfred Schurti instead of Jochen Mass.
In qualifying, the Martini 935 took pole by nearly four seconds from its nearest competitor.
Lining up alongside on the front row of the grid was the Kinnunen / Evertz Porsche 934/5 which was followed by the Alpina CSL of Peterson / Grohs / de Fierlant.
The Schnitzer CSL of Questor / Nilsson qualified fourth, Haldi / Zbinden were fifth in the GVEA Porsche 934 and Fitzpatrick / Walkinshaw started sixth in the Hermetite CSL.
Because Kremer’s usual drivers, Wollek and Heyer, were racing elsewhere, a directive from the Porsche factory saw Derek Bell and Vern Schuppan invited to drive. In the face of stiffer than expected opposition from BMW, Porsche decided to supply Kremer with a works prepared engine for the rest of the year. However, practice was fraught with problems and Bell / Schuppan qualified down in seventh.
Unfortunately, the works Lancia Stratos Turbo failed to make what would have been its second appearance of the year after it caught fire in practice.
With the race underway, Ickx rocketed clear in the works 935 and Bell began to pick off the BMWs in the Kremer machine. After a few laps, Bell had also passed Kinnunen to occupy second.
At the end of the first hour, Ickx still led Bell, but the Martini and Kremer pit crews were conscious they would have to make two stops more than the BMWs as a result of their increased turbo pressure.
Ickx continued to pull away until the two hour mark when he came into the pits with a rough sounding engine. A bent valve put it him of the race. Having yet to do a stint at the wheel, Schurti joined Kinnunen in the fast Egon Evertz 934/5, but they were duly disqualified for an illegal driver change.
After the Martini 935 dropped out, Kremer took over at the head of the field and looked set for victory.
Then, with an hour to go, Bell came into the pits; the input shaft from the throttle to the turbo had broken. It was changed, but the race was lost and Bell / Schuppan came home fourth.
BMW took their third win in a row. Questor / Nilsson emerged victorious for Schnitzer while Fitzpatrick / Walkinshaw were a close second for Hermetite. Best of the Porsches was the GVEA 934 of Haldi / Zbinden in third.
Porsche and BMW headed to the USA for the penultimate race with just four points between them.
1976 Watkins Glen 6 Hours
With the very real possibility of losing the championship, Porsche sent two Martini 935s across the Atlantic for the Watkins Glen 6 Hour race on July 10th.
As Kremer would not be making the trip, Porsche loaned a 935 engine and gearbox to the Egon Evertz crew for use in their 934/5.
BMW would be represented by cars from Alpina and Hermetite plus another from the IMSA-winning Brumos team.
Mass / Ickx took pole in chassis 002 while Stommelen / Schurti lined up second in 001. Kinnunen / Hezemans / Evertz qualified third in the tricked out 934/5. The Hermetite CSL of Fitzpatrick / Walkinshaw / Redman lined up fourth alongside which should have been the Keyser / Wachs Chevrolet Monza, but this car was withdrawn before the start. Gregg / Haywood qualified sixth in the Brumos CSL and Peterson / Quester were seventh in the Schnitzer example.
In the race, Mass and Stommelen pulled away from the rest of the field to lead in formation. However, when Stommelen picked up a puncture with half an hour gone, 001 dropped to third.
Stommelen and Schurti eventually recovered their original position from the Evertz hot rod. They looked set for the runner’s up spot until the lead 935 of Ickx / Mass lost several minutes in the pits at two thirds distance; its rear brake pads had worn down to nothing and the bare backing plate had welded itself to the calipers which locked the wheels.
As a precaution, the Stommelen / Schurti car was brought in for a pad change. It emerged in the lead and ran without trouble to the finish.
The Ickx / Mass car lost eleven minutes while new discs and calipers were fitted. It resumed in sixth, some four laps down on the sister car. Ickx tore through the field to take third at the chequered flag.
Second spot went to the Kinnunen / Hezemans / Evertz Porsche with its 935 engine and ‘box.
Gregg / Haywood finished fourth for Brumos and Peterson / Questor were fifth for Schnitzer.
Porsche’s victory at the Glen ensured the title would be decided at the last race of the year: the Dijon 6 Hours on September 4th.
1976 Dijon 6 Hours
Once again, two Martini 935s were entered: 002 for Ickx / Mass and 001 for Stommelen / Schurti.
After their absence at Watkins Glen, Kremer returned to the fray.
The works BMW team were also on hand with a CSL Turbo for Peterson / Nilsson.
Peterson took pole in the BMW with a lap time half a second quicker than the Ickx / Mass 935 which lined up second. Schurti / Stommelen were third in the other Martini 935 and Wollek / Heyer were fourth for Kremer.
Fifth spot went to the Alpina CSL of Nilsson / Grohs and the Ervertz / Kinnunen 934/5 hot rod qualified sixth. The Hermetite and Schnitzer CSLs lined up eighth and ninth behind the Haldi / Muller Porsche 934/5.
When the flag dropped, Peterson led into the first corner followed by the Porsches of Ickx, Schurti and Wollek.
Ickx was determined to hold on to Peterson who had his boost turned right up; the lead pair soon began to pull away from Schurti and Wollek and, for the next 30 laps, Peterson and Ickx circulated nose to tail.
On lap 34, Peterson lost all drive. Ickx went through as the turbocharged BMW headed slowly to pits. Once there, the diff locked up completely and the car was retired; Porsche now held the first four positions.
At the two hour mark, the Martini cars were 35 seconds apart.
As the race approached its mid point, Schurti started to make an impression on Ickx. He cut the Belgian’s lead down to seven seconds before team manager, Norbert Singer, told him to cool it. Thereafter, the works cars ran ten seconds apart with the Kremer car a further 20 seconds down the road. Everyone else had been lapped.
With five hours gone, the lead car came in for a pad change after Ickx’s early chase with Peterson had taken the life out of them.
This looked to have handed victory to the sister car, but with 40 minutes to go, Stommelen came in for an unscheduled stop; a brake line had fractured and the fluid had drained out. Fortunately, because of the dual circuit system, the car still had stopping power at the rear.
The problem took nine minutes to fix and dropped Stommelen / Schurti to third with no hope of catching the Kremer entry.
Ickx / Mass took the win and Porsche secured the 1976 World Championship of Makes with a ten point margin.
1977 Daytona 24 Hours
For 1977, the works team developed a twin turbo 935. However the new car wasn’t ready in time for the season-opener at Daytona so Porsche wheeled out chassis 002 instead.
The well-used car once again qualified on pole and led the race until an hour was lost to repair damage caused by a puncture.
Drivers Ickx and Mass hauled 002 back into second place, but a second tyre failure caused the car to have a big accident after which it was retired from competition duty.
1977 Mugello 6 Hours
Another single turbo 935 was then called upon for round two of the 1977 championship at Mugello. It appeared alongside the new twin turbo derivative.
Chassis 003 was a previously unraced example. It was taken to Mugello for Rolf Stommelen and Manfred Schurti. The brand new twin turbocharged 935 (chassis 004) debuted in the hands of Jochen Mass and Jurgen Barth.
Qualifying saw Mass go fastest with 004 while Schurti was second in 003.
During the opening stages of the race, Mass led from Stommelen with Bob Wollek’s single turbo Kremer 935 close behind.
However, as the first hour progressed, Wollek passed Stommelen and slowly pulled away from 003.
At the 90 minute mark, light rain began to fall and both of the works cars came in for wets. Fitzpatrick stayed out and inherited the lead for Kremer.
Barth re-took the top spot in 004 half an hour later, but was beginning to suffer brake fade so came in for new pads. Fitzpatrick went passed just as Barth was coming out of the pits.
Unfortunately, the German had forgot to prime his pads and arrived at the first corner brake-less. Barth ploughed into the back of the Kremer Porsche and took both cars out of the race.
This left Stommelen and Schurti with a comfortable three lap lead in the single turbo car.
For the remaining three hours, 003 purred around the track, increasing its advantage lap after lap.
Stommelen and Schurti eventually finished six laps clear of the second-placed Jolly Club customer 935.
Chassis 003 was subsequently retired from competition duty.
Porsche ultimately went on to win the 1977 championship by a massive 84.5 point margin.
Text copyright: Supercar Nostalgia
Photo copyright: Porsche - https://www.porsche.com
