Guide: Porsche 911 2.2 Carrera RSR Turbo
Background
In early February 1974, Porsche announced they had discontinued their Group 7 racing programme with the 917. Cost had a part to play, but the new company Chairman, Ernst Fuhrmann, also held a desire to focus on racing cars that bore a greater resemblance to production models.
With some of the most powerful turbocharged engines ever seen, Group 7 Porsche 917s had toppled the formidable McLaren team to win the Can-Am Championship in 1972 and 1973. On European soil, they also secured the Interserie titles of 1972 and 1973.
These 917s were almost always run by Porsche satellite teams such as those of Roger Penske, Vasek Polak, Brumos and Willi Kauhsen. However, the works team did not sit idly by. Under the Martini Racing banner, Porsche successfully campaigned an experimental batch of 911 Carrera RSRs in the 1973 World Sportscar Championship.
With attention no longer being diverted elsewhere, for 1974, the works 911 programme was stepped up a gear.
The result was the first turbocharged 911: the Carrera RSR Turbo.
It would pave the way for a production 911 Turbo (the 930) which would in turn be used to homologate a racing variant (the 935) for the FIA’s hotly anticipated Group 5 Silhouette regulations set to be introduced for 1975. A less highly tuned Group 4 iteration (the 934) would also be built.
The RSR Turbo was a rolling laboratory for turbo technology and looked about as far removed from the road-going 911 as one could imagine.
Built for the existing Group 5 Prototype class, it was not constrained by production-based regulations and was thus able to run with super wide wheels and enormous spoilers.
However, as a Group 5 entry, it would be up against conventional Prototypes from Matra (MS670), Alfa Romeo (33/TT/12) and Mirage (GR7) which meant class wins were unlikely.
Meanwhile, the Group 4 category was left to Porsche’s customer teams in 1974. For this, Porsche supplied the 911 3.0 Carrera RSR to anyone with sufficient funds.
Unlike the customer 1974 RSR, the works RSR Turbo was modified almost completely out of recognition. Little other than the floor pan, roof and basic mechanical bits such as crankcase and gearbox remained in what was a foretaste of the incoming Silhouette formula where radically modified machines retained not much more than the original engine block, engine position and silhouette of the base model.
Chassis
The RSR Turbo’s galvanised steel bodyshell most notably featured a new bolted aluminium rear spaceframe to support the engine, transmission and rear suspension.
New coil sprung suspension replaced the standard torsion bar arrangement and allowed Porsche to remove the heavy duty crossmember that normally anchored the suspension and supported the engine.
The suspension was specially fabricated with improved geometry. Titanium coil springs and Bilstein gas-filled dampers were fitted all round along with adjustable anti-roll bars at either end. The lower front wishbones had anti-dive built into the pick-up points.
Cross-drilled and ventilated discs with four piston calipers and titanium hubs were lifted from the 917. Brake balance was cockpit-adjustable for both axles.
The magnesium centre-lock wheels had a 10.5-inch diameter and were shod with Dunlop Racing tyres. They measured 15-inches wide at the front and an extraordinary 17-inches wide at the rear.
Engine & Gearbox
As Group 5 had a three-litre engine limit and turbo boost multiplier of 1.4, Porsche needed an engine with a maximum displacement of 2150cc. They settled on 2143cc thanks to a special motor that was de-bored to 83mm and de-stroked to 66mm.
This Type 911/76 engine used the most exotic components available to ensure it was light, powerful and reliable.
Nikasil-lined cylinders and heads were fitted along with four instead of three bearing camshafts. There were also new pistons, titanium connecting rods, titanium inlet valves, Nimonic steel exhaust valves and magnesium crankcases.
For maximum durability, a standard forged steel crankshaft from the old two-litre 911 was employed and the compression ratio was set at a conservative 6.5:1.
The turbocharger was supplied by KKK (Kuhnle, Koppe and Kausch AG). It was centrally mounted at the rear of the engine on an aluminium crossmember that formed part of the rear subframe. Exhaust gasses were diverted away from the turbo by a Garrett wastegate. Boost was adjustable via a dash-mounted switch in the cockpit.
Bosch supplied the K-Jetronic mechanical fuel-injection, twin plug ignition and single distributor. Oil pumps from the Porsche 908 were installed.
Output was initially quoted as 450bhp at 8000rpm but progress was rapid in this regard. By the middle of 1974, a Type 911/78 engine was available which produced 500bhp at 7600rpm and 405lb-ft at 5400rpm.
Despite such prodigious numbers, Porsche opted to stick with the five-speed Type 915 gearbox as fitted to the standard 1974 RSR. They knew it would be at the limit of its torque capacity but had no realistic alternative.
Other special equipment included a ZF limited-slip differential and titanium driveshafts.
Bodywork
Visually this was the most extreme 911 yet.
Dramatic wheelarch extensions were stretched over the enormous new rims while at the rear, a custom engine lid was used to mount an elaborate F1-style spoiler on two swept pylons. The engine cover was home to a gigantic NACA duct, airflow to which was smoothed by a flush rear window instead of the standard recessed item.
By deleting the spare wheel and moving the fuel tank from underneath the front lid to inside the passenger compartment, Porsche were able to integrate a new front apron with large brake cooling ducts alongside an enormous radiator intake.
Wafer thin fibreglass was used to fabricate the front and rear deck lids, the fenders, doors and aprons.
Interior
In addition to the aluminium-encased fuel tank mounted behind the front seats, the RSR Turbo came with a rudimentary new crackle-black dash and a lightweight aluminium rollcage.
Weight / Performance
Weight was initially around 820kg which had been further reduced towards 750kg by the summer of 1974.
Top speed was 193mph and 0-62mph took 3.2 seconds. With a 30/70 front-to-rear weight bias and old-school turbo delivery, the RSR was a real handful to drive.
Production
Porsche constructed four RSR Turbos, three of which were built from scratch (R9, R12 and R13) plus one mule (R5, ’The Tank’) which was assembled from a works 1973 RSR with a standard chassis.
All four were painted silver and emblazoned with Martini graphics.
1974 Le Mans Test
The new Porsche was first seen in public at the annual Le Mans Test on March 24th 1974. Two cars were taken: R9 for Gijs van Lennep / Herbert Muller and R12 for Helmuth Koinigg. Both R9 and R12 ran without the air-to-air intercooler which added 50bhp.
All three drivers found the handling less than perfect with too much downforce on the front wheels. Koinigg nevertheless posted sixth fastest time with van Lennep / Muller back in seventh.
Just behind the RSR Turbos in eighth spot was the brand new Ligier JS2 Maserati which was similarly a GT-based Group 5 Prototype.
Fastest overall was the Alfa Romeo 33/TT/12 of Arturo Merzario.
1974 Le Mans 4 Hours
The Le Mans Test weekend closed with a four hour race.
Grid slots were dictated by test times but, because of absentees for the race, Koinigg (who was joined by Manfred Schurti) started fourth and van Lennep / Muller lined up fifth.
Neither of the RSR Turbos finished.
First to go was the Koinigg / Schurti machine which retired with a broken rocker arm after four laps.
Van Lennep / Muller went out after 30 laps with turbo problems.
1974 Monza 1000km
The RSR Turbos were then present for the opening round of the 1974 World Sportscar Championship on April 25th: the Monza 1000km.
Two of the cars were taken to Italy: R12 for van Lennep / Muller to race and R9 as a spare. The engine in R12 reportedly had around 480bhp.
Both practice days were wet which meant the Porsche was unable to use all of its power. As a result, Muller and van Lennep only qualified twelfth fastest, two spots behind the solitary works Ligier.
Race day also started cold and wet but, once proceedings got underway, the track quickly dried out.
The RSR Turbo ran like a train; it proved fast and reliable except for an extended stop when the driver’s door wouldn’t shut.
R12 eventually finished fifth overall, nine laps behind the winning Alfa Romeo Tipo 33/TT/12 of Arturo Merzario / Mario Andretti. Alfa took a famous 1-2-3 on home soil after both Matras retired from the lead.
Shortly before the end of the race, Swiss privateer, Silvio Moser, crashed into a stationary car that had been abandoned earlier on. Moser’s Lola T294 was split in two between the engine and rear bulkhead. Moser suffered serious injuries including a cracked skull and a broken leg.
Silvio Moser died on May 26th without ever regaining consciousness.
1974 Spa 1000km
Just a few days after the race at Monza, the World Championship moved on to Belgium for the Spa 1000km (May 5th).
Alfa Romeo decided not to attend owing to a combination of the dangerous 14km track and poor starting money.
Ligier arrived with a brace of JS2s boasting further uprated Maserati engines. Porsche ran just the one RSR Turbo for Muller / van Lennep (R12).
Conditions were cold but dry.
One of the JS2s was damaged beyond repair after a crash in practice while the remaining example outqualified the RSR Turbo again. The Ligier would start fifth and the Porsche sixth.
There was a high attrition rate in the race but Muller and van Lennep soldiered on to finish third.
The car’s only problem had been the need for two new left rear tyres after the rear body panels started to rub onto the tyre’s outer edge. Once again, the turbo engine proved a model of reliability.
Victory went to the Jacky Ickx / Jean-Pierre Jarier Matra MS670C with Derek Bell / Mike Hailwood second in the Gulf-backed Mirage GR7. The solitary Ligier only lasted six laps before it blew a head gasket.
1974 Nurburgring 1000km
Two weeks after Spa, the next round of the 1974 World Sportscar Championship took place: the Nurburgring 1000km (May 19th). Although dubbed a 1000km race, the event was actually shortened to 750km in light of the Oil Crisis.
Porsche raced two RSR Turbos as they would do for the subsequent three events (Imola, Le Mans and Zeltweg). Muller / van Lennep were in the car they shared at Monza and Spa (R12) while the spare (R9) was prepared for Helmuth Koinigg and Manfred Schurti.
Ligier stayed away from the Nurburgring in preparation for Le Mans while Matra, Alfa Romeo and Mirage were all out in force.
During the Saturday practice session, van Lennep got it all wrong as he passed another car over the crest of Pflanzgarten. The Porsche landed sideways and before van Lennep could do anything about it, the back shot around and side swiped the barrier.
R12 was badly damaged and the mechanics had to work frantically through the night to fix it.
The circuit layout was not well suited to the RSR Turbos which were difficult to keep on boost.
Muller / van Lennep qualified twelfth fastest and Schurti / Koinigg were 14th. However, this was still appreciably quicker than the best standard 911 RSR (that of the Georg Loos team, which started 25th).
The race began under clear blue skies with Muller pushing and shoving right from the start. This continued throughout the race and both RSR Turbos tangled with various cars over the next few hours. Rivals suggested the big rear wing must have obscured the Porsche driver’s vision.
By the end, the Martini cars looked decidedly second hand. The Muller / van Lennep machine was delayed by a long session in the pits but still managed to place sixth while the Schurti / Koinigg entry finished seventh.
Jean-Pierre Jarier and Jean-Pierre Beltoise won in a Matra MS670C with Alfa Romeos second and third.
1974 Imola 1000km
On June 2nd, the new Imola circuit in Italy played host to round four of the 1974 World Sportscar Championship.
Porsche entered two RSR Turbos: R9 for Muller / van Lennep and R5 for Schurti / Koinigg.
Nicknamed ‘The Tank’, R5 was one of Porsche’s works 1973 911 RSRs and had a standard chassis instead of the semi-spaceframe type used by the proper RSR Turbos.
Instead of the usual turbocharged engine, the one fitted to R5 (Type 911/78) had been modified so that the cooling fan lay flat on top of the engine like a Porsche 917. Trialled in an attempt to reduce cylinder head temperatures, it apparently gave a few extra horsepower too. The idea was to test the system at Imola with a view to running it at Le Mans.
During practice, the Schurti / Koinigg ‘Tank’ had a coming together with a Jolly Club 911 and, as a result, only qualified 23rd.
By contrast, Muller and van Lennep started sixth and the solitary Ligier JS2 was twelfth.
More problems for the Schurti / Koinigg ‘Tank’ followed when, on Saturday morning, it stopped after a few laps of unofficial practice with oil pouring from the base of its new fan housing. The Porsche mechanics set about curing the leak although, by the time the other cars lined up for the race, they were still working in the pits.
Schurti eventually got going but, soon after joining the race, he was back in the pits for another 45 minutes to have the turbo rebuilt as one of the fan blades had broken. The turbo eventually expired for good after 133 laps and R5 was not raced again.
In the sister car, van Lennep’s pace had started to slow and when he finally pitted, it was found that half the rubber was missing from the centre of his right rear tyre. The melting track surface had caused the tyres to severely blister.
R9 later started to lose gears and Muller eventually stopped with a box full of neutrals at half distance.
The Imola 1000km was won by Matra with Alfa Romeo second and third.
1974 Le Mans 24 Hours
Off the back of a double DNF in Italy, Porsche entered two RSR Turbos for the Le Mans 24 Hours which was held over June 15th and 16th.
A brand new example (R13) was on hand for Muller / van Lennep and, following the test at Imola, this machine used the new Type 911/78 engine with its flat-mounted fan. The sister car (R12) was entered for Schurti / Koinigg.
Cast aluminium instead of magnesium crankcases were used on both cars in the interest of durability.
Also present in the Group 5 Prototype class at Le Mans were four Matras, two Mirages, a brace of Ligier JS2s and several privateer Porsche 908s. Alfa Romeo were absent.
After some early niggles, Muller qualified the new car seventh. Schurti / Koinigg were sandwiched between the two Ligiers in eleventh.
Like practice, race day was warm and sunny.
The RSR Turbos ran sixth and seventh in the opening stages before being split by one of the Ligiers.
After two hours, the Muller / van Lennep example was up to fifth despite time lost blocked in the pits.
By 8pm, the RSR Turbos were running third and fourth where they remained until 11pm when the Schurti / Koinigg entry retired in a ploom of smoke when its engine blew at full revs down the Mulsanne Straight.
Shortly before midnight, the first and second-placed Matra team were in trouble too. Bob Wollek brought the second place MS670B into the pits with a blown engine and it was out.
The solitary RSR Turbo was thus promoted to second and, by 4am, was seven laps behind the lead Matra. A lengthy stop for a replacement suspension coil cost the Porsche time. Then at 8am, the Matra’s engine started to misfire which took several stops to remedy.
Both cars needed much work over the remainder of the race but ultimately held position. The Porsche had gearbox and steering trouble while the Matra needed a late gearbox rebuild.
At times it looked like either car could win it. However, the MS670C of Henri Pescarolo and Gerard Larrousse eventually took a popular victory by six laps.
1974 Zeltweg 1000km
After its stellar performance at Le Mans, R13 was rested for the Zeltweg 1000km in Austria two weeks later (June 30th). Porsche instead took R9 for Muller / van Lennep and R12 for Koinigg / Schurti.
Alfa Romeo, Matra and Mirage were all present along with a brace of JS2s from Ligier.
The RSR Turbos qualified seventh (Muller / van Lennep) and eighth (Schurti / Koinigg) while the Ligiers started tenth and 13th.
The French cars initially got the jump off the grid but were quickly overhauled by the now superior RSR Turbos.
There was soon drama in the Porsche pits when Koinigg came in ten laps after he had blasted by van Lennep. Koinigg said that the gearbox was not working properly but, when the mechanics checked it, they could find no fault and so he was sent out again. However, R12 didn’t make it out of the pits before the car lost all power. It transpired Koinigg had turned up the boost to pass van Lennep and blown the turbo.
Later, Muller was hampered by a broken throttle linkage which he fixed out on the circuit. R9 then fired back up and went on to claim sixth overall behind two Matras, two Alfas and a Mirage.
Pescarolo and Larrousse made it five wins on the bounce for Matra.
1974 Watkins Glen 6 Hours
Another two-week gap followed and then the teams had to be in the USA for the Watkins Glen 6 Hours on July 13th.
Mirage and Ligier skipped this event while Porsche reduced their effort to a single car for their last three races of the season.
R13 was used at Watkins Glen, Paul Ricard and Brands Hatch with Herbert Muller and Gijs van Lennep taking the wheel on each occasion.
Porsche missed the first day of Watkins Glen practice (Friday) after R13’s tail section and wheels went missing en route from New York to the circuit. When the parts turned up on Saturday, the car was found to have the wrong gear ratios and a faulty distributor.
Both were changed for the race which Muller and van Lennep started fourth behind a brace of Matra MS670Cs and a sole Alfa Romeo. The second Alfa had been severely damaged in practice.
The race took place in sunny conditions and, after two hours, the RSR Turbo was up to third.
It was then promoted to second less than an hour from the end when Mario Andretti’s Alfa Romeo dropped out. Here the Porsche stayed. Muller and van Lennep came home eleven laps behind the winning Matra MS670C of Jean-Pierre Jarier and Jean-Pierre Beltoise.
Alfa Romeo were not seen again in 1974.
1974 Paul Ricard 1000km
In the Paul Ricard 1000km event on August 15th, the Porsche squad had an unusually troubled race. R13 initially qualified eighth, well ahead of the Ligier JS2s in 17th and 18th.
However, van Lennep lost fifth gear in the first hour of the race and then the Porsche would not refuel properly. As the event wore on, R13 lost more gears and eventually crossed the line stuck in second. That it still placed seventh was a miracle.
Matra took another one-two with Mirage third.
1974 Brands Hatch 6 Hours
Porsche did not plan to attend the Kyalami 6 Hours in early November so the Brands Hatch 6 Hours on September 29th would be the last appearance for the RSR Turbo.
With no Alfa Romeos or Ligiers present, the premier class was a little thin: just Porsche, Matra and Mirage.
New Dunlop tyres for the Porsche were thought to be good for a second a lap but the tight and twisty nature of the English circuit meant the RSR Turbo was difficult to keep on boost.
Muller and van Lennep started tenth behind a number of two-litre Group 5 Prototypes which were much better suited to the circuit.
The Porsche drivers steadily rose up the leaderboard and looked set to finish fourth with just 45 minutes to go. However, soon after Herbert Muller went out for his final stint, he went off track when lapping a slower vehicle. The Porsche’s front apron broke off in the process which resulted in a dramatic reduction in downforce.
Muller pitted next time round but a replacement part could not be fitted in time so he was told to finish the race. This was not so easy as, every time he snatched fifth gear, the rear downforce and acceleration lifted the front wheels clean off the track.
R13 eventually finished fifth while Matra took another one-two.
End of the 1974 Season
Thereafter, the RSR Turbos were retired from competition duty.
One week after the race at Brands Hatch, Helmuth Koinigg was killed racing for Surtees in the United States Grand Prix at Watkins Glen.
Although not gunning for the title, Porsche finished third in the 1974 World Sportscar Championship with 68 points. Alfa Romeo were fourth on 65. Matra were clear winners on 140 with Mirage second on 81.
Owing to a lack of manufacturer support, the FIA postponed the introduction of their Group 5 regulations until 1976.
Although they did not officially race in 1975, Porsche continued to develop their turbocharged 911s and also created a new top flight turbocharged Prototype for 1976: the 936.
Text copyright: Supercar Nostalgia
Photo copyright: Porsche - https://www.porsche.com
