BLOWN AMBITIONS
How the mighty Turbo RSR never quite lived up to expectations
“KEEN TO MAKE THIS NEW RACE CAR AS RADICAL AS POSSIBLE…”
You could day it all started with a fuel crisis. Porscheʼs domination of the Can-am series, with the all-conquering 917s driven by the likes of Mark Donohue, Milt Minter and George Follmer, was brought to an end by the SCCAʼS decision to effectively outlaw the mighty turbocharged machine. The Arab-israeli war had resulted in fuel shortages, with a consequent rise in petrol prices, giving the SCCA due cause to make rule changes so as to be seen to be what we might today call ʻpolitically correctʼ.
Of course, we all know the real reason: Porsche had destroyed the opposition and there was every likelihood that nobody else would come out to play if the 917ʼs winning ways were to continue. The SCCA, keen to protect its domestic interests, subtly rewrote the rule book, reducing the fuel capacity of each car thereby making it impossible to run a turbocharged 917 competitively.
In Europe, there was talk of a new FIA Prototype class for 1975, based around ʻsilhouetteʼ production-based machines which bore a closer resemblance to the cars you could buy from the dealer. But the introduction of the new class was delayed until 1976, the class evolving into what became known as Group C, entries for which bore absolutely no relation to any production car.
But, of course, Porsche had already been one step ahead of the game and had set about developing a new production-based racer that could not only compete in the proposed new class but also serve to promote the all-new road-going Porsche 911 Turbo – Type 930.
The race department was keen to make this new race car as radical as possible, exploiting every loophole in the regulations it could find.
The idea of a silhouette formula gave the race engineers a great deal of latitude to create a ground-breaking new car. There was much talk of building an outrageous glassfibrebodied 911, the shell of which would be mounted on a lightweight aluminium tubular chassis. A sort of Can-am 911, if you will, but rear-engined in line with production models. It would have been a winner, of that there can be little doubt.
But Dr Ernst Fuhrmann had other ideas. As head of Porscheʼs race department, he had the ultimate say over what direction this and any other project should take. His reasons were twofold. First, the cost. By embarking on a totally new chassis design from scratch, the budget would have to be very generous indeed. This was a period when Porsche could ill afford to make a major investment in a new race programme as the company had, like so many others at the time, taken quite a hit thanks to the oil crisis.
Second, Fuhrmannʼs preference to base the new car, however loosely, around the production model would, he felt, also help to act as a sales promotion tool for the new 930.
However, because the new car – generally referred to as the Turbo RSR – was conceived to compete in the FIAʼS new Prototype class, the way was open for Porsche to develop the 911 to a level previously unseen.
The biggest departure was in the area of the suspension. Gone were the torsion bars, which had been a feature of every production model from day one, and in their place were coil-over damper units at each corner. These consisted of progressively-wound titanium coils over Bilstein damper units.
At the front, the stock-style Macpherson strut layout was retained, but with spherical joints, as was the semi-trailingarm design at the rear. These rear suspension arms, however, were fabricated from aluminium, hand-formed and welded to machined aluminium uprights. The torsion bar mounting and tubes were also notable by their absence. In total, the Turbo RSRʼS set-up was some 66 pounds lighter than that of its predecessor.
Suspension geometry was heavily revised compared to stock, with the front struts featuring raised spindles to lower the nose of the car – a trick first used on the original nonturbo Carrera RSR prototype back in 1972.
The suspension was also set up to induce anti-squat under acceleration, and anti-dive under severe braking. Today, all these modifications seem relatively simple – after all, you can now buy coil-spring conversions for almost any torsion-bar 911 – but at the time they were groundbreaking.
The bodyshell itself was heavily modified. Although the central ʻtubʼ remained clearly identifiable as that of the 911/930, it was derived from that used on the normallyaspirated Carrera RSR. The rear panelwork was cut away to make way for an aluminium subframe to support the engine and ancillaries. The bodywork was far lighter than stock thanks to the extensive use of glassfibre panels.
Both doors, the front and rear ʻlidsʼ, and the front and rear valances were all lightweight mouldings, while the side and rear windows were Plexiglas. The bulky rear panel surrounding the rear window, and which swept back towards the huge rear wing, featured a forward-facing air-scoop to direct cool air into the engine bay. The first prototype actually featured a separate wing mounted on struts, so that it could quickly and easily be adjusted at the track. Fuhrmann, however, disliked the design.
To his way of thinking, it was important that the overall look of the car reflected that of the production 930, so the rear wing was redesigned to become something of a caricature of the 930ʼs whale-tail spoiler. During a trip to the wind-tunnel in Stuttgart, the team, led by Tony Lapine, tried various ideas to meet Fuhrmannʼs demands. The first comprised a pair of two sail panels that reached back from either side of the rear window to support the wing, with a flat panel that bridged across between them.
This satisfied Fuhrmannʼs wishes but proved to be far from efficient in the wind tunnel, as the design disrupted airflow over the wing itself. The solution was to gently lift the rear edge of the roof and flush-mount the window in a slightly raised position. Note there was a full-width rear apron, the centre section of the rear bodywork being dispensed with to make room for the huge single turbocharger and associated plumbing.
The new wing and rear bodywork became the RSRʼS trademark feature, along with the massively-extended rear wheel-arches necessary to cover the huge centre-lock wheels and tyres. And huge they were! They retained the same 15-inch diameter of the road-going 911ʼs Fuchs wheels, but measured a healthy 11.5ins wide at the front and either 15 or 17 inches at the back, depending on track conditions. As a consequence of the wide wheels and corresponding arches, the Turbo RSR was some two metres wide – some 15.5 inches more than the original narrowbodied 911.
The brakes and steering were the same as those of the
Carrera RSR, with ventilated cross-drilled discs fitted with four-pot calipers. They had proved to be perfectly adequate on the earlier car and there was felt to be no need for change on the Turbo RSR.
The interior, however, came in for some major revision. To begin with, the fuel tank which had previously resided in the front ʻluggageʼ compartment was now relocated to the right side of what would have been the rear passenger seat area. This was to help improve weight distribution in the lefthand drive RSR – and, because it was more centrally located fore and aft, as the fuel level (and hence weight) fell during the course of a race, there would be less of an effect on handling.
Most of the remainder of the interior was taken up with a substantial aluminium rollcage, which added muchneeded rigidity to the lightweight bodyshell. The dashboard was still recognisably ʻ911ʼ in design, but the pedals and gear shift assembly were bespoke.
But what of the engine and transmission? The latter was based on the production 915-series fivespeed transaxle and, despite a stronger sideplate to help keep the ring and pinion together, proved to be the weakest link in the whole car. Simply put, the unit was not quite man enough to withstand the torque generated by the turbocharged flat-six… For most races, a solid ʻspoolʼ was used in place of a differential.
The engine was a new venture for Porsche. Not in terms of the use of turbocharging, but because throughout their participation in the Can-am series, the race department had been free of any form of restrictions regarding engine capacity. That led to a train of thought that went ʻif enough is good, then more has to better ʼ.
But the FIA took a different view, imposing a displacement factor of 1.4 on all turbo- or supercharged engines. The CanAm motors had a displacement of 5.4-litres, and produced a massive 1100bhp. The FIA rules limited engines to 3.0-litres normally-aspirated, or 2143cc blown. If all else was equal, by following the lessons learned from the Can-am programme, that would equate to a power output of 437bhp. There was concern that this wouldnʼt be enough to get the job done, as normally-aspirated 3.0-litre engines were capable of producing around 480bhp.
To fit within the rules, Porsche came up with a 2142cc engine – a flat-six, naturally – that comprised a 66mm crankshaft from the 2.0-litre 911, in conjunction with 83mm Nikasil cylinders and titanium con-rods ʻborrowedʼ from the old 906/Carrera 6. The heads featured 47mm inlet valves and 40.4mm exhausts, the former being of titanium. All valves were sodium-filled, a trick learned during the Can-am days. Compression ratio was a modest 6.5:1 in deference to the KKK turbo. In an effort to save weight, the Turbo RSR engine was based around a magnesium crankcase, rather than the stronger aluminium type then in production.
The engine in its initial form was shown to produce between 400 and 450bhp, depending on boost levels. This was considered promising, but the Achillesʼ heel was heat. All turbocharged engines will tend to run hotter than their normally-aspirated counterparts as the inlet air becomes heated by the exhaust gases flowing through the turbine housing. This not only has a detrimental effect on power, but also, inevitably, on cylinder head temperatures, leading to early failure of the seal between heads and cylinders.
To combat this, Fuhrmannʼs team designed an aluminium intercooler that sat above the rear of the engine, fed by large NACA duct ahead of the rear wing. It was installed on one of the two development cars, which were scheduled to appear
“IF ENOUGH IS GOOD, THEN MORE HAS TO BE BETTER…”
at the Le Mans test day on 23 March 1974.
The test session showed the Turbo RSR to be considerably faster than its predecessor, lapping some 11 seconds quicker than the best time set by a non-turbo Carrera RSR in 1973. In a four-hour race the next day, the two cars drew a lot of attention and undeniably showed promise. But the RSR driven by Koinigg and Schurti broke a rocker arm in the first heat, while the number one car of Gijs van Lennep and Herbert Müller ran out of fuel on the last lap in the first session and then destroyed a turbo in the second.
The team returned to Stuttgart with mixed emotions and immediately began work on preparing the cars for their first championship appearance at Monza in April. The inlet manifold was revised, as was the design of the intercooler. With 450bhp available at 8000rpm, the two cars (chassis number 911 460 9101 R12 as number one team car, and chassis number 911 460 9016 R9 entered as a ʻT car ʼ – for backup) were loaded and driven to Italy.
Driven by van Lennep/müller, the Turbo RSR qualified in 12th position, lapping some seven seconds faster than the first of the Carrera RSRS back in 22nd on the grid. In the race itself, the singleton Turbo RSR finished a creditable fifth overall.
At Spa in May, the same cars and drivers were entered for the 1000km race, qualifying in seventh place on the grid (the ʻTʼ car was ninth). In the race itself, van Lennep/müller finished a worthy third. Things were starting to look up for the Martini-backed team.
At the Nürburgring two weeks later, two cars were entered, the second driven by Schurti/koinigg. Müller/van Lennep qualified in 12th position, just over 3 seconds quicker than their team mates in 14th. In the race, the Turbo RSRS finished in 6th and 7th positions, despite both having been involved in accidents in both practice and the race itself.
At the beginning of June, two Turbo RSRS appeared at Imola, one of which created considerable interest in the pits: it wore a ʻflat-fanʼ cooling arrangement, as opposed to the original vertical fan layout previously used. This differed from the flat-fan system used on earlier race engines, which were gear-driven. On the Turbo RSR, the fans were to be driven by a shaft rotated by a V-belt off the crank pulley.
However, things did not go well for Porsche in Italy, for the flat-fan car (the engine of which was referred to as the ʻPhase 3ʼ design) was delayed by oil leaks, a faulty fan and an ailing turbocharger. Its sister car broke its gearbox and was left stuck in fourth gear. Neither Turbo RSR was classified as finishing the race.
All eyes were now on Le Mans, where the team had high hopes of heading the field against opposition in the form of the screaming Matras and thundering Gulf-mirages. The cars were clocked at a fraction under 190mph on the Mulsanne Straight with the boost wound up to ʻmaximumʼ.
After qualifying, the Martini-liveried RSRS of van Lennep/müller (running the new Phase 3 engine) and Schurti/koinigg (with the vertical fan Phase 2 unit) found themselves in 7th and 11th on the grid, respectively. Matras took four of the top six places, with the remaining two grabbed by a pair of Gulf-mirages.
In pre-event press coverage, the two Porsches were hardly given any ʻinkʼ, all eyes being focused on the Matras and John Wyer-prepped Gulf-fords. Indeed, as the race got underway, the Matras began pulling away from the field, the Gulf-fords struggling to keep pace. And the Porsches? By the second hour, the van Lennep/müller entry was a lap
down on the leaders, their progress having been slowed by their pit space being blocked by a 908 which was undergoing major ʻsurgeryʼ.
As night began to fall, the two Turbo RSRS found themselves in third and fourth places behind the two Matras, but then disaster struck when the number two team car (wearing race number 21) of Schurti/koinigg threw a rod, spewing oil over the hot exhaust system. The back of the car was enveloped in flames, prompting some fancy footwork by the marshals as they sprinted to the rescue.
Holding onto third position, six laps behind the leading Matras, the van Lennep/muller Turbo RSR battled on through the night until the news broke that two of the Matras were out, one being the secondplaced car of Wollek/jassaud/dolhem, which blew up in spectacular fashion. This pushed the Martini Porsche up into second place, which it held until the following morning.
Le Mans is always a war of attrition, and nobody dared take anything for granted – least of all Porsche who were painfully aware of the RSRʼS weaknesses. But van Lennep/müller kept on plugging away, holding off the pursuing Jabouille/migault Matra snapping at their heels in third place, despite its engine beginning to tire in the heat.
And the RSRʼS Achilles heel struck again: van Lennep brought the car into the pits having lost the first three gears! A couple of laps later, it was back in again to investigate a problem with the steering. Müller took the car out and later returned to the pits when he was left with just one gear!
With just 90 minutes to go, the rain came (as it always seems to at Le Mans) but it didnʼt last long. Into the final hour and the leading Matra had a margin of five laps over the Turbo RSR, which now had only third and fourth gears functioning. Luck was on Porscheʼs side, though, and the van Lennep/müller entry managed to hold on to its second place, finishing some 75km behind the winning Matra of Pescarolo/larousse.
The rest of the season brought mixed results for the Turbo RSRS. In July, van Lennep and Müller grabbed another second at Watkins Glen, followed by a sixth at Zeltweg and a fifth at Brands Hatch. At the final round of the championship at Paul Ricard in August, the van Lennep/müller car finished seventh, despite only having one ratio (second, at that) left working in the gearbox.
Porsche finished the season in third place in the championship behind Matra and Gulf-ford. The Turbo RSR had shown promise but was not quite fast enough to keep up with the more radical competitors, nor reliable enough (thanks largely to the gearbox) to outlast them if they happened to run into trouble.
Porsche decided not to continue competing with the Turbo RSR past the 1974 season. The new silhouette formula would not come into play until 1976, meaning that 1975 would have promised more of the same ʻalmost but not quiteʼ situation that bugged the teamʼs efforts in ʼ74. Porsche was even reluctant to sell any Turbo RSRS to privateers for fear of poor results affecting sales of the 911.
So the car which many have come to regard as one of the ultimate 911s, in reality did not have the most illustrious of careers. With just one seasonʼs use, and no outright victories, the Turbo RSR still remains, however, one of the most memorable machines ever to come out of Stuttgartʼs race department.
“PORSCHE WAS EVEN RELUCTANT TO SELL ANY TURBO RSRS…”