Paul Davies recounts the story of the first customer turbo race car, the #Porsche-934
. The Porsche 934 blended the RSR Carreras of the early seventies with pressurised induction to cook up the first customer turbocharged racer.
Can you have a fusion automobile as well as fusion cooking? Take a well-proven chassis, and engine, mix with all you’ve learnt about turbocharging from sports car racing in the United States with the 917, and serve up as one of the most successful customer competition cars to come from Porsche. Only 31 examples of the Porsche 934, officially known as the Carrera RSR Turbo (or simply Turbo RSR), were manufactured ready for the 1976 season, but they dominated their category way into the following decade.
There’s always been a Porsche policy of encouraging the customer to go racing, or rallying if comes to it. Competition improves the breed, and it’s often a fast-track means to develop a new model. More importantly, however, was the Stuttgart family ethos that if a customer went racing, successfully, they became a loyal customer. Give the guy the right tools, help him a bit along the way – and he’ll come back time and time again.
Back in the days of the four-cylinder 356, Spyders and the 904, and later with the Carrera 6, it was private entrants around the world who snaffled most of the silverware and helped create the Porsche legend. A goodly number of the 43 Porsche 917s manufactured ended up with driver-owners, or private teams, receiving varying amounts of factory support; both of the 917 Le Mans wins of 1970 and ’71 went to ‘private’ concerns.
There’s also been a further thread running through Porsche’s motor sport involvement, one that continues to the present day. Except at the very top level, the customer competition car should be based upon a production model. Which excludes the 917 and also the most successful of all competition Porsches, the 956/962 of the 1980s, but think of the hordes who raced and rallied the 356 in all its forms and the many #911
variants of the sixties. By the early 1970s they were looking for a new car to run.
The answer came in 1973 with the introduction of the Carrera RS. A total of 1580 of the 2.7-litre (2687cc) #Porsche-911
coupé were manufactured in both lightweight Sport (M471 option) and plush Touring (M472) versions, and a large number ended up in motor sport of one sort or another. After all, straight from the factory it had most of the right bits that in those days made a club, or national status, race or rally winner. It was the flag-waving 911 that got people queuing for the more ‘basic’ 2.4-litre model of the day.
But Porsche knew their production racer would not be quite good enough for the serious private entrant. Of that production run, just 49 cars (preceded by eight prototypes) were selected for extra-special treatment before they left the factory. With a further lightened and wider bodyshell, a capacity increase to 2806cc with twin-plug ignition, the addition of 917 brakes, uprated suspension with coil springs supplementing torsion bars, and a stripped-out interior with a roll cage, the Carrera 2.8 RSR (M491) was the car for the serious customer racer.
The Porsche 911 was considered a special grand touring car, and back in 1973 you had to make 500 in a year to qualify for entry into the Group 4 category. Further modifications could be made as an ‘evolution’ of the original car. In 1973 the Brumos team RSR ran as a prototype with a full 3.0-litre engine at the Daytona 24 Hours and it won; later in the year a similar Martini Racing car was outright winner of the Targa Florio, and took fourth overall at Le Mans.
In fact the 2.8-litre engine was a bit of an oddball. The capacity, achieved by increasing the bore of the production Carrera 2.7 RS unit from 90mm to 92mm, was right on the physical edge, and proving unreliable. At that capacity it was also way short of the 3.0-litre international class limit. The obvious double solution was to move to a full three litres (2993cc) utilising an aluminium (instead of magnesium) crankcase, and the same 95mm bore that would later form the basis of the upcoming 930 Turbo road car.
By 1974 the Carrera 3.0 RS had become a ‘production’ customer race car. A grand total of 109 were produced, of which about half were built as RSR versions to very much the same competition specification as the previous 2.8-litre. In addition 15 special cars (outwardly RS but with 3.0 RSR engines) were supplied to compete in the International Race of Champions (IROC) series in the USA.
Both 1974 and 1975 were years for customer cars. In these two seasons private teams dominated on both sides of the Atlantic, with Peter Gregg winning both the Trans Am and IMSA GT series in the USA two years running, and the Kremer and Loos teams sharing John Fitzpatrick’s European GT Championship.
Whilst customers worldwide were winning with the 3.0 RSR, Porsche was otherwise occupied, particularly with trying to win the East African Safari Rally (they came second) and also working to bring a new customer car to the starting grid. That car would be the Carrera RSR Turbo of 1976, the Porsche Type 934. The ‘93’ number signified the car was based on the production 911 (930) Turbo – first shown in 1973 but not to go on sale until 1975 – and the final digit that it was homologated into Group 4.
Only, the recipe for the new car required a certain amount of tasting before it was ready for the table. Following success racing in the Can-Am series in the USA, Porsche had got the turbo bug big. At the peak of development the twinturbo engine of the 917/30 was giving in excess of 1000bhp, and it was logical the company should apply the same technology to both mainstream production (the 911 Turbo) and competition. The introduction of the (short-lived) BMW 2002 Turbo to the European market was an additional incentive to match their big rivals.
Several prototype 911 Turbo road cars were produced (first with a 2.7-litre engine) and to test the configuration to the limit Porsche built four prototype race cars based on the Carrera 3.0 RSR but with a turbocharger. International regulations demanded pressurised induction engines should have a coefficient of 1.4, so to duck under the three-litre class limit the capacity was 2142cc. Even so, with single KKK blower, mechanical injection, twin plugs per cylinder, and an air-to-air intercooler between the turbo and the plenum chamber, the output was upwards of 500bhp.
The rest of the specification was similar to the Carrera RSR, but with lightweight and wider body, and the addition of a large rear spoiler. The torsion bar suspension was deleted entirely in favour of coil springs at both front and rear. Factory Turbo RSRs raced in Martini colours during 1974 and proved relatively reliable, although they could not match the speed of the Matras and Mirages of the time. Second places at Watkins Glen and Le Mans were the highlights.
At the end of the season, Porsche was happy with these ‘turbo-trials’ and announced it would take a break in 1975 and leave things to the Carrera 3.0 RSR privateers. Meanwhile, they readied the 934.
Whereas the small-capacity Turbo RSR was, and looked, very much an out and out racer, the limits of Group 4 (500 of the base 911 Turbo had to be produced to qualify, but no problem there) demanded the 934 be a degree or two more sober. Visually, the 50mm plastic wheel arch extensions were the giveaway, along with the deeper front apron that held a big central oil cooler and twin water radiators – more on these later.
Structurally the body was very much like the stock 911 Turbo, complete with impact front bumpers. Obviously there was a roll cage (alloy in-period, but not permissible now) and all the usual motor sport essentials. The interior was devoid of passenger seating and carpets, but it was not necessary for Porsche to resort to lightweight panels and thin glass to achieve the category minimum weight of 1120kg. In fact, the electric operation of the driver and passenger door windows was retained!
Running gear generally followed previous RSR models, with the torsion bars retained but coil spring-over damper/strut units added to do most of the work. A major change at the rear was the use of short, cast aluminium, trailing arms pivoting on extended fabricated mounts on the rear crossmember, designed to reduce camber change. Solid bushes (nylon or uni-ball) replaced rubber where possible. The wheels were centre-lock, split-rim, 16in diameter BBS alloys of 10.5ins front and 12.5ins rear widths.
The brakes were what tend to be, when used on the 911 Turbo, referred to as ‘917’ but that is somewhat of an understatement. Yes, they were as developed for Porsche’s Le Mans winner of 1970 and 1971, but the vented and crossdrilled discs of the 934 were 304mm diameter at the front and 309mm at the rear, and the alloy four-piston calipers heavily finned to improve cooling and extra-wide to allow endurance pads that were some 25mm thick. There was also a balance bar to allow adjustment of braking distribution front to rear.
The engine was (as it had to be) based on the 911 Turbo, and the famed #Porsche-930
aluminium crankcase that would remain in use in competition Porsches in one form or another right through to the Carrera GT3 RS of 2012. Unlike the Turbo RSR prototype of 1974, the capacity stayed at 2993cc, meaning that when the FIA co-efficient of 1.4 was applied the turbo engine had a calculated swept volume of 4190cc.
In detail the engine was in fact a fusion (again!) of the previous 3.0 RSR, the production 911 Turbo, and the small capacity unit of the RSR Turbo. The cooling fan was horizontal and centrally placed on top of the engine, driven by a belt and shaft just like later versions of the earlier race car – if you see what I mean. Valve sizes (two per combustion chamber) were the same as the naturallyaspirated RSR, but the porting was enlarged. There was one plug per chamber, as the road car, whilst compression was a lowly 6.5:1 to allow for the considerable ratio hike with pressurised induction.
The innovation for the customer racer was the addition of the single exhaust-driven #KKK
compressor. Like the 2.14-litre RSR, this was mounted centrally low within the rear body panel – unlike the 911 Turbo which had its turbo unit positioned bottom-left. The other new move was the introduction of water to cool the air between the turbo and the inlet manifold. With the earlier racer Porsche had demonstrated that passing the forced air through an intercooler before it mixed with fuel in the inlet greatly increased horsepower. With the new car the company sought the most efficient means.
The intercooler of the RSR Turbo was a simple air-to-air radiator positioned above the engine in the rear bodywork, but for the 934 Porsche mounted two small radiators within the front bumper corners (where you’d find the oil cooler on most production 911) and circulated water, by means of a pump driven by belt off the front of the right-hand camshaft, from them to a pair of alloy intercoolers positioned above each cylinder bank. The system proved effective, and the extra weight was lost within the generous minimum weight inflicted by the regulations – just like the electric windows.
In a further nod towards the production 911 Turbo on which the 934 was based, Porsche fitted Bosch K-Jetronic injection and not the purely mechanical system used on previous racing engines. The transmission was an uprated version of the four-speed Type 915 gearbox of the 911 Turbo, with the addition of a small oil cooler mounted in the rear spoiler.
The result of all this was a tough and powerful race car (albeit, by all accounts, somewhat of a handful to drive on account of massive turbo-lag) that looked little different from the 911 Turbo sitting in the showroom. Early race engines developed 485bhp, but this soon grew to in excess of 500bhp.
The 934 ruled Group 4 from 1976 until the early 1980s. In the USA major teams such as Brumos, Vasek Polak and Dick Barbour dominated with drivers of the calibre of Al Holbert, Hurley Haywood, George Follmer and Peter Gregg. In Europe it was Kremer, Max Moritz and Loos, with Bob Wollek, Tim Schenken, Rolf Stommelen and Toine Hezemens who continually took honours. Go to the excellent Racing Sports Cars site (see contacts) for a most comprehensive list! In the USA, the IMSA organisation announced it would not allow turbochargers in its Camel GT series, so Vasek Polak took his cars to the rival SCCA’s Trans-Am competition. Follmer won this in 1976 and Haywood was runner up. Then IMSA did a mind-change and allowed the cars to run in Camel GT. Porsche responded by producing an extra 10 cars – popularly known as 934.5 – with wider rear bodywork for 15in-wide wheels and an enlarged rear wing for 1977, but IMSA banned it before the first race!
Back in the Trans Am series (this is complicated) the 943.5 won six out of eight races, but failed to take the title because of a protest from a (regular) 934 driver! Actually that’s not the end of things. As in all things Porsche there has to be a footnote. The Carrera RSR Turbo was a Group 4 car, and so to compete in Group 5 with a chance of outright victory on major events #Porsche
produced the #Porsche-935
, which by #1979
was to win Le Mans outright. However, that’s another recipe for later.
The 934.5 was built to give Porsche the advantage in the USA, being a Group 4 934 with big rear wing and larger rear wheels. Peter Gregg is seen here at Watkins Glen, 1977.
2.1-litre Turbo RSR was built to test the concept of the pressurised 911 racer, and run in Martini colours in 1974. Here is Gjis van Lennep at the Nürburgring The turbo 934 was, in effect, a development of the normally-aspirated 3.0 Carrera RSR which won the 1973 Targa Florio (below).
Prill Porsche Classics:
Racing Sports Cars:
Jens Torner: Porsche
Nick Faure: Le Mans driver
PORSCHE 934 CARRERA RSR TURBO CHASSIS NUMBER 930 670 0153
Our featured car was the 17th of the run of 31 #Porsche-934
s manufactured early in 1976, and sold to Belgian driver and team owner Jean Blaton – who raced under the pseudonym ‘Beurlys’. After race preparation by Kremer (including a repaint from yellow to white) it was delivered to the Le Mans 24 Hours to be driven by Nick Faure (GB), John Goss (AUS) and ‘Beurlys’.The car was retired due to a number of turbo failures, but restarted to finish the race, although it was officially ‘not classified’. Turbo technology was new, and it is likely the drivers were unaware the engine had to be idled to reduce turbo temperature whenever it came into the pits.
After Le Mans, Blaton sold the car to Jean-Pierre Gabon and it contested the following two Le Mans but failed to finish on either occasion. Results included wins in the 1978 Grand Prix of Zolder and the Spa 600kms (Willy Braillard). The car was sold in 1982 to the Vermuelen brothers, who subsequently sold it to long-time owner Walter Pauwels. It was repainted to its original yellow prior to sale by auctioneers Coys in 2014 and is now in the custody of specialist Andy Prill for the new owner.
“The innovation for the customer race car was the addition of a single KKK compressor…”
The KKK turbo is mounted low and central behind the rear bumper panel, oil catch tank is to the right. The engine had to be idled for one minute before switch off to stop the bearings overheating.
Rear suspension has coilover damper on screw platform and torsion bar with adjustable spring plate. Adjustable anti-roll bar uses uni-ball joint and nylon bushing.
A small gearbox oil cooler is fixed behind the grille in the rear spoiler. Engine oil and twin intercooler water coolers are mounted within the front bumper.
Horizontal cooling fan (as 917 and Turbo RSR of 1974) is more efficient than stock 930 Turbo vertical configuration. Small tank (top RH) is header for turbo intercooler water. Watercooled alloy intercooler is mounted above each cylinder bank and helped to reduce induction temperature from 150 deg C to 50 deg C.
Turbo wastegate hides lower left. Normal boost pressure was 1.3 bar (18.5psi) which gave 485bhp, but greater pressure could deliver figures up to 580bhp.
NICK FAURE REMEMBERS HIS 1976 LE MANS WITH ‘0153’:
‘It was brand-new from the factory when the Belgian team turned up with it at the #1976
Le Mans. These cars were a completely unknown quantity on the track and it was early development days for turbos in racing. The car arrived at the race in bare white from Kremer and I painted on the team colours in the pits.
We had to race the car in production weight with electric windows and a lead weight bolted to the passenger floor. Crazy! What neither Porsche, or Kremer, realised at the time was that when the car came into the pits the turbo was still turning at colossal speed and without being allowed to cool down it blew apart.
When it got to changing the fifth new turbo during the race, Jean said that he’d had enough. So he parked it up until the final laps and then just drove it slowly to the finish to complete the race, albeit many laps down.
In the middle of the night when we were changing something like the third turbo a ‘tired and emotional’ Duncan Hamilton turned up in our pit with his Aussie friend Jumbo Goddard, offering his advice. He explained that Jumbo had a turbocharged XK120 so he might be able to give us some help!
Of course in those early days it was a single large turbo with huge lag, but at La Sarthe that did not matter so much as it was a very flowing circuit with only two slow corners at Mulsanne and Arnage. I was offered the car for £10,000 after the race but sadly that was more money than I could have raised.’ Nick Faure.
Well braced front compartment includes a 120-litre fuel tank and a 22-litre oil tank, both with fillers accessed through flaps in the lid.
Bilstein front strut has coil spring, but Group 4 regulations demand stock torsion bar is retained. The brakes are 917 ‘endurance’ specification, with superthick pads.
Standard wheel fitment for the Group 4 car was the split-rim #BBS
alloy with centre-lock fastening. Note the rear wheels have the tyres bolted to the rims to prevent movement.
The 934 proved to be a popular – and successful – entrant in sports car racing long after its intended lifespan. How many can you count in this photo!
“Structurally, the body was very much like the stock #Porsche-911-Turbo-930
, complete with impact bumpers…”
CARRERA RS/RSR ENGINE DEVELOPMENT
Engine Bore/Stroke Capacity Induction Power (bhp) Torque (lb ft)
90mm x 70.4mm 2687cc Mechanical inj 210 @ 6300rpm 188 @ 5100rpm
* 92mm x 70.4mm 2806cc Mechanical inj 300 @ 8000rpm 217 @ 6500rpm
95mm x 70.4mm 2993cc Mechanical inj 230 @ 6200rpm 202 @ 5000rpm
* 95mm x 70.4mm 2993cc #Bosch
Mechanical inj 330 @ 8000rpm 230 @ 6500rpm
* 83mm x 66.0mm 2142cc Turbo/mech inj 480 @ 7600rpm 340 @ 5400rpm
95mm x 70.4mm 2993cc Turbo/ #Bosch-Jetronic
inj 500 @ 7000rpm 430 @ 5400rpm
(* twin spark ignition)
RUMBLE IN THE JUNGLE
The two works 911s entered for the #1978
East African Safari Rally were billed as SCs and presented in red, white and blue Martini colours. The car (14) crewed by locals Vic Preston Jnr and John Lyall finished 2nd overall, with Bjorn Waldegård and Hans Thorszelius (5) placing 4th. Painted in white and red Esso Eminence livery, the Alméras SC saw action at international level in the #1982
Tour de Corse, while the Prodrive cars emerged as Rothmans SCRSs for Henry Toivonen to take five wins in the #1984
European Rally Championship.