Guide: Porsche 911 3.0 Turbo Carrera RSR (934)
BACKGROUND
For the 1976 season, new rules came into effect for GT and Sports Prototype racing cars.
At the top of the tree, Group 6 was for out-and-out Prototypes and had no minimum production requirement.
Moving down the order, Groups 4 and 5 were open to production-based GT cars once 400 road-going base cars had been produced within a 24 month timeframe.
To qualify for Group 4 and 5, Porsche created the turbocharged 930 road car (the 911 Turbo) 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, its arrival was postponed for a year owing to a lack of manufacturer support.
Group 5 catered for more highly modified production-based 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 – essentially a Silhouette formula.
By contrast, Group 4 cars were more closely derived from the homologated base car: wider wheels and tyres, lightly tuned engines, firmed-up suspension, superior brakes and simplified interiors.
The new 400 cars in 24 months rule for 1976 superseded the outgoing Group 4 requirement of 500 base cars in 12 months. Famously, in a similar vein to the turbocharged 930, for 1973 Porsche had created the 911 2.7 Carrera RS homologation special which spawned the RSR racing variants which went on to utterly dominate Group 4 GT racing from 1973 through 1975.
Production of the new 930 base car started in February 1975 and the 400 units required by Group 4 had been produced by the end of 1975. Homologation for Group 4 and Group 5 was rubber stamped on January 2nd 1976.
In Group 5, the Martini-backed factory team would race the 935 in 1976, this model having been reserved strictly for works use. By contrast, customers were supplied with the Group 4 934, also variously known as the 911 Turbo Carrera RSR.
The first 934 prototype was completed in September 1975, soon after the FIA had provided final clarification of maximum permitted size for wheel rims and fender extensions. Thereafter followed an intensive test programme between Weissach, the Nurburgring and Paul Ricard over the winter of 1975-1976.
CHASSIS
Starting with a 930 bodyshell, Porsche stiffened the front end by way of a strut and cross brace. Also housed under the front lid was a 120-litre fuel tank with exposed filler cap, the fire system and, to optimise weight distribution, the oil tank for the dry-sump lubrication system. In the cockpit, Porsche added a beefy aluminium rollcage.
As per Group 4 regulations, the 934 retained the 930’s suspension layout which comprised MacPherson struts with lower wishbones, longitudinal torsion bars and anti-dive geometry up front and semi-trailing arms with anti-squat out back. Bilstein shocks were fitted all round and along with an anti-roll bar at either end.
To enable customisation for any given circuit, the 934’s ride height and anti-roll bars were made fully adjustable and everything was suitably firmed up to include extensive use of solid instead of rubber bushes.
Reinforced axle guides were fitted at the rear.
Instead of the solid 282.5mm and 290mm discs fitted to the front / rear of the 930, the 934 imported a 917-style arrangement with 355mm diameter drilled and vented discs all around along with lightweight finned four-piston calipers and thicker pads.
Brake bias was adjustable and a modified pedal block allowed for quick installation.
A custom lightweight handbrake assembly not suitable for road use was also fitted.
The 934’s BBS wheels were increased from a 15 to 16-inch diameter and dramatically widened: up from 7 to 10.5-inches at the front and from 8 to 12.5-inches at the rear. They were switched from a conventional five-bolt to centre lock arrangement and mounted reinforced wheel hubs.
ENGINE / TRANSMISSION
In the engine bay was a new Type 930/75 motor which as usual employed dry-sump lubrication, single overhead camshafts and two valves per cylinder. It used the standard 930 engine casing, crankshaft, connecting rods, cylinder heads and 6.5:1 compression ratio. Similarly, displacement was unchanged at 2993cc thanks to a bore and stroke of 95mm and 70.4mm respectively.
Like most of the suspension, the 934 engine and transmission were mounted on solid as opposed to rubber bushes.
Enhancements added to the Type 930/75 engine included larger intake and exhaust ports, uprated pistons, superior camshaft timing, a horizontal instead of vertical cooling fan wheel and a completely new un-silenced exhaust system. The electronic Bosch K-Jetronic fuel-injection system was adjusted to mix precisely the right amount of compressed air with fuel.
The 934 also received a bigger KKK K36 turbo with 917/30 bypass valve, the boost pressure of which was cranked from 0.8 on the 930 to 1.3 bar. The air that passed between the turbo to the induction system was cooled by a complex water system. There was also an intricate twin Behr air-to-air intercooler arrangement that enabled the engine to run more efficiently and reliably.
As a consequence of these upgrades, the power output went from 260bhp at 5500rpm to 480bhp at 7000rpm. There were also considerable torque gains with 434lb-ft now on tap at 5400rpm compared to 253lb-ft at 4000rpm for the 930 road car.
To handle all the extra power and torque, Porsche installed a new reinforced Type 930/25 four-speed gearbox with additional oil pump and oil cooler. A Fichtel & Sachs racing clutch with torsion damping and sintered lining was also installed along with an 80% locking limited-slip differential.
Three alternative ratios per gear were offered.
BODYWORK
To further optimise weight distribution, the 934 came with several fibreglass instead of steel panels. The front lid, doors and engine cover were all switched for this lightweight material while the 934’s custom front spoiler assembly and enormous wheelarch extensions (the latter pop riveted in place) were also fashioned from GRP.
Cut into the front spoiler were five enormous air intakes. The largest of these was housed in the centre and fed the oil cooler. Located off to the sides were slim brake cooling ducts, outboard of which were intakes for the Behr intercoolers.
To further reduce weight, the 934 came with lightened side and rear glass, no sill covers and simplified exterior mirrors.
The front and rear lids were held in place with quick-release pin fasteners.
INTERIOR
Inside, although Porsche retained the standard 930’s door trim panels complete with electric window system, the rest of the cockpit was comprehensively gutted.
The dash was imported from the regular 930, but trimmed with just a thin covering of anti-glare fabric as opposed to leather.
Typically, two of the usual five gauges were blanked off; most cars came with a standard 8000rpm rev counter located directly behind the new three-spoke steering wheel while off to the left was the familiar combined oil pressure / oil temperature read out and on the far right was a turbo boost gauge.
Located to the right of the dash was a toggle to adjust turbo boost. Underneath this was a simplified ventilation system fascia alongside which were further read outs for fuel pump main pressure and bypass fuel pressure.
Two racing seats trimmed in fire retardant fabric were fitted along with competition harnesses and the aforementioned aluminium rollcage.
OPTIONS
Customers could order there 934 with a choice of gear ratios, all manner of spare parts and a lightweight Glaverbel front screen.
WEIGHT / PERFORMANCE
Because the FIA operated a 1.4 swept volume equivalency for turbocharged engines, the 934’s cubic capacity of 2993 meant it qualified for the 4 to 4.5-litre class which had a minimum weight limit of 1120kg.
While the 930 weighed in at 1195kg, it had been homologated at just 1060kg which enabled Porsche to strategically position 60kg of ballast to bring it back up to the minimum weight.
Depending on gear ratios, a top speed of 180mph was attainable. Similarly, 0-62mph could be achieved in just 3.8 seconds.
UPDATES
At the Silverstone 6 Hour World Sportscar Championship race which took place in early May of 1976, one of the 934s campaigned by Egon Evertz (chassis 9306700155) appeared with the wheels, lightweight bumpers, wider single piece fenders (vented at the rear) and bi-plane rear spoiler from the 935. This kit of parts was subsequently offered to other 934 customers and enabled them to run in the lightly contested Group 5 category.
For 1977, a Type 930/73 engine with mechanical Kugelfischer fuel-injection (as opposed to electronic Bosch K-Jetronic) along with a bigger KKK K36 turbo was made available having been introduced for the new 934/5. Peak output of these motors went from 480bhp to 530bhp at an unchanged 7000rpm while the torque rating was unaffected.
END OF PRODUCTION
Porsche 31 examples of the 934-type 911 Turbo Carrera RSR in 1976.
The first 30 cars were completed with consecutive chassis numbers: 9306700151 to 0180.
The 31st and final example built was on chassis 9306700540.
All 31 cars were left-hand drive.
A batch of ten further uprated cars dubbed 934/5 (covered separately) were built up in 1977 with 930770 prefix VINs. These cars, all of which headed for the IMSA series across the Atlantic, came with 935 wheels, bumpers, fenders and spoilers plus the aforementioned Type 930/73 540bhp Flat 6 engine with mechanical rather than electronic fuel-injection.
COMPETITION HISTORY
1976 saw the 934 dominate all of the championships it contested.
In the World Sportscar Championship, 934s won six out of seven races. The Egon Evertz squad took victory twice (at the Mugello 6 Hours with Leo Kinnunen / Egon Evertz and the Silverstone 6 Hours with Lella Lombardi / Heinz Martin) while the Jolly Club, Max Moritz, GVEA and Kremer Racing teams all took a single win apiece.
Giorgio Schon, Luigi Tomassi and Giuseppe Bianco won the Vallelunga 6 Hours for Jolly Club, Helmut Kelleners, Reinhardt Stenzel and Derek Bell won the Nurburgring 1000km for Max Moritz, Claude Haldi and Peter Zbinden won the Zeltweg 6 Hours for GVEA and Jurgen Barth, Reinhold Joest and Bob Wollek won the Dijon 6 Hours for Kremer.
Thanks to five wins in the seven race European GT Championship (at the Nurburgring, Zeltweg, Norisring, Monza and Hockenheim), Toine Hezemans was crowned the last European GT Champion with a series of peerless drives for Georg Loos.
In the Deutsche Rennsport Meisterschaft (DRM), the 934 won all but one Division 1 class race. Bob Wollek (driving for Kremer) and Toine Hezemans (driving for Georg Loos) took three wins apiece (Mainz-Finthen, Norisring, Hockenheim and Hockenheim, Diepholz, Nurburgring respectively). Hezemans’ team-mate Tim Schenken also took a brace of wins (at Hockenheim and the Nurburgring) and Helmut Kelleners took a solitary win for Max Moritz (at the Nurburgring).
Wollek was the best placed Division 1 contender but DRM championship honours went to Division 2 Zakspeed Ford driver, Hans Heyer.
At the Le Mans 24 Hours (which for 1976 was held independently of any larger championship), the 934 Gelo Racing Team 934 of Toine Hezemans and Tim Schenked finished 16th overall and second in the GT class behind the older 3.0 Carrera RSR of privateer Andre Gahinet which he shared with Michel Ouviere and Jean-Yves Gadal.
Across the Atlantic, in a closely fought campaign Vasek Polak driver George Follmer was crowned the 1976 Trans-Am champion thanks to two wins from eight events (at Nelson Ledges and Trois-Rivieres). Follmer’s team-mate Hurley Haywood also collected a win (at Pocono).
Unfortunately though, the 934 was not permitted to run in the 1976 IMSA series on account of its turbocharged engine.
Beyond 1976, the Porsche 934 retained its status as the best Group 4 GT car around well into the 1980s and went on to achieve massive success in practically every major championship contested.
Text copyright: Supercar Nostalgia
Photo copyright: Porsche - https://www.porsche.com
