Cross compatibility of Porsche’s components have led to some of the most successful and memorable Porsche models in their history. Further development of existing components and the ability to selectively incorporate proven components from competition models into a road car chassis has allowed for purpose-built “parts bin” models like the type 954 SC/RS to come to fruition.
In mid-1981, experimental work was performed to produce a 911SC rally engine with 10.5:1 compression ratio, achieved through specialized forged pistons and six individual throttles, test engine revved to 8k rpms and produced 280bhp at 7,300rpms from the standard 3.0-liter. Porsche sought to gain homologation for Group B rally with the 911SC. FIA Homologation required a 12 month production of a minimum of 200 cars, which the 911SC easily surpassed. A new 911 was slated to be produced for the model year 1984, but a loophole in the FIA’s rulebook allowed a manufacturer to produce 10% of the previous homologation model. This meant that Porsche would only have to produce a run-on “evolution” version of the 911 SC, and would only have to produce a total of 20 cars. With that in mind, Porsche pulled out the stops on the SC/RS.
As a design study, the 911 SC/RS is brilliant. It channels the same raw element and direct lineage to motorsport engineering as the 1974 Carrera RS, and is as impressive on paper as it is in person. Engineers began with the standard Turbo body and incorporated suspension from the Turbo models with the addition to coil “helper” springs to better support the standard torsion bars in anticipation of the abuse of the rally stages. Both the front and rear axles received 18mm anti-roll bars. The exterior panels were constructed from thinner gauge steel and aluminum to shed weight, glass that was 1/3 thinner than the standard production windshield, and plexiglas windows for all the remaining windows. The front and rear bumpers were made from lightweight fiberglass, and the interior was stripped of any superfluous bits that weren’t essential, and the seats were replaced by two 935 Recaro racing seats.
The SC’s 3.0 liter-engine served as the basis for the SC/RS and incorporated racing cylinder heads from the 935, massaged by engineers to a 10.3:1 compression ratio. The street version produced 250 horsepower @ 7,500 184ft-lb torque at 6,500rpm- the highest point of a very flat curve, while the racing tune produced up to 280hp. The brakes were derived from the 917/930, as was the Turbo’s rear wing. The five-speed transaxle was sourced from the 1984 Carrera, albeit with close gear ratios, a ZF 40% limited-slip differential and the clutch from the RSR. A hand-built exhaust system that deleted the heat exchangers was borrowed from the 1974 RS. Overall, the car weighed in at 2,116 lbs with an empty fuel and oil tank, the absolute minimum that was allowed for its under three-liter class. Only six of the SC/RS models had support from the Porsche factory, and only England’s Rothmans cigarette brand had the fiscal fortitude to be competitive on the world stage.
Out of the box from Porsche, the SC/RS should have been an absolute force to be reckoned with. In actual competition, however, the SC/RS struggled to find success as the cars suffered structural and mechanical difficulties throughout the grueling rally stages. Throughout 1984, mechanical issues plagued the SC/RS and lack of support from the factory frustrated the team manager, Charles Reynolds, and team owner, David Richards, enough to write a memo to Rothmans public relations boss, Sean Roberts, detailing their troubles.
“It was always our intention that Porsche would supply service to the team, however, as well intentioned as their efforts have been, it would seem that, as a result of either lack of time, direction or commitment to our programme, this has never materialized.”
This prefaced the beginning of the Prodrive re-engineering program to strengthen and improve the cars to the point that they would be able to withstand the rigors of such punishing terrain. In the memorandum, Richards outlines some of the issues the team was facing. “The Middle East car, after only three events, has shown signs of cracking and bending of the body. It is now obvious that the cars used for rough road events need extensive strengthening.”
Richards’ crew completely disassembled each car and rebuilt them to the standards that they had used in the past to claim victory in previous World Rally Championships. Prodrive’s Rally competition preparation added an integral roll cage, aluminum doors and front deck lid, Kevlar engine cover and wing, 14-kilogram fire extinguishing system, Halda navigation computer, and additional lights. The A pillars and bulkheads were strengthened to combat the flexing body, and the alloy trading arms were laminated with Kevlar to stop rock damage.
Bumpy stages stressed the torsion bar suspension and made the SC/RS difficult to drive, which prompted Jurgen Barth to push for-and in April 1984 successfully convince the FIA to homologate- for coil-over Bilstein suspension. Not only did the addition of coil-over suspension make the car more compliant and controlled over rough stages, it allowed the team to address the necessary suspension stiffness that they required.
Time and time again, the gearbox proved to be the weak link in the SC/RS’s armor. Telexes from Prodrive consistently cite the failures of the gearboxes syncromesh and shift forks, forcing the team to replace them with spare gearboxes between stages and consistently shipping them back to Porsche to have them rebuilt in time for the next races. In some instances, the gearbox failures were the pivotal factor between success and failure for the Rothmans team, but throughout the seasons it was most certainly a monumental cost and source of frustration.
With each successive rally, the Prodrive team was able to identify and remedy the weak points in the Rothmans SC/RS team cars and improve on Weissach’s engineering- making it a more resilient and competitive rally car than it ever could have been straight from the factory. Between 1985 and 1987, failures became more infrequent and Rothmans SC/RS Chassis 008 saw consistent finishes in each subsequent race. With five outright wins out of 13 rallies between 1984 and 1987, chassis 110-008 became the most successful of the SC/RS examples that were campaigned through consistent redevelopment by Prodrive.