In 1970 new rules allowed the wheel arches of the 911 to be extended (flared) a further 2 inches from standard to accommodate wider wheels. The engine capacity was also increased to 2195cc by increasing the bore to 84 mm. Porsche could now enlarge the cubic capacity of the engine by bore increase only, as per regulations, enabling them to run at the next class limit of 2,5 litres – an objective accomplished in several stages.
At the first stage, the capacity of the engine was increased to 2247cc, an increase in bore of just 1 mm to 85 mm. At the same time the factory made use of “Biral” cylinders which consisted of cast-iron cylinders with alloy fins bonded on. Twin ignition had now been homologated (with normal coils and contact breakers) and this was part of the engine tune, together with polished and crack tested connecting rods.
The compression ratio of the 2247cc S-model was 10.3:1. As before, standard valves were used (46mm inlet and 40mm exhaust). Bosch twin row, six-plunger pump (mechanical) fuel injection was now used, the pump of which was modified with a space cam to match the Carrera 6 racing cams which were installed. Tuned induction pipes without an air filter were also used. The racing engine for group 4 could be ordered with Weber IDA carburettors with 42 mm diameter choke tubes – curiously the factory claiming a power output of 230 hp for both units. The standard crankshaft and bearings were also used, measuring 66mm. Thirty of these engines were built, the factory designating them “Type 911/20.”
For the 20 cars built to take these engines, the roofs, parts of the floor pans and the scuttles were made in thinner gauge steel than in the road cars. Cars retained and ran by the factory enjoyed thinner steel in their doors too. In March 1971, the cylinder bores were opened up even more to 87,5 mm and this increased the capacity to 2381cc. The output of this engine was 250 hp, both with fuel injection and with carburettors, achieving its peak at 7800 rpm.
These racing versions of the 911, which were known internally as S/T, had their seat slide supports and the heater ducts removed, as were the seatbelt anchorage points, the glove box lid and the ashtray.
Missing also were the engine cover and front cover locks, these being replaced by rubber fasteners. Also taken out were the sun visor, front torsion bar protectors, fog light recess covers and the rear torsion bar covers. There was no soundproofing or under seal, and even the amount of paint used was kept to a minimum.
Further options from the factory to lose weight included a plastic front cover as well as front and rear bumpers made of the same material, as well as aluminium skinned doors with steel frames of 0,75mm thickness. Plexi-glass was available to replace all glass except for the wind-screen which, however, could be ordered with even thinner glass. A transverse bar was fitted in the front compartment between the front struts to aid stiffness in this area, and fuel tanks of 17.6 or 24.2 gallons were available. The whole racing package was finished off with Recaro racing seats.
Chassis Number 19300644 was manufactured as a normal S by the factory and duly sent to the Werks Porsche Competition Department who converted T, E, and S specification cars into S/T Specification straight from the production line. The car was sold to Kent Frohde, resplendent in Conda Green, on the 22th September 1971. The engine- an original 2 Litre – was tuned to 242bhp. According to Kent Frohde, this was the strongest 2 litre engine that Porsche had tuned at the time.
The car was raced in Swedish racing series at the beginning of the 1970s until it was retired, and the last time it was road worthy was 1976. During 1970 to 1976 it follo§wed the evolution of race cars and was upgraded to meet the competition.
Chassis 119300644 comes complete with a large history file, containing a letter from Kent Frohde confirming its authenticity. The car has been used by its current owner on a large number of European events and rallies where it has performed well. It also benefits from a recent and documented engine rebuild.
This is the ultimate of the ultimate 911, one of the rarest and most sought after 911s in the world and surely worthy of a place in any Porsche museum or at any significant worldwide motoring event. Rarely do S/Ts change hand on the open market.