2.7 Carrera: the forgotten icon
The 2.7 RS appeared for less than one model year, but the 911/83 engine lived on for two more…
Why the 2.7Rs-engined Carrera MFI is a secret collectors’ gem
When Hans Mezger made the first drawings for Porsche’s flat six, the two-litre capacity was chosen, as this was considered to be the right size for Porsche buyers. However, sufficient margin was built into the design to accommodate later capacity increases: in 1969 it rose briefly to 2.2 litres before it reached 2.4 in 1971 and 2.7 (in standard production) in 1974. In fact, before the end of the decade it would reach 3.3 litres for the Turbo engine, and Ferry Porsche was prompted to remark that had he known in 1963 how much more capacity would be possible, he would have started off with a smaller, lighter unit in the first place: “Now I’m glad I didn’t!” he told his biographer John Bentley.
Initial discussions in 1959 were on a possible pushrod flat six for the 356’s successor, but when it was realised that this design potentially offered little more refinement than the 356’s flat four, and even less margin for tuning in competition applications, it was abandoned in favour of the famous 901 engine: by
1963 standards this was a remarkably advanced design with overhead cams, seven main bearings and a dry sump. Hans Mezger describes in his autobiography how he and fellow 901 engineer Ferdinand Piëch had to fend off criticism within Porsche that their design was too expensive, pointing out that it had at least a ten-year life and was made so that camshafts, barrels and pistons could be changed readily, making tuning straightforward. Doubling as both a production and competition engine, it was a typical product of the Porsche philosophy.
Indeed it was competition needs that lay behind the first capacity increase to 2,195cc. By 1966 Ferdinand Piëch had graduated from development engineer to technical director, inheriting at the same time responsibility for motorsport. In his ambition to take over his uncle’s role as managing director he set about elevating Porsche motorsport to the top tier in sports-car racing, which would culminate in the famous domination of the 917s and the Le Mans victories of 1970-1. However, he also resolved the early 911’s wayward handing: modifications to the front suspension and, above all, lengthening the wheel base to improve weight distribution removed much of the 911’s tendency to untimely oversteer. Combined with mildly flared wings, the
911 was now able to accept six-inch rims and wider racing tyres, and was suddenly a better proposition for competition tuning. The problem was that Commission Sportive Internationale (CSI) rules at that point did not allow any boring out of the 1,991cc capacity, so Porsche upped this to 2,195cc, putting the 911 in the 2,001-2,500cc class. Homologation rules satisfied, it then built two racing engines – the 2.2 and 2.4 STS – which reliably delivered 230 and 250bhp with a 10.3:1 compression ratio. Racing pistons were used, but the crankshaft and bottom end of the engine remained standard. When the production 2.4 was introduced in 1971, its longer stroke enabled Porsche to expand the capacity of the racing equivalent to 2,500cc. For once, however, this was not a success: the two and a half litre was powerful, developing 275bhp at 7,900rpm (and its maximum torque at 6,200rpm), but was beset by crankshaft vibrations which routinely loosened the flywheel bolts. Paul Frère says that distortion of the magnesium crankcase combined with the weaker long-throw crankshaft meant that a different route would have to be found if the competition flat six was to be enlarged further.
Once again it was more the needs of motorsport than market requirements that drove the next development of the flat six. In 1972, with the imposition of its 3.0-litre limit effectively banishing the all-conquering 917s, the CSI had effectively drawn the curtains on Porsche’s racing shop window. The
company had neither the time nor the resources after the massive expenditure of the 917 programme to design a new sports racer for Group 5. With its new limit the CSI had taken much of the shine off sports car racing. From Porsche’s point of view the logical route seemed to be to develop the 911 to compete in the new European GT championship, but against four- and five-litre Ferraris and De Tomasos more power would be required. In any case, to field a car in the up to 3.0-litre class it would need to have a capacity over 2,500cc. This was the genesis of perhaps the most famous Porsche ever to leave Zuffenhausen: the Carrera RS 2.7. After the troubles with its two-and-a-half-litre competition engine, Porsche was able to create the 2.7 capacity very simply. By changing the cylinder material of the production 2.4S from Biral to Nikasil it was able to bore out to 90mm from the 2.4’s 84mm. Nikasil cylinders had alloy bores and fins with an electronically desposited nickel-silicon carbide bore surface which distributed heat more effectively, and could thus be thinner than Biral, a ferrous compound. The stroke of the 2.4 remained unaltered at 70.4mm and the upshot was an increase from 190 to 210bhp with the same 8.5:1 compression ratio.
A systematic weight-reduction programme at which Porsche was already expert allowed the finished 911 in competition trim to weigh little more than 900kg, and the Carrera RS, as it came to be called, was homologated at 975kg. After fierce internal arguments over whether the 500 road cars needed to achieve homologation would sell, Porsche suddenly discovered it had created a profoundly desirable sports car. The RS was the sensation of the 1972 Paris Salon and 1,590 were eventually built in response to demand, production ceasing only because the lines needed to be reconfigured for the ‘impact bumper’ G-series 911s for model year
1974. What gave the Carrera RS so much charisma was the combination of performance of 210bhp in a car weighing a mere 1,075kg (in road trim) and its strikingly purposeful appearance: it was the first car that German regulations permitted to have wider tyres at the rear than the front and Porsche took full aesthetic advantage, faring the rear arches and adding a rear spoiler – the ducktail – as well as a pronounced front lip. These were no decorations either, with its weight always biased to the rear, the 911’s high speed and cornering stability both benefitted from what were properly developed aerodynamic features. In all respects, the Carrera RS was a highly fitting conclusion to the 911’s first phase.
The G-series represented the first significant styling change in the ten-year history of the 911.
The larger bumpers were forced upon all European manufacturers selling in the US market. Porsche took advantage to update the 911’s cabin at the same time, with revised dash controls and new seating as well as
“The Carrera 2.7 MFI was long overlooked, when in reality it was almost an RS in disguise”
generally improving levels of equipment. Externally new and wider colour schemes were offered, and the skilful way in which Wolfgang Möbius had melded a new front and rear to the 911 was in stark contrast to the clumsy efforts of several other manufacturers. For the G-series 911s the factory once again standardised the power unit, and all models had the 2.7 capacity previously seen in the RS. As previously there were three levels of tune, but the nomenclature had changed. The base T became simply ‘911,’ the middle ranking E became the 911S and the range was capped by the Carrera.
One of the production (rather than racing) reasons for the upping of cubic capacity was the need to carry out a certain ‘detuning’ to meet US emissions regulations. This was a gradual process: the move from 2.2 to 2.4 litres in 1971 had enabled the flat six to function with lower compression ratios and so run on ordinary benzin, thereby producing fewer hydrocarbons from its tail pipe. This went a stage further with the fitting of K-jetronic fuel injection, a system Porsche and electronics giant Bosch had been working on since 1967. By the standards of the day this was a well-designed, reliable mechanism which obviated the need for belt or cogged drives. It was also reasonably immune to interference, an important consideration as more than half of 911 output went to America, where since the late 1960s 911s had to give up their triple
carburettors for a mechanical fuel injection. As federal regulations tightened this too was proscribed. By monitoring air and fuel intake far more closely, K-jetronic supplied a leaner mixture with positive effects on emissions and miles per gallon.
The fact that Porsche still managed to make a sports car which despite federal constraints lost almost none of its power or torque was deeply impressive. The same rules hobbled American muscle cars, and even Mercedes Benz’s 3,500cc V8 SL saw its ‘detoxed’ US version fall from 220 to 150bhp. Nevertheless, the first electronic fuel injection was a compromise on high-revving engines like the flat six, and though the 911 and 911S produced 150 and 175bhp respectively, they lacked the zest of their previous MFI set up. Paul Frère’s ex-r&d 2.4S began life as an MFI 190bhp car, but was converted experimentally by Porsche to run a 2.7 K-jetronic unit. Frère observed that this reduced power to 175bhp and added that though in this guise the 911 had abundant torque, it would not rev anything like as freely as the mechanical injection car.
Almost unnoticed in 1974 was that the top-ofthe-range Carrera retained the Bosch mechanical injection which had been fitted to the Carrera 2.7
RS. Indeed, the G- and H-series Carreras had exactly the same 911/83 engine and suspension as that 911. They weigh roughly the same too, as though the impact bumper shell was only 5kg more than the F-series, lighter trailing arms and other evolutions saved weight elsewhere. That’s why the Carrera
2.7 lost very little performance compared with the competition-oriented RS, one or two miles per hour off the top speed and just a few tenths of a second in the 0-60 dash.
At launch, Porsche did little to distinguish the Carrera visually from its lesser bretheren, though there was a significant price difference. German regulations initially did not allow the cars to run with a ducktail, but when Wolfgang Möbius’s Turbo whaletail appeared, this, together with a pronounced front lip, became standard fare for the Carrera; the 1975 edition certainly looked the part with its optional Carrera script across the doors. It also had Fuchs wheels where the 911 and the S were shod with ‘cookie cutter’ ATS alloys, and underneath it had 20mm anti-roll bars all round – the RS had 18mm up front – and Bilstein rather than Boge dampers (in the UK). The Carrera’s cockpit was distinguished by a handsome 15-inch, three-spoke leather-trimmed wheel. Naturally the Carrera could not be sold with a 911/83 engine to the Americans. They had to make do with a federalised 175bhp K-jetronic version, which Porsche nevertheless priced a daring $1,700 above the 911S. Europe too was concerned about emissions, and Porsche realised the days of free-fueling MFI systems were over. For 1976 it rationalised the 911 range. Making its final appearance, the 2.7-litre engine was confined to the base 165bhp 911, the Carrera took the 3.0 developed for the RS – with K-jetronic this managed 200bhp – and the 260bhp Turbo became the new flagship.
Perhaps because it was simply regarded as an early impact-bumper car, so less desirable than later, larger-engined and galvanised 911s, the 1974-5 Carrera 2.7 was long overlooked, when in reality it was almost an RS in disguise. Indeed it was after 2012, by which time Carrera 2.7 RSS were changing hands for over £250,000, that interest in the ‘other’ 2.7 began to develop. With it came the realisation that the freerevving Carrera 2.7 was the most accelerative of the impact-bumper cars, as quick even as the (100kg heavier) 231bhp Carrera 3.2, but rather more lithe through the corners. It was also a very rare car, with just 1,643 built, which has put on it the Porsche price spiral to the point where an exceptional example such as the one in our pictures is worth four-times a 3.2 in comparable condition.
A brilliant drive and a collector’s gem, clearly today the 2.7 Carrera is a model almost as revered as the RS itself – though only connoisseurs such as you and I are thus far aware of it.
The car in our pictures is currently for sale at The Supercar Rooms. To arrange an inspection call Mark on +44 (0) 1299 666116 or visit thesupercarrooms.co.uk.
ABOVE This lightly restored example has covered 55,000 miles with just one owner
BELOW RS chassis provides a focussed ride. Evolutions in engineering means 2.7 Carrera weighs the same as 2.7 RS despite the addition of impact bumpers
LEFT 2.7 Carreras from 1974 had the RS’S ducktail, while 1975-76 cars got the whale tail, as here