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…

Total 911 - - Contents - Writ­ten by Kieron Fen­nelly Pho­tog­ra­phy by Ali Cu­sick

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.

Thanks

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

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