The Big BMW Coupes

here are many other influences behind the BMW 6-Series, but first we should perhaps piont out that coupes built on production saloon basics — usually at least the floorpan and as many mechanical components as possible from elsewhere in a manufacturer's range — are an especially strong feature of the German motoring scene.

The 501 brought BMW back into car production from a site previously more attuned to BMW aero engine and motorcycle manufacture, its smooth lines hiding a separate chassis and rugged running gear that would later form the basis for BMW coupes and sport cars.

Back at BMW we recall that the fifties saw some dramatic two doors, but with a more overt Chevrolet Corvette sporting two seater style, in the Goertz-penned manner. The 503 and 507 used the separate shassis and all-aluminium encased 90° V8 engine of the contemporary saloons, plus much of the running gear such as the unique steering, gearbox and basic suspension. In the latter case the rear end of the 507 was further modified with Panhard rod and location links to suit a machine that could be geared for a maximum speed of any where between 118 and 137 mph.

Althrough 503 and 507 were very rare beasts, the principle of the larger sporting V8 BMW was carried on into the sixties by the 3200 CS coupe. Built on the same 3835 mm / 111.6 inch wheelbase as 503 (507 was considerably sortened), the 3200 CS was significant. Not for a then considerable 160 bhp at 5600 rpm from eight cylinders, twin Zenith 36 mm carburettors, set up on the highest compression ratio ever offered for the V8 (9:1), but for its styling.

Founded in 1907 and run today by the son of the founder, Bertone in the late fifties and early sixties was home for a new major influence in Italian automotive haute couture: Giorgetto Giugiaro. In 1959, at the age of 21, Guigiaro became the chief stylist at Bertone, a post about as influential on automotive design trends as becoming chief engineer was at VW during the Golf's gestation...

From 1959-65m Guigiaro's Bertone reign under the shrewd guidance of Nuccio Bertone produced over 20 serious prototype of production cars. Best known were the 1963 Alfa Romeo Giulia Sprint coupe and Fiat's 850 coupe, both of which were produced in considerable numbers and exerted a strong influence over later “updates” of their basic lines, or coupes from rival manufacturers.

In the earliest days of his stay, Guigiaro and the Turin team drew, and had manufactured in prototype trim, the 3200. Originally they had both coupe and cabriolet (convertible) prototypes, but only the coupe was made — and then in the usual restricted volume.

The significance to the eighties was in the creation of a large coupe with exceptionally uncluttered lines, an extraordinary amount of cabin glass, and the emphasis on the BMW family look that is basic in the styling / marketing philosophy in Munich, Graf Goertz had dared to drop the BMW Nieren, or kidney-style grille that has existed in one form or another since the thirties, for the 507.

Only three BMW CS coupes were constructed in the Frankfurt Show debut year of 1961, and only another 535 were made before production of the last V8 BMW ceased in 1965. However, this 3300 lb / 124 mph coupe, with its early (for BMW) use of front disk brakes, was far more significant than its production run.

The new BMW coupes — the 2000 CS and 2000 C — appeared in June 1965 to replace the 3200 CS and marked the beginning of a new method of coupe construction for the company.

Althrough the cabin area with acres of glass and the inavitable side rear window curve faithfully echoed the Bertone Giugiuaro style, BMW's own in-house specialist Wilhelm Hofmeister ensured the car had a completely individual model look that was always controversial. At the front it had “chinese” eyes in form of wrap-around headlamps for most markets (many Britisb examples simply had quad lamps). At the back the lamps were superbly blended into the metalwork in a fashion that was to last BMW a full ten years, as was the pillarless (again a Bertone echo) side window treatment.

The 2000 C/CS marked the company's first use of a full production 2-litres (89 x 88 mm = 1990cc), providing 100 bhp with a single 40 mm Solex carburettor and 120 bhp at 5500 rpm with the 9.3:1 cr, twin 40 mm sidedraught carburettor model. These power figures and dimensions would be most familiar to the public in the 2002/2002 TI series.

We said the C/CS coupes were built on the 1800 floorpan and this was reflected in the use of MacPherson strut front suspension and a trailing arm rear end, with a mixed disc and drum breaking system.

The 2000 coupes were phased out in 1969, when it could be seen that the improved perfomance twin carburettor CS had attracted most business with 9999 prudiced as against just 2837 for 2000 CS.

So the 2800 CS, carrying perhaps the sweetest six cylinder engine that BMW produced (a unit that lives in the eighties with fuel injection) began a new BMW coupe legend that was to be really hard for any successor to emulate.

To insert the six cylinder engine in what amounted to a 2000 C/CS from the front windscreen pillar rearward, involved a substantial and beneficial redesign. Overall length went from 4530 mm / 178.3 inches to 4630 mm / 182.3 inches, most of that extra four inches devoted to prising in the still 30° slant six cylinder engine block.

Wheelbase and track were increased compared to the 2-litre coupes too: 2800 CS rode on a 2625 mm / 104.4 inches, a three inch stretch of the original. It had a font/rear track measurement of 1446 mm / 56.9 inches and 1402 mm / 55.1 inches, that near five inch front expansion reflecting the installation of the six cylinder car's front struts and disc brakes, along with 6J x 14 steel wheels in initial Germany production. At the rear the 2800 CS continued with the 250 mm rear drum brakes (9.8 inches) that traced back to 1500, those front 272 mm / 10.7 inch discs of the usual non-ventilated type of the period, and also familiar in other BMW applications.

The six cylinder 2800 CS naturally displayed a weight gain at 1355 kg / 2981 lb, but it was more than offset by the power of the 86 x 80 mm twin downdraught Zenith carburated 2788cc. At 6000 rpm there was another 50 hp (170 total) available from the engine, and that was accompanied by a substantial 1721 lb.ft of torque at 3799 rpm. Enough to carry that big two door coupe toward 140 mph — the factory recorded 128 mph; “Motor” magazine confirmed exactly that figure. The factory only reckoned on 10 seconds for 0-62 mph, but that was over-modest; “Motor” made in 8.5 seconds for 0-60 mph and many others concurred.

The carburated 2.8 sold nearly the same total as both 2000 C/CS had managed, around 9500 in its three season life, before it followed the saloons up the enlarged engine three litre path in 1971. Just as important as the 89 x 80 mm dimensions for 2985cc and an extra 10 hp (180 bhp at 6000 rpm), was the adoption of four wheel 272 mm / 10.7 in. ventilated disc brakes.

Given the capability of those disc brakes and the sheer speed of 3.0 CS it was nice to be able to show before things got completely out of hand...

The 3.0 CSi with its slightly uprated 9.1:1 cr, instead of the usual 2.8/3.0 ratio of 9:1, plus the fuel injection equipment, was rated with 200 bhp at 5500 rpm — saving 500 rpm over the carburated coupe's power peak. Also a meaty 200 lb.ft. of torque at 4300 spm was available, versus the 3.0 CS on 188 lb.ft. at 3700 rpm. The 3.0 CS/CSi was a quick car in saloon of coupe style: BMW reported 136 mph and 0-62 mph in 8 seconds. British road testerd found the car ran out of steam at just over 130 mpg, but there were a few who recorded high 7-second acceleration times 0-60 mph.

However, it was not the commercially-enduring 3.0 CS and CSi machines of 1971-75 that attracted most public attention and ensured that the eraly seventies BMW coupes became such a source of inspired collector bidding in the eighties. Yet they did provide the bulk of the profitable 44,254 coupes BMW sold between 1968-75, as opposed to 252,559 six cylinder saloons made and sold in the same period.

Priority One was made the CSL, L for the German equivalent of Lightweight, and meaning inpractical terms the wide use of alloy panels, Kevlar and other High Tech composite materials.

The first CSLs were seen in the Germany of 1971, but they were not recognised in time to make any difference to BMW racing fortunes during 1972, until BMW had also acquired the Ford Cologne men who were the driving forces behind the Capri's success in lightweight Fird-Weslake fuel injection V6 trim. The key personnel were former Cologne Competitions manager and ex-Porsche long distance team works driver Jochen Neerpasch, who oversaw the development of BMW Motorsport (it was a separate company: BMW Motorsport GmbH) Neepasch was supported by, and left all the engineering expertise, outside Paul Rosche's traditional engine brief, to Martin Braungart, another Ford refugee bored by the Capri's domination as a racing saloon versus a series of modified road cars.

Together with the presence of a man who would go on to scale the managerial heights of Ford of Europe and the parent company in the USA, Bob Lutz, this led to BMW becoming far more aggressive about teir sporting ambitions, and led to another significant strand in the BMW coupe reputation.

The CSL started as merely a lighter CS with a shared 2985cc carburettor 180 bhp power plant, but lightweight panels (including the easily-scarred doors), special seats, sports three spoke steering wheel and 7J x 14 alloy wheels with 195/70 VR radials. Quoted weight for a 3.0 CS has risen to 1400 kg / 3080 lb by this stage, the CSL credited with 200 kg / 440 lb less, which was worth a whole second off the 0-62 mph acceleration time, plus a mysteriousky gained 2 mph on maximum speed (134 mph).

The second stage in CSL development was the 1972 / early 1973 model with a slightly oversize (3003cc) version of the fuel injected engine that differed only from 2985cc unit discussed earlier in an 0.25 mm extra diameter for the bore to give 89.25 x 80 mm. Power, 200 bhp, the 9.5:1 cr, and maximum torque of fractionally over 200 lb.ft. were all unaffected. Weight was up by 70 kg to 1270 kg / 2794 lb, but the sole purpose of this model was to ensure that BMW could race with an engine capacity over 3-litres, whereas the rial Capris were still stuck below this capacity.

BMW Motorsport started the 1973 racing season with a 3191cc version of the straight six engine (92 x 80 mm) tha gave up to 340 bhp at 7800 rpm. This was a little bit more that the Capri V6 could provide after years of development and the fitment of unique alloy Weslake cylinder heads, but still the BMWs had a considerable weight disadvantage — the Ford being homologated for racing at under 1000 kg! Soon BMW Motosport had a 3331cc engine able to race as a result of that oversize 3003cc roadgoing CSL. This Kugelfischer fuel injected unit usually raced with an 11.2:1 cr and up to 366 bhp at a maximum 8200 rpm for its 94 x 80 mm dimensions.

Still Paul Rosche and the Motorsport team wanted more cubic inches, but that was only part of the story for the CSL in its final form. Working with the aid of a short session in the Stuttgart High School wind tunnel, and a racing CSL as a guinea pig, Martin Braungart and his cohorts produced a fantastic aerodynamic wing set for the racing BMW. In order that it should be recognized for racing as from July 1st 1973m a series of road cars had to be produced and these ultimate CSLs also carried the longer stroke six cylinder engine.

With an 89.25 mm bore and 84 mm stroke the road power unit was uprated with 206 bhp at 5600 rpm from 3153cc. More importantly in road and race terms, torque was also increased: for the road car there was 2111 lb.ft. at 4200 rpm, whilst the racers were bored to a full 94 x 84 mm for 3496cc and would provide 370 bhp plus lashings of torque with a slightly lower peak (8000 rpm) than the 3.3 litre predecessor.

Certanly this 370 bhp helped win races against Fords that were unlikely to have more than 320 bhp, but it was the “Batmobile” wing system that demoralised all shred of opposition. Braungart confided that the front and rear spoilers, plus the wing, were the vital components, providing such downforce on their own account that BMW could frequently run softer sompound tyres that the opposition. The advantage if such a wing system over a Capri with a front spoiler only, can be imagined, especially around the Nurburgring's hilly curves.

For the July 1973's edition of the Nurburgring 6 hours both Ford and BMW pulled out all the GP names they could find, Alpina — BMW running a then BRM GP driver, Niki Lauda. The eighties McLaren Formula One ace then pulled out pole position for the Alpina CSL, setting a time of 8 minutes 17.3 seconds against 8 minutes 23.0 seconds for the fastest Ford, which was the machine for Jochen Mass, rather them two of the world's quickest men at the time, who were also co-opted into the Ford fold: Jackie Stewart and Emerson Fittipaldi.

So the wings worked well, right from their debut, and Ford were destined not to win another European Championship round that season...

The road version of the last CSL had the 3.2 litre engine mentioned, plus plastics for most of the additional aero kit and the usual aluminium ligtweight panels. Again weight was quoted at 1270 kg. The road 3.2 litre CSL came with the usual spats over the wheelarches, rather than the huge wheelarch extensions favoured by racers, and thus popular for road cars of subsequent decades. The standard wheel was a 7J x 14 inch alloy type with 195/70 VR radial tyres. The interior was upgraded as before with sports front seats and a rather more dashing design of steering wheel, but the 10.7 inch vented disc brakes and ZF Gemmer worm and roller steering remained as for lesser production coupes.

Perfomance of the later big-engined CSLs was considerable: 0-60 mph occupied a scant 7 seconds and top speed was usually recorded as 138 mph without the wings, or slightly over 140 mph with the wing kit installed.

Unusually even the factory ran these obsolete machines in 1976, whilst privateers carried on with the 3.5 litre racing motor and the full wing kit to win European Touring Car Championship titles until 1979.

In racing guise the big BMW coupe was extremely popular and very spectacular. It was the best racing saloon in terms og long-lived results that BMW have ever had, and it very nearly put one over Porsche when campaigned in 1976 Group 5 races. Work started on a four valve per cylinder M49-coded six cylinder engine in September 1973 and over 400 bhp was provided immediately even by the 3.2 litre prototype. Despite the fuel crisis cutting race budgets sharply, the 24-valve M49 was debuted in two CSL's for the April Australian European Championship round and gave Hans Joachim Stuck / Jacky Ickx a win with some 330 bhp available at 8500 rpm. The power unit was further developed to provide a reliable 470 bhp at 9000 rpm, when mounted vertically, instead of at the normal production 30° slant, with new water channeling to combat overheating and a far straighter run for the top exhaust manifolds.

The full benefits of vertical engine mounting became apparent in 1976 when BMW supported the efforts of three well financed teams in Group 5 CSLs to take on Porsche, and fielded their own development car. This was the ultimate CSL. Coded M49/4 the engine thundered forth 750 to 800 bhp from 3191cc in race trim, and was equipped with KKK turbocharging. It only raced three times, notably inthe hands of the late Ronnie Peterson, but was perhaps the most sensational saloon a manufacturer has ever fielded with the ability to fry the driver's feet and produce strong acceleration wheelspin in third gear, with flames to delight the onlookers throughout!

Whilst the turbo did not lead to any great BMW pruction quest in itself — the 3210cc turbo 745 i is a very different (252 bhp) luxury saloon — the four valve six cylinder unit had bacome increasingly important since the CSL and cousins ceased their elegant road and track perfomances.

For, as we shall see, the four valve six became the basis for the M88 production equivalent for the M1 supercar. That led to a 6-Series sporting such a 24 valve power plant in 1983, but with a powerplant updated in many detail respects over the original mid-engined M1 application.

Unfortunately there does not seem to be a racing opening for the unit in M635 in 1984, but the spirit that made the 6-Series such a prestigiously important introduction to BMW can clearly be understood from the astonishing and long lived versatility of the 1968-75 coupes.

Source: BMW 6-Series

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