A NEW COUPE FROM BMW

Technical analysis & driving impressions of the 630 CS and 633 CSi.  

(Road & Track, June 1976. Ron Wakefield, European editor. USA.)

The old BMW coupe, known most recently as the 3.0 CS, had been with us in one form or another for 10 years, and though it was still a nice car its time had come. As retiring chief engineer Bernard Osswald of BMW put it, “Let’s face it, the old coupe was no longer at the forefront technically.” It first appeared in 1965 as the 4-cylinder 2000 CS (for Coupe Sport), related to the 2000 sedan. A very glossy passenger cabin, much wood trim inside and clean body lines from the cowl rearward were its strong points; less impressive were its awkward front-end design and an engine that seemed too small for the car’s weight.

   When BMW’s first postwar 6-cylinder came out in 1968 the coupe was adopted into the new series. It got a harmonious new front end, new front suspension and a 2.8-liter 6-cyl engine, although the old rear suspension and drum rear brakes remained, and thus became a much more attractive car. It has continued in essentially this form ever since. The engine grew to 3 liters, the rear wheels acquired disc brakes, and there were eventually variations ranging up to the wild, winged 206-bhp CSL and its racing counterpart – which, incidentally, is still winning races. But any good car is eventually overtaken by better technology, and the latest BMW sedans were better cars than the top-price coupe.

   The Bavarian firm, which had a record year in 1975 and shows no signs of slowing down, has now corrected the situation with a handsome new coupe. Available presently in Europe in two versions, 630 CS and 633 CSi, it is not (as had been rumoured) based literally on the 530i sedan, although it shares basic technical characteristics and the floor stampings immediately under the passenger compartment. It’s more likely that the new coupe will have considerable component interchangeability with a new series of large BMW sedans, probably to come along sometime in 1977 to replace the current 3.0 Si and its siblings. Like its predecessor, the new CS will be assembled (and its body manufactured) in small quantity at the Karmann factory in Osnabrück rather than one of the BMW factories in the Munich area. As recently introduced BMW sedans like the 530i also outstripped the old coupe in assembly quality, it’s to be hoped that updated production techniques used for the new one will bring it into line.

   Built on the same 103.3-in. wheelbase as the old model, the new CS is predictably slighter larger: 4.5 in. longer, comparing European-specification cars new and old, and 3.0 in. wider. Thus in the normal sense the new car is a logical successor to the 3.0 CS, though in these days of ever-climbing fuel prices one might have hoped for a lighter, more compact car. In appearance it could be nothing but the new BMW coupe. The characteristically glassy look continues, even though pillarless coupes are now passé and the new one has a central roof pillar / rollbar. In fact, glass area is up 7 percent. Bronze-colored tinted glass is standard, and BMW people admit freely that this was chosen because it looks better: it is only 60 percent as effective as the usual green. It does look good; and the customer who must have green can still order it.

   The shape is also related to the latest sedans, with its low and sloping hood, the virtually square BMW “kidney” grille center and raised hood section leading back from it, the wedge side profile and squared-off tail end. Sides are lean and clean and the windows drop below the main beltline. Only at the rear is the form somewhat disaccordant: the rear bumper looks unrelated to the front one. Here you see the chrome European bumpers; for the North American version there will be aluminum ones on hydraulic energy absorbers, protruding about 2 in. farther at each end and thus not nearly as prominent as those of the 530i or the 1974 3.0 CS USA. (No 1975 coupes were sold in North America.)

   Inside, the concept of a luxurious 4-seater is continued but there is significantly more leg, head and shoulder room in the rear shell seats. As before there’s a fold-down center rear armrest; new are adjustable head restraints, behind which molded shells blend into the package tray and lift up to reveal two small compartments for odds and ends. The front seats, with their widely adjustable head restraints, are as before generously dimensioned and comfortable; the driver’s seat has inherited a manual height lever from the 530i. This 2-way lever allows not only the height but the angle of the whole seat to be set, and in combination with separately variable backrest angle and a telescopically adjustable steering column leaves little “room” for complaint about driving position.

   The old coupe was rich in wood inside, with paneling across the dash and along the sides. In the new one there is no wood at all, but rather the latest in padded, ergonomic, plastic contours. The dash looks very much like that of the 3-series BMW (yet to appear in America as the 320i), its instrument-control board wrapped slightly so that the driver can reach everything easily, and the contours of this section also wrap around into the doors to give visual continuity. Above this are several air outlets for the heating-ventilation system, which is greatly improved. Directly in front of the driver are the three instrument dials, orange illuminated at night, and the main warning lights. To the left is a new set of “monitor” warning lights, reminiscent of those in the Toyota Corona hardtop though not as complete. Here the driver can check the level of four important liquids – engine oil, coolant, brake fluid and windshield-washer fluid – plus the condition of the front brake pads and operation of brake- and taillights by pushing a single bar labeled “test”. If anything is amiss (fluid low, pads worn too far, bulb burned out) its light does not come on. BMW’s philosophy here is that if one of the warning lights itself is burned out the driver will begiven the pessimistic message and therefore be warned of a possible problem. If the bulbs were to light only when there’s trouble and one were burned out, he would be given a false sense of confidence.

   BMW has given the optional air-conditioning system more attention than it got in the old coupe, not a bad idea as the old one couldn’t keep front passengers cool at more than 90 degrees outside without sounding like a hurricane and never mind the folks in the rear. Though not a fully integrated system in the American sense, it is now controlled by the same temperature and blower controls as the heater and its cooling capacity is up from 4500 kilocalories per hour to 6200, a meaningful 37-percent increase. Air distribution is also much better: cooled air comes from outlets at both ends of the dash, the main center grille and a small center one directed at the driver instead of a single center one. BMW and Behr cooling engineers developed the new system partly in Texas and Arizona, so there is hope for it. Another item very popular in America these days, the sunroof, has been changed for the lift-or-slide type. And there is provision for four built-in stereo speakers.

   The trunk, beautifully finished but not large in the old coupe, is just as well finished in the new and about 23 percent larger. On the underside of the trunklid one still finds the clever drop-down toolbox, an idea of former U.S. importer Max Hoffman, with its fascinating assortment of ordinary and special tools plus bulbs, fuses and sparkplugs. The fuel tank remains under the trunk floor, bucking Mercedes’ trend to over-the-axle placement, and is actually slightly smaller than before.

   Of course there are the usual safety improvements like longer “crush zones” front and rear and a stronger passenger cell. The rollbar, finished in matte black and thus de-emphasized in the car’s styling, provides roof strength for U.S. safety rules as well as a better place to hang the front seatbelts, and as a side benefit stiffens the body. Although the pillarless CS was remarkably rigid for such a structure, according to BMW engineers the new one is 31 percent stiffer in bending and 69 percent better in twisting.

Engines & Transmissions

For the European market there are two engine choices. The 630 CS has the familiar 2986-cc inline six single overhead cam, now fed by a 4-barrel Solex carburetor like that of the Mercedes 280 instead of the previous Solex 2-barrels. This boosts the power from 180 to 185 bhp DIN, allows a lower fast-idle speed (and thus hopefully avoids the ominous noises carbureted BMW sixes make when started from cold) and reduces emissions. The 633 CSi engine is the 3210-cc injection six recently introduced in the 3.3 Li over here (why not, then 3.2 Li and 632 CSi?) and produces 200 bhp. When the coupe appears in America it will most likely have the same detuned 2986-cc injection unit now used in all North American 6-cyl models. The decision is not firm yet, but if so the name will be 630 CSi and the power 176 bhp SAE net.

   The manual 4-speed gearbox is like that used previously, but the automatic is new and completes a transition from the Borg-Warner 65 to a new ZF type. Also a 3-speed unit with torque converter, the ZF is lighter, more compact and smoother-shifting thanks to its Simpson (instead of Ravigneaux) planetary gearset, an arrangement long since normal in American automatics. The final drive ratios are 3.45 : 1 for the 3-liter, 3.25 : 1 for the 3.2 and probably 3.64 : 1 for the heavy-breathing American version.

Chassis

Ever since BMW brought out the 4-cylinder 1500 model that effectively rescued the company from financial ruin in the early 1960s, BMWs have stuck with a basic combination of MacPherson strut front and semi-trailing independent rear suspension. The new CS models hold to this formula with refinements. The front suspension geometry is altered for better straight-line stability and better behavior in the event of uneven braking, but the layout remains the same with simple lower lateral links, drag struts and the MacPherson coil-shock struts. The shocks are now easily exchangeable to simplify replacement; spring travel remains at 7.9 in. and the anti-roll bar is very slightly larger. As before it is mounted to the lateral links with rubber above and below it so that it does not come into play on small bumps or gentle road undulations. Only when the rubber is fully compressed does it begin to act as an anti-roll bar, thus avoiding some of the harshness a bar can introduce on one-wheel bumps.

   At the rear, all the components are new and the coils and shocks are now concentric as in the 3- and 5-series. An anti-roll bar is standard here too, as it has always been on the U.S. version of the coupe. Springing has been softened slightly at the front and stiffened at the rear to get rid of the old BMW pitch, and there’s now more spring travel at the rear: 8.5 vs 7.9 in. The rear track, formerly much narrower than the front, is now considerably wider.

   Brakes have been improved in an evolutionary way too. The front (ventilated) discs are now 11.0 in. in diameter vs 10.7 before, and now all versions have the 10.7-in. vented discs at the rear. BMW has stuck with the same wheel and tire sizes: 195/70 VR-14 on 6-in.-wide rims. The engineers say that at the moment they aren’t charmed by wider tires, such as the 60- or 50-series, for this sort of luxury GT. But “at the moment” seems significant, perhaps hinting that a sports version like the 3.0 CSL is in the offing. Alpina alloy wheels are standard.

   Power steering is now standard and has been changed to the recirculating-ball type used in the 530i. The ratio is thus reduced from 18.1 : 1 to 16.9 : 1 and the wheel turns lock-to-lock are cut from 3.7 to 3.5. More interesting is that the “assist curve” of the power-steering pump has been recalibrated so that power assist falls off with increasing engine speed. Up to about 2000 rpm it delivers 100-precent boost for easy parking and low-speed maneuvers. From there up to the engine’s redline of 6500 rpm the assist is smoothly reduced to 70 percent of maximum, so that at high speeds the steering communicates a firmer feel to the driver. Up to now only Citroën had offered such a feature.

   The new coupe is 110 lb heavier than the old, partly because there’s more sound insulation and partly because it’s bigger and stronger. It can also be expected to be more expensive and most likely will cost around $20,000 in the U.S. with full equipment (air conditioning, leather upholstery, stereo, electric front window lifts, etc).

Driving impressions

Aside from audible air turbulence around the windshield and variable quality of sealing around the door windows, the old CS was an exceptionally quiet car, and with about 40 lb more sound-deadening one would expect the new one to be quieter. As far as wind noise goes it is, with the qualifier that if I lowered a front window after closing the door the rubber sealing no longer worked on the two prototypes I drove. Otherwise the new car seems to be, if anything, a bit noisier. The differential sang a hearty song in both cars, and in the fuel-injected model a lot of engine noise came through too, although it was the virile sort of noise an enthusiastic and fast driver can enjoy. Using the car speedometer, I timed the 633 CSi with manual gearbox as follows, shifting at 6500 rpm:

  The shift linkage was a bit stiffer than in the older car, perhaps because of newness. In any case the BMW six and manual gearbox remain a sporty, satisfying way to get a lot of performance from a moderate-size engine in what is a relatively large car by European standards.

   For contrast I tried the 630 CS with automatic, which probably approximates the performance Americans will get, and found it would attain 60 mph from rest in 9.4 sec with or without manual gear selection. This engine is quieter than the injection unit; it doesn’t sound as “hard”, but still a lot of exhaust noise came into the car just as in the 530i we tested last year. The new automatic is decidedly better than BMW and Borg-Warner’s mediocre past efforts. On moderate acceleration it shifts very quickly out of 1^st gear, like earlier BMW automatics, but it does stay in 2^nd longer and thus gives a less strained effect. With the foot firmly planted on the floor it upshifts both times at 5700 rpm, making manual override unnecessary for maximum performance, and kickdown to 2^nd for passing is available to 75 mph. With the 4-speed 633 CSi I reached an indicated 220 km/h (136 mph), with the automatic 630 CS 200 km/h (124 mph) on the long straights of BMW’s bone-shaped high-speed track.

   Going to the handling course, I wanted to see if the new power steering would make the car tricky to handle in the sort of hard driving on a curving road in which one changes gears often. I’d found the steering feel very good at high road speeds, though there was no crosswind to really test the car’s stability, and by running along at steady speed in one gear and then shifting up or down I could feel the difference in power assist – but it was pretty subtle. Changing gears while turning the steering wheel failed to unearth anything that would come to consciousness if one weren’t looking for it, so I’d say BMW has accomplished this improvement in power steering without introducing any dangerous or bothersome side effects.

   BMW’s characteristic final oversteer is there, but this is something one experiences only with energetic provocation. The handling course also includes a good sample of bumpy curves; their effect on the car is virtually nil even when cornering at the limit, the people platform remaining supreme stable. I found the brakes less impressive; they’re powerful but too easy to lock up on a hard stop. Overall, the ride – which I checked over bumps, dips and cobblestones – is slightly better, mainly because the old tendency to fore-aft pitching is gone. Ride development seems to be on a plateau, although a very high one, with sophisticated independently sprung cars such as this one.

   The old coupe’s electric window lifts, particularly after 1973, were hopelessly slow. Unfortunately they now seem to be worse – I timed the meager 5-in. descent of the rear-quarter panes at what seemed an eternal 5.5 sec. No cars with front lifts were on hand. Otherwise, though, there’s little to complain about in the CS’s interior. It’s roomy up front, usefully more spacious in the rear. Instruments and controls are laid out beautifully, the seat-height adjustment and telescopic steering column make it possible to find just the right combination, and you can impress everybody on the block with that panel of warning lights. Ventilation is superb with all those air vents and works very quietly, but I had no opportunity to try the air conditioning.

   The new BMW coupe carries forward its predecessor’s blend of performance and refinement with worthwhile improvements in comfort, styling and safety. If it seems large in the European context, in America it is a car of moderate size and weight considering how luxurious it is, and of course a chassis of this sophistication is simply not available in a domestic car.