ROADTEST

BMW 633 CSi

Bavaria’s flagship gets a 5-speed gearbox.

(Road & Track Special, 1982. USA.)

Things are quiet at BMW. It has been four years since a fully new model has been introduced in the regular series-production line. The 633 CSi, BMW’s luxury-sports coupe and top of the current American model lineup, was introduced in early 1976 in Europe; a 3.0-liter version of it (the 630 CSi) came to America in 1977 and the 3.2-liter edition now sold here has been on the North American market since 1978.

   Each year, however, the big BMW coupe gets detail improvements. In the 1980 Guide a significant improvement in fuel economy and driveability was noted, thanks to last year’s change from thermal reactors to a 3-way catalytic converter with oxygen-sensor feedback for emission control. For 1981 the mechanical changes are limited to adoption of the 5-speed gearbox that went into the 528i in 1980; a ZF 3-speed automatic remains optional, and with it cruise control can be ordered. There are also some minor interior and equipment changes such as a digital quartz clock replacing the “old-fashioned” dial type, revision of the central locking system to provide locking and unlocking from the right door or trunk lock as well as the driver’s door, and adding a little light to the ignition key that points the way to the ignition switch when a button on the key’s side is pressed.

   As time goes on and the general downsizing process continues, the BMW coupe – already a step up in size over its predecessor, the 3.0 CSi – looks bigger and bigger. Nor is its weight modest by current standards. But its proportions and styling are outstanding, and the recent mechanical changes have helped keep its fuel efficiency high enough that the clientele for a $40,000 car seems to find it quite acceptable. Perhaps more to the point, the 633 CSi is the fuel-economy leader in its class, despite its ample dimensions. Credit goes to its relatively modest engine size and its standard 5-speed gearbox, a device not available on most of the competition.

   All of its direct competitors – Porsche 928, Mercedes-Benz 380SL/SLC, Jaguar XJ-S – have bigger engines and more cylinders. In the past few years, indeed, BMW has experimented with more complex engines, building a 3.9-liter V-8 and a 4.5-liter V-12 as production proposals before deciding against them. Now the Bavarian maker has publicly decreed that six cylinders will be its upper limit, a decision influenced by both the long-term energy picture and BMW’s expertise in the inline 6-cylinder configuration.

   As an example of what can be done with the engine type, the 633 CSi’s “big six” lends credence to BMW’s position. Part of the company’s pitch for six cylinders is that this count provides almost as much refinement of operation as eight or 12, and this engine’s smoothness supports the pitch. You know by its sound that it’s a six, but the sonorities are interesting and virile and the delivery of power is butter-smooth right up to the point where the ignition cutout punctuates the exercise (at 6200 rpm, down from the previous 6400). Performance remains unchanged and strong; the 633 CSi handily breaks the 8.5-second mark in reaching 60 mph from a standstill.

   In general, the emission control by 3-way catalyst and oxygen-sensor feedback allows the BMW six to run well and respond spontaneously to the accelerator pedal. But this test car did have one hitch, in that its engine ran rather unpredictably after a cold start. Idle speed fluctuated widely, and as the engine warmed up the speed fluctuation moderated into mere roughness and finally gave way to a normal, smooth idle. Even at that, though, the speed (1100 rpm) seemed too high, and a heat shield under the catalytic converter rattled as the engine idled.

   Aside from this problems, the 635 CSi was as pleasant as ever to drive – indeed, thanks to the new 5^th gear, more pleasant than ever. In the first four gears, except for an insignificant change in the 1^st gear ratio, overall gearing is the same as before. Likewise for shifting, which is wonderfully smooth and precise – including getting into 5^th. The overdrive 5^th reduces engine speed by 19 percent, increasing highway and suburban mileage (our test mileage was up from 19.0 to 20.0 mpg this year). But it has little effect on the CSi’s already moderate noise level. In fact, at certain speeds it can even increase engine noise coming into the car. At 30 and 70 mph, for example, we got readings 1 decibel higher in 5^th than in 4^th, a difference attributable to the engine’s exhaust note, which at some speeds intensifies noticeably with a little extra throttle opening. (To maintain the same road speed in 5^th gear, more throttle opening is required – that’s why an overdrive ratio gives better fuel economy.)

   In urban driving the coupe’s large size sometimes makes it a little difficult to find a suitable parking space, though its huge glass areas do make it relatively easy to maneuver into a tight space. But it is on the open road where this GT car truly shines. If we in America were allowed to drive fast, the BMW could strut its stuff as it does in its homeland; here we must make do with its relaxed mechanical sounds and good directional stability at American-style freeway speeds and the competence it demonstrates on winding rural highways.

   This competence is provided by BMW’s traditional attention to suspension, brakes, steering and body integrity. Like other “normal” BMWs (that is, excluding the M1), the 6-Series coupe has MacPherson struts at the front and semi-trailing-arm independent suspension at the rear. For the North American market only, BMW fits BBS-Mahle alloy wheels with 6½-in. rims; they are shod with Michelin XVS tires in place of the XDX formerly used. The change in tires – the new ones are less expensive and not capable of sustaining extreme cruising speeds – was made to save weight, according to BMW, and we did not find any marked difference in the way they handled.

   In normal-to-brisk driving on winding roads, then, the 633 CSi remains basically the same: responsive, stable and capable of high cornering speeds. BMW’s variable-assist power steering, with decreasing assist at high engine speeds, contributes to the good impression by retaining plenty of road feel at all speeds. But as one approaches the cornering limits, BMW’s chassis philosophy requires increasing expertise at the wheel to cope with the final oversteer. In tight, low-speed corners, the characteristic manifests itself as the lifting of the inside rear wheel, a bothersome trait that can be dispensed with only if one does not drive so energetically or does order the optional limited-slip differential.

   Most people – in particular, most Americans – will never encounter any of this. Nor will they ever experience the CSi’s braking limits, which are also high. Its stopping distances in “panic” situations aren’t the world’s shortest, nor are its brakes utterly free of fade, but they do a good all-around job – as they should, with their large-area ventilated discs all around. Stopping distances could probably be improved by the use of wider tires, but BMW has not followed the trend to the sportier 60- or 55-series tires used by some makers of sporting machinery.

   The CSi’s cockpit typifies the contemporary BMW approach to the driver’s working environment and passengers’ accommodation. BMW puts special emphasis on driver ergonomics, curving the instrument panel in plan view so that everything is within easy reach. Instruments, both the large main ones and the smaller dials, are easily read, and all of the controls are logically arranged and pleasantly precise in operation.

   Most of the coupe’s interior materials are plastic of one kind or another. In its contours as well as its functional aspects, the padded dash is a remarkable example of what modern manufacturing processes can accomplish. The door and side panels, though beautifully thought-out and flawlessly assembled, tend more to the austere than the lavish. And the seats don’t convey any of the boudoir effect one finds in domestic luxury coupes of similar size, but their leather-upholstered contours were designed with comfort and good support in mind.

   Standard equipment in the 635 CSi is extensive: air conditioning, electric window lifts, a 2-way electric sunroof (that lifts at the rear or slides open), electric outside mirror, central locking, power-assisted steering, metallic paint and a comprehensive radio-cassette stereo system are all on the long list of items included in the basic price, with automatic transmission (a 3-speed ZF device) and the limited-slip differential the only optional items. One thing, however, causes BMW owners some grief. Because the radio is of high quality and easily adaptable to other cars, the theft rate for the stereo system is high.

   But so is the general satisfaction of 633 CSi owners with their luxury GT coupes. Our only reservations concern its large size, small fuel tank and (despite the improvements) a rate of fuel consumption that can only be justified by its high performance and considerable luxury. Of course its price ($35,910) is high too, but the dollar’s dramatic comeback over the past year should at least give it price stability for a while.

BMW 633 CSi (USA 1982)

General

Engine

Drivetrain

Road Test Results

Acceleration
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