You have ambled through town and village with perfect manners, the car comparatively unobtrusive, the engine typically smooth and entirely flexible in the 23.9 mph per 1,000 rpm fifth, even at 20 mph.

   Now it sits, idling quietly, short aluminium alloy gearlever in first, the only uncouthness being the effort needed from your left leg (42lb) to keep the clutch pedal shoved to the floor. You don’t floor the accelerator, yet: more than 3,000 rpm, and the wheelspin is dramatically lurid, snakey and wasteful of time. You ease it off at just 3,000, then back off slightly to help those meaty TRXs grip, flattening the pedal finally at around 4,500 rpm torque peak as the car rockets up the road, the previously docile engine howling in a deliciously exaggerated accent on the usual BMW-six noise, all the way to the 6,900 rpm rev-limiter-backed red line.

   Bang the lever into second just short of 40 mph with a squawk from the back tyres, revs still high at 4,100 rpm, the less easy next change into third only 3½ sec away, passing 60 only 6.1sec from the start. Third hurls you on to a shade before 100, at 15.6sec, incredible for such a big, weighty (30cwt) car; fourth through 110 before 30sec. Snatch fifth, and 140 passes at 41.8sec as the car roars its way on to the 156mph maximum, the clear road blurring under the broad nose.

   Yet when conditions change again, no matter how quickly after flat-out, there it is again – that same coolly relaxed, refined tractability, without temperament. The power and torque peak speeds suggest a peaky delivery, with little low speed pull, and the noticeable step of valve overlap effects as the power comes in. It is an exhilarating engine, with obviously more go from 4,000 rpm onwards, but it performs pretty well from as low as 2,500, and the progression from the good to the spectacular is comparatively subtle.

   Although BMW plan to make the M635 available (in left-hand drive only) here eventually, it goes on sale only in Germany now at 89,500 DM (roughly £23,000). This test was conducted in Bavaria last November, so we had some truly cold starts at below freezing. The engine started as perfectly then as all modern Bosch-injected cars do, but unlike the rest, it did need a momentary prodding encouragement from the accelerator to keep it running whilst frosty windows were being cleared. This was its only hint of any kind of temperament, and it proved to be no more than a moment of hesitation. Otherwise there are no flat spots, nothing but entirely controllable urge, bags of it.

   Overall, in fifth, it turns out to be perfectly geared, the maximum speed corresponding to 6,550 rpm, 50 rpm above the power peak. As explained in the noise section, when one is using the performance by cruising above 100, on the odd occasion the comparatively high engine note induces one to try to change up from fifth. The gearchange is mostly good, except that when hurried, it can baulk, refusing second, or when that doesn’t happen, showing slight synchromesh weakness. To be fair however, this particular car, at the time only the second M635 built, had been tested by at least three other magazines, so its life had been untypically hard, as the departure of the leather-covered knob from the gearlever further suggested; we mended it successfully with “rapid” Araldite.

Economy

Most likely M635 customers will not be preoccupied with good fuel consumption figures, and if they drive the car as we naturally did during the performance measuring part of the test, they will not be surprised to return figures like 13.9 mpg, our worst. On the other hand, it wasn’t difficult to achieve 22 mpg in more normal if still typically fast driving. The tank holds the standard 635’s 15.4 gallons, which is a little on the low side for this sort of thirst if one is using the performance. We noted some post-over-run blue smoke from the exhaust when following the bmw, and oil consumption turned out to be unusually high for today, at 700 miles per litre (400 miles per pint).

Refinement

As a sporting – very sporting – luxury coupe, the M635 seems to our taste to have the right compromise in engine noise, pleasingly muted at low to medium speed, and only becoming anything like loud as one goes faster – but the sound is that particularly lovely one to the red-blooded driver, of a lusty straight six. It is always smooth. Stroke the M along gently, and you would really not suspect that there is anything rouse-able under the bonnet. Foot it flat, and there arises the usual delightful BMW yowl, but much stronger than before, and accompanied by a remarkable hard mechanical edge to it, suggesting a crowd of little hammers all at work; you hear it too on the over-run. At around 130 mph, the cruise is spoilt by some heterodyning.

   The car disappoints in its suppression of wind noise, which on the test car was particularly bad from around the windscreen pillar door seals.

   In interesting comparison with the opening roof of the automatic 635 CSi also tested in this issue, which was equipped with a conspicuously large, fixed deflector, the unshielded opening of the M635 sunshine roof, whilst understandably wind-noisy, also does not suffer from the usual very low frequency organ-pipe flutter. Road noise is present, but not as much so as the car’s stiffer suspension and tyres might make one expect.

Road behaviour

As usual with the standard 635, the assisted steering is surprisingly heavy by power standards, but not too much so; it fits the character of the special M635 steering wheel, with its thick rim. It is fairly well geared, at 3.2 turns for a minimum turning circle of 34ft 10in. dia (to the left – the test car’s lock stops were very asymmetric, with a 37ft 5in. dia right-hand circle), and has all of that typically eager BMW turn-in, without feeling unstable in most circumstances. It is accurate, and mostly very straight-stable whatever the speed, except for what seemed to be a surprising sensitivity to any change of camber in the road, which deflected the car noticeably, in a suggestion of the way of cars of three decades ago.

   The combination of the reduced semi-trail angle of the rear suspension plus the slightly lower centre of gravity of the coupe – plus in the case of the M version, the reduced wheel movement of stiffer suspension – gives the most powerful 635 even less of a tendency towards unwanted tail-out slides due to wheel camber change than the standard car, which does seem to be better than before. One can still induce such slides by deliberately clumsy driving, and the M is no car for a lead-footed novice, especially in the wet, when it has obviously to be treated with great care. But its excellently progressive throttle linkage makes it easy to drive carefully, so there is little excuse for stupidity.

   Traction with a powerful car is as much a matter of keeping the amount of tyre tread contact reasonably large and constant, which is why cars with low camber change rear suspension are always less prone to wheelspin for the same rate of acceleration, power-to-weight and tyre load than cars with higher camber variation. The BMW cannot be expected to pull all of its 170 bhp per ton laden through even those back tyres without spin, but one cannot help suspecting that it could be better with, sy, a de Dion rear end.

   The stiffer springing is very obvious at lower speeds, with a distinctly joggly ride that contrasts noticeably with the comfort of the standard car. As there is only just enough headroom for our 6ft testers, the firmness of the ride at all speeds makes such people hit their heads too easily. But given the sort of car it is, the ride deterioration is not unacceptable.

   Brakes are fitted with Bosch ABS anti-lock which once again is a damage and embarrassment-saver when the unexpected happens too close. There appears to be a small loss in ultimate braking ability, as usual, so that we could not better 0.95g, which is not as high as one might expect from this tyre equipment. ABS may well help however, especially for any driver who has not got used to the car when an emergency occurs, since the response to pedal effort is rather abrupt, with just 10lb producing a 0.15g slowing, jumping to 0.4g at 20lb, and 0.7 at 30; the curve does however flatten slightly above this, and anyway the anti-lock system is there as the ultimate safeguard beyond. Fade resistance is just good enough, in spite of the pads beginning to catch light at the end of our performance-related fade test.

Behind the wheel

Anyone familiar with the normal 635 will feel at home straight away, since the interior differences are small. Most obvious is the thicker-rimmed steering wheel. Steering column rake adjustment on the test car didn’t work, so for taller drivers the wheel was rather low, and blocked the view of the top of the speedometer and rev counter. The test car was fitted with superb Recaro seats, with plenty of firm side support, the ability to tilt the whole seat as required – although not raise it – plus the unusual feature of thigh support adjustable for length. Pedals are perfectly arranged for heel and toe, which the delightful response and voice of the engine makes a particular pleasure. Driving position is typical German – high and commanding.

   Rearward movement of the driver’s seat is adequate for up to 6ft types, but as mentioned already headroom is a little tight, at any rate when the extra equipment Recaro seats are fitted.

   By the standards of high-performance coupes, the view out isn’t bad, although the thickness of the windscreen pillars is something to beware of, and the car lacks the wonderful all-round vision of the very slender-pillared old CSi of the last generation.

   The heater is a sophisticated water-valve-controlled type, which means that the response to any movement of the temperature control is not rapid, as it is with an air-blender, but thanks to thermostatic control, one can achieve the desired temperature. It is good to find that this German car does not have warm air bled into its face level ventilation when the heater temperature is adjusted towards warm.

Living with the M635 CSi

The interior is very well planned, for two at any rate; space in the back is strictly for the occasional occupant who doesn’t mind sitting hunched up for a short while. There is the usual very ingenious BMW service indicator system, whose lamps tell the driver when service is due, based not just on time or mileage, but on how he or she has used the car.

   Electronic entertainment equipment fitted to the test car included a magnificent (and expensive) Blaupunkt Bavaria radio-cassette player, and BMW’s equally extravagantly priced trip computer (£516 in this country, or about the same as a desk-top personal computer with some of its peripheral equipment).

   Oddment accommodation is good. Electric windows are fitted, and they wind up or down in 3½ sec, which is reasonably rapid.

   Open the bonnet, and there is a treat. The engine is the rare sort that owners will delight in showing off – it looks very handsome, almost as good as the way it propels the car. Detail design is tidy and neat, so that finding things is not difficult. Particular points to note are the multi-pipe exhaust, and the long (11in.) inlet tracts. The dipstick is easy to find. Anyone unfamiliar with BMWs must note the way in which the bonnet is shut, not by slamming, but by leaving it resting in the shut position, then locking it from the cockpit my moving the lock lever under the dash.

Comparisons

The range of cars available to the man who is interested in this sort is limited. If one restricts oneself to the over 150mph rarities, then the variety is wide in one sense – price and type – and narrow in another – the small number of cars that have such a top speed capability. In our overall list, we have broadly speaking concentrated on machines which are more of the BMW ilk, which means the bigger, more comfortable, luxurious Grand Tourers which have the performance, the size and the space. For this reason, Porsche are represented only by the 928S, and we have omitted the 911 Turbo, practical and immensely fast and efficient as it is (162mph;5.1sec to 60;16.4mpg overall). Lotus are borderline cases, their 2+2 cars being not quite quick enough, so that the Turbo Esprit – which is highly competitive in acceleration if not absolute top speed – is their only representative, although it does not compare in space. Ferrari need to be considered. Their 3-litre cars have not come our way for proper Autotest since the adoption of the four-valve combustion chambers, nor has the injection Boxer; the 400i is not strictly a coupé. (???? - BV)

   Concerning the cars that are listed as possible rivals, the 928S is the most obvious, from the BMW’s native country at any rate. Its bigger engine and greater horsepower for similar weight just give it the advantage in speed, and it is a fascinating car. It has ultimate handling, at a very high limit, that is a little tricky, since if it does break away at the rear, its high polar moment of inertia can make it rather a handful to catch. Its power steering is even less light than the BMW’s.

   The Lotus is of course a very different device, remarkably rapid, and blessed with immensely good manners and a very good standard of ride for its type. Its obvious limitation, especially in this company, is its space and convenience. Audi’s Quattro offers wonderful stability, and of course traction that is barely rivalled only by the rear-engined Porsches. It is not in quite the same performance league as the others, and its ultimate handling demands respect. The big Aston Martin is a larger-engined machine from a similar mould to the BMW; only tested in automatic form (although there is a manual which should match the M635 more or less), the “ordinary” Aston is beautifully mannered, with no handling quirks in spite of its size and weight – and there is always the Vantage if arguments are really to be settled. Jaguar’s XJ-S in original 5.3-litre V12 form only comes, most regrettably, in automatic form; it is still an extraordinary blend of power, handling, ride, refinement and a competitive price.

Verdict

None is perfect, of course – but there are degrees of imperfection acceptability. The Lotus disqualifies itself only because of its size, which is not comparable with the BMW. We are very fond of the Quattro, whose stability, ability to put down all of its remarkable engine performance on to the road, and practical body make it a very amiable car. It is however just a turbocharged, relatively small engine (just like the Turbo Esprit – BV), whose five-cylinder layout makes it less than refined. The big Aston has many of the BMW’s attributes; it is a similar type of car, if bigger, and its manners are excellent. But efficiency is not one of its virtues.

   Although the automatic transmission of the Jaguar may seem to put it out of contention, the price, performance and behaviour of the V12 XJ-S insist that it must be considered against the ultimate front-engined BMW. It is not quite as accelerative, although in between 70 and 110 it matches the manual BMW very closely, and its fuel economy is also very similar. Its handling up to its limit is more reliable than the BMW’s, but the German car probably has marginally better grip in optimum conditions, thanks to its wider tyres. The BMW also wins in the feel of its steering, which does not take experience to appreciate as the Jaguar’s does. For the performance-minded driver, it will certainly be the M635 CSi that scores highest of its type, with that wonderful power unit giving it such a glorious character, without the ultimate refinement of the XJ-S. We would be split between the two if it came to a decision, and would ideally prefer to take both, to suit differing moods.

Maximum speeds

Acceleration from rest (sec)