WHEN you consider the success of BMW over the past four decades, it is easy to forget that the company almost went broke in the 1960s.

What saved the Bavarian manufacturer was its successful redefinition of business-class sports motoring, essentially filling a niche vacated by Jaguar.

While the 1500 sedan is the single vehicle credited with saving the marque, it was the sporty models such as the 2002 and later the 323i that differentiated BMW in a crowded market.

It is a long way from the 1500 sedan to the new 650i convertible but the DNA is unmistakable and that old ‘ultimate driving machine’ theme from the 1970s and 1980s is completely relevant to this second 6 Series drop-top.

Engines have always been crucial to the BMW brand, as signified by the famous four-cylinder building in Münich which has been BMW headquarters since the early 1970s.

The twin-turbocharged 32-valve 4.4-litre V8 beneath the smooth prow of the 650i Convertible shows how far the marque has moved from its reliance on sporty four-cylinder units.

The V8 engines introduced in the 1990s had good top-end power in true BMW tradition but lacked the low-rpm torque Australians expected of this configuration. But two decades on the change has been dramatic and the 650i’s engine combines the best of all V8 worlds.

Extraordinarily, and thanks largely to the use of two smaller turbochargers, this 4.4-litre unit offers its maximum torque of 600Nm right through from just 1750 to 4500rom.

Peak power is 300kW, available from 5500 to 6400rpm. Zero to 100km/h is said to take five seconds flat - Ferrari territory not so many years ago.

The eight-speed torque converter automatic transmission is exemplary for its smoothness and an alacrity off the mark rarely found in the DSG-style gearboxes which are quickly displacing this older type.

Ratios can be selected manually via the paddle shifts or the elegant, uniquely BMW-style floorshift, the tactility of which helps to make driving the 640i convertible so rewarding.

There is no doubt that so many ratios contribute to the acceleration as well as to the remarkable fuel economy.

The official combined figure is 10.7 litres per 100 kilometres but GoAuto saw mid-sevens in open-road usage with no special lightness of the right foot. The 650i convertible also features brake energy regeneration and auto idle-stop.

This tester especially hates the body flexing which was once endemic to open-roofed vehicles and is still the scourge of many cheaper models.

Only some Ferraris and Porsches deliver a comparable sense of rigidity. Even the latest Mercedes E-class cabriolet cannot equal the BMW’s ability to shrug off ridges in the road or that crucial test of turning into a steep driveway where you feel many convertibles twisting slightly, front to rear. You almost forget that it has a fabric roof.

Doubtless the stiffness of the body plays a role in the 650i’s flawless dynamics. Adaptive Drive is standard. Without indulging the BMW plethora of acronyms, this feature eliminates bodyroll and gives the driver four separate driving modes with further choices available through the i-Drive menu.

But the car is so good, one wonders how much this really adds. Even in ‘Comfort’, the softest of the four suspension settings, it turns into corners like a sportscar. There’s little need to look beyond ‘Normal’, in which mode the ride is still amazingly supple considering that this BMW has 19-inch wheels and run-flat tyres (notorious until recently for adding harshness).

GoAuto oscillated between ‘Normal’ and the attack-dog ‘Sport+’ mode. In the latter a physical flap inside each rear muffler opens at lower rpm to deliver the kind of sensational V8 exhaust note that would never get by the drive-by noise legislation.

Surprisingly, in ‘Sport+’ there is still some comfort to the ride and the only reason you would switch back to a less aggressive setting is that the car is so good in any of the four modes.

Living with the car brought a change in attitude from the press launch, where the 650i spent a lot of time in ‘Sport+’ Mostly, on a day to day basis, ‘Normal’ – the default setting – ticks the boxes.

Run-flat tyres have previously been criticised and another less than ideal aspect of the dynamics of many recent BMWs has been the numbness of the electric steering.

This, too, has been resolved on the 650i, which delivers meaty steering feel with great directness.

Many critics will prefer the design of this new sporting flagship to the highly individual and somewhat confronting 2004 model. Key styling themes have been taken from the world of upmarket power boats and the final effect is of thorough integration and a smoothness lacking in its predecessor.

The 6 Series is not as individualistic as its predecessor but neither does it succumb to the blandness of the current 5 Series range: call it a happy medium between the extremes of the Bangle School and the characterless appearance of the current Five.

It is also better packaged than the previous model with an extra two inches in the wheelbase and a similar increase in width for more interior room.

The multi-layered fabric roof (available in three colours) is a marvel in engineering. When erected, the 650i is barely noisier than a luxury sedan, and takes just 19 seconds to drop and 24 to raise, both of which can be done at road speeds of up to 40km/h.

You really wonder why for any reason other than torsional stiffness any manufacturer would choose metal (with all that sacrifice of simplicity and space that entails). It seems like the most intelligent way to develop a convertible: make a really stiff structure, add a lightweight fabric roof.

Our test vehicle featured the expensive Nappa leather dash option ($3000) complete with piping ($500 on top of the $3000). This confers some additional elegance to a standard vehicle that does not disappoint in this area, a case perhaps of gilding the lily.

But the no extra cost American Oak wood trim is a joyous thing. The Dakota leather upholstery is soft, plush and should prove durable (BMW having learnt harsh lessons about the Australian sun when it sold 735i Executives in the mid-1980s trimmed with gorgeous buffalo hide).

You expect a high level of specification in a vehicle costing a quarter of a million and the 650i convertible delivers it.

BMW’s Professional Navigation system is excellent and the rear-view camera proves most helpful when trying to look back over that high-piled hood (thank goodness for something to criticise!).

You can switch the head-up display off but probably won’t. You can display your emails via Bluetooth. You even get TV. Bi-Xenon lights are included in the deal. The adaptive cruise control works better than many such systems and is switchable.

Heated and ventilated front seats obviate the need for the wizardy found in the latest Mercedes drop-tops (although these might come into their own in a Scandinavian winter).

Amazingly, you no longer pay extra for the metallic paint schemes which dominate the colour chart.

In summary, the 650i Convertible is one of the all-time great BMWs, embodying all the marque’s finest qualities with few irritations.

Its striking appearance is not compromised by idiosyncrasy and its sports appeal does not come at the expense of lavish comfort.