BMW 640d vs BMW M635 CSi: 2011 twin test

Believe it or not, the new diesel version of the BMW 6 Series is predicted to account for an incredible 93 per cent of the model’s UK sales. The company expects the 640d to be the most successful version yet, and it’s easy to see why.

Here’s a car that can sprint from 0-60mph in only 5.4 seconds, yet return claimed economy of up to 51.4mpg. Low emissions and a four-seater interior packed with gadgets do the rest.

The newcomer is in a class of one, because none of its rivals offers the option of a diesel engine. As a result, nothing on sale today comes close to matching its mixture of talents, so we decided to look to the past instead.

In 1986, the BMW M635 CSi set the benchmark for luxury GT performance cars. It was fitted with the same 3.5-litre engine as the legendary M1 supercar and its combination of blistering pace, rear-wheel-drive handling, muscular styling and cosseting comfort gave it cult appeal. And after 25 years, it has become a bona-fide classic.

The new diesel 6 Series may be faster and more economical than its potent petrol ancestor, but can it really live up to the legend?

Verdict

An impressive debut – the 640d’s new diesel engine, long-haul comfort and luxurious cabin all make an impression. Not only is it faster, cheaper to run and nearly twice as economical as the M635 CSi, it also has a dazzling array of technology and safety equipment. It’s no lightweight, yet with the optional Adaptive Drive dynamics, it’s a remarkable machine.

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But so is the M635 CSi. No matter how good the 640d’s engine is, it can’t match the spine-tingling soundtrack and pin-sharp responses of the old timer’s straight-six powerplant. Sure, its handling isn’t up to modern standards, but the M635 CSi is utterly engaging to drive.

Which is better? As they’re from different eras, direct comparisons are pointless, but what the 640d does demonstrate is how much progress has been made in the last 25 years. We’d love to have both cars on our driveway.

First place: BMW 640d

The first thing that strikes you about the new 640d is its size. At 4,894mm long, the BMW is a seriously big car. Its long bonnet, 5 Series-style grille and sharp lights make it look incredibly sleek. It doesn’t have the distinctive, shark-nosed lines of the original, but it’s still a very smart design.

In M Sport spec, you get 19-inch alloy wheels, black brake calipers, a diffuser-style rear bumper, plus sports sills. Sitting behind the chunky wheel, the sweeping lines of the dashboard and centre console envelop you – it’s much more intimate than its ancestor.

There’s a reassuring solidity to the switchgear and controls, and the standard 10.2-inch sat nav screen and iDrive controller are easy to use. Mobile phone signals are employed to provide real-time traffic information, which proves to be much more accurate than rival systems. Similar technology is already available in off-the-shelf portable sat-navs, but it’s the first time it has been installed in an integrated factory-fit unit.

Our test car was also fitted with optional comfort front seats (£1,485) with Nappa leather, which provide a vast range of adjustment – if you can’t get comfortable sitting in these, you must be doing something wrong.

If you keep exploring the options list, you can add lots more interesting interior kit, including Park Assist (£570), surround-view cameras (£530) DAB digital radio (£315) and even night vision cameras (£1,535) or a head-up display (£980). But with plenty of standard equipment, there’s no need to go mad on extras.

It’s out on the road where the 640d really impresses, as the new twin-turbo diesel provides effortless performance. With lots of traction, 630Nm of torque from only 1,500rpm and a smooth-shifting eight-speed automatic gearbox, the BMW sprinted from 0-60mph in only 5.4 seconds at the track.

In-gear acceleration figures are even more impressive, and show the 640d is fast enough to keep supercars honest. Only an average showing in our braking tests let it down.

Straight-line performance is only part of the story, though, because the 6 Series has always been a rewarding driver’s car.

Opt for the £3,400 Adaptive Drive package and you won’t be disappointed. It fine-tunes the suspension, steering, throttle and gearbox settings to suit each of the five driving modes. Sport and Sport+ give the sharpest responses, but ride comfort suffers.

The Comfort setting is the best compromise, as it suits the lazy nature of the car’s power delivery. Drivers who crave even more precision should also consider the £1,220 optional Integral Active Steering package.

It adds rear-wheel steering to the mix to improve manoeuvrability around town and agility at higher speeds. But even without it, the BMW steers with accuracy and confidence.

For all its grip and pace, this car is essentially about effortless performance and the ability to cover vast distances with minimal fuss and interruption.

There are definitely more exciting ways of getting from A to B, but no other luxury coupé will do the job as efficiently and quickly as the new 640d Coupe.

Second place: BMW M635 CSi

The BMW M635 CSi has cemented its place in the automotive history books. It offered peerless performance for its day, thanks to sharing an engine with the potent M1 supercar. And as the first practical M car, it kick-started the company’s now-famous Motorsport Division into life.

From the outside, it’s clear which decade the M635 CSi belongs to, as the chrome trim, relatively small alloys and large glass area all hark back to another era. But it’s still a striking sight, even parked next to its modern cousin. The shark nose, long bonnet and rubber boot spoiler all hint at its significant potential.

Up front, the four individual headlamps are nowhere near as effective as the hi-tech xenon units on the 640d, but they give the car a very purposeful look.

From behind the wheel, the CSi is very easy to place on the road, as the driver has a great view out. Its thin A-pillars contrast sharply with their thick counterparts on the new car.

The cabin also betrays its old age in other areas. The chunky buttons, haphazard layout and thin-rimmed steering wheel will all be unfamiliar to drivers of modern cars. Compared to the luxurious trim of the 640d, it’s functional, but the sparing use of M badging inside is refreshing.

Despite offering electric adjustment, the M635 CSi’s supportive seats can’t match the 640d’s for comfort. Offset pedals and a heavy clutch also belong in the past. The sculpted rear seats look great and the rear side windows open electrically, unlike the new car’s fixed ones.

Another area where the old timer beats the newcomer is the sound of its engine. The straight-six bursts into life with a wonderful burble. The five-speed manual gearbox has a positive action, and the throttle response is much crisper than the 640d’s. And while its diesel counterpart has a smooth, linear power delivery, the 3.5-litre petrol in the CSi howls demonically as performance perks up at the top of the rev range.

There’s nothing wrong with the direct steering, and turn-in is sharp. There’s plenty of front-end grip, too, but while body roll is tightly controlled by eighties standards, there’s plenty of it in evidence when compared to the modern car.

The trade-off is the kind of ride quality that many new car drivers can only dream of. And driving the M635 CSi is an intoxicating experience. The new 640d runs rings around the M car dynamically, but the 25-year-old model is far more involving behind the wheel.

One of the biggest differences between these BMWs comes to light when you look at efficiency. As the modern car is much faster and heavier than its ancestor, it’s logical to assume that it will be thirstier, too. But you’d be wrong.

According to BMW’s figures, the M635 will do 29.1mpg, but the 640d is capable of 51.4mpg. As a result, while the eighties model can manage 448 miles between fills of its big 70-litre tank, the modern diesel can cover 791 miles. Now that’s what you call progress...