Diesel Technology For The Future - Future Present

Until recently, diesel was for trucks and tractors. There'd be more chance of Malibu Beach freezing over than spying an oil-burner on these pages. However, times are changing.

Exorbitant fuel prices forced Europeans behind the wheel of diesels in record numbers, and they now account for half of all new car sales in most of Europe.

The manufacturers have played their part by investing heavily in diesel technology to ensure their products are now more tempting than ever. You can forget about the noisy, smelly, smoky diesels of old and revel in the torque-laden experience of driving a modern, European diesel automobile.

The technological leap forward means some of the latest diesels are borderline sports cars that can top 40mpg. Audi and Peugeot have even taken them racing at the highest level, with more sure to follow. And it won't be long before the first diesel-powered supercar hits the streets.

It's diesel economy and longevity that makes the cars so appealing. The latest Mini diesel reportedly returns a stunning 76mpg on the freeway. And while it's unlikely to reach US shores, it's easy to see how the world's oil supply would be preserved if people stopped driving SUVs and switched to small diesels for their daily commute.

The ponderous, smoke-belching diesels of yesteryear are forgotten, thanks to innovations like Common Rail injection and Piezo crystal injectors that have raised injection pressure beyond 2000bar, helping to improve the efficiency of the fuel burn and thus reducing emissions and noise. Low-pressure turbos have also proved a revelation for the diesel industry, and marrying these two technologies brings diesels new respectability.

Porsche may have taken the credit for using Variable Turbine Geometry on its 911 Turbo, but this concept is commonplace on turbo-diesels.

And the advances keep coming in the form of Ecotec, a new particulate filtration system that, along with low-sulphur diesel, has opened the door once again for vehicle sales across the US. And with a new market the size of North America, there will be bloodshed between the manufacturers. A new power struggle is coming, and it's going to be good for the consumer.

The bi-turbo, 286hp BMW 335d/535d, the Mercedes E320 CDI and the VW Golf TDI have rightly taken their place among the pantheons of motoring legends in Europe, thanks to their ability to cruise past gas stations and still put a smile on the owners' face with respectable performance.

But horsepower is only half the story. Diesels thrive on stupendous amount of torque, generating most of it low down the rev range.

Of the latest crop, BMW's 335d and 535d are among the very best available. Their three-liter, six-cylinder motor uses sequential turbos; a small one runs from idle to about 1500rpm, then a larger one kicks in and they run together to about 2500rpm, at which point the smaller one shuts off. It's taken the art of diesel engines to a new level, with peak torque of 430 lb-ft coming at an insane 1750rpm. So a lazy run along the highway can be transformed into a balls-out overtaking move with a twitch of the right foot.

To put that into perspective, it's about the same amount of torque that a Porsche 996 Turbo has, so the performance couldn't be described as dull. In the real world, low-speed torque beats high-revving power on corner exits and when overtaking. With this kind of grunt, the 335d can hit 62mph in 6.1sec and will comfortably hit the 155mph limiter.

It's time to adjust our perception of diesel, because these cars offer deceptive speed, where engine noise barely intrudes into the cabin. Yet the twin-turbo 3.0 can't be ordered with a manual transmission because BMW doesn't have one in the lineup that can handle it.