Sunday, 29 April 2012

The Speed of Sound

The new Mercedes-Benz SLK250 CDI has more torque than its V6 petrol sibling despite two less cylinders, and is only a tenth slower to 62 than the similarly priced SLK250 petrol. Yet according to Stuttgart, the oil burning SLK returns over 56mpg on the combined cycle and emits less CO2 than the most polar bear friendly A-Class. It’s by far the most efficient SLK ever.

So why couldn’t I get on with it? Well, it’s all to do with the noise. The SLK250 CDI’s pace is unquestionable. It fires off the line with maximum twist from just 1,600rpm and before you know it, you’re doing naughty speeds and glancing in your mirrors like a paranoid with a dodgy tick, hoping the rozzers aren’t watching your every move.

But, as I found out, just because your diesel sports car can mix it with the big boys in a straight line doesn’t make it an intoxicating drive. Diesel engines are all about keeping cash in your pocket – even if it takes 10,000 miles for their premium over petrol models to be nullified. And so, to expect a spine tingling soundtrack from a motor with ‘third generation, common-rail, direct fuel injection’ is as foolhardy as expecting it to redline at 7,000rpm. It’s just not going to happen.

Mercedes’ 250 CDI engine is a lightweight, torque heavyweight and its inclusion in the SLK range challenges people’s perceptions of what a sports car can and can’t be. But it’s a task too big even for the truly superb, four-cylinder biturbo motor.

A sports car allows you to bask in the texture of an engine’s voice. Roof down motoring doesn’t get any better than when your every move is backed by the rich sound of pure mechanical opera. But on the occasions when I did hang onto the SLK250 CDI’s gears and eek out every last drop of performance, I instantly regretted it because the rugged, diesely drone was unescapable. Worse still, when the SLK’s roof is down you hear everything a pedestrian would, which really does make you think twice about ‘dropping the hammer’ again. That’s just not how a sports car should make you feel.

The SLK’s four-pot and V6 petrols produce a sound that’ll have people spinning on the spot and you grinning like a mentalist. All the diesel engine does is let people know you’re as bothered about fuel economy as style – and that’s just not very cool, is it?

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