Twin sequential turbochargers? They’re just so now. Here we’re sampling the affordable end of this new wave, in a Vauxhall Vectra. A diesel Vectra in fact, its 1.9-litre oil-burner boosted by a small, high-pressure turbocharger that provides boost to 1800rpm, and a bigger, light-pressure unit that takes over between 1800rpm and 3600rpm.
In practice, the two overlap for a seamless stream of torque, of which a fat 332lb ft gush is available between 1400 and 3600rpm.
But before we tell you how fast that makes a Vectra go, here’s the reason for those twin KKK turbos. A single blower can yield the same peak power of 212bhp but leaves a large hole in the lower end of the torque curve, precisely where the engine operates most often.
Modern turbodiesels, including Vauxhall’s current 150bhp 1.9 CDTi Ecotec, run with a blower sized for compromise between strong mid-range urge – this same motor musters 232lb ft of torque – and ultimate power. Run large and small in tandem and you’ll have the best of both worlds, and still return 47.0mpg on the combined cycle, an amazingly small drop from the 150bhp motor’s 47.9mpg.
And you certainly get some thrust. Vauxhall claims 6.0 seconds to 60mph, while top speed is reined in to 155mph. Remember, we’re talking about a diesel here. Vauxhall showed this car as a concept, painted a vivid blue, at the Birmingham motor show, and we got to try it, admittedly in far-from-finished form, on an airstrip near Frankfurt.
The trouble with wide open spaces like this is that they don’t really provide an accurate sense of speed and acceleration – or don’t until you reach a bend suddenly enough to provoke the Vectra’s understeer-countering ESP.
That was enough to remind us that while the Vectra is rather good at taking corners at considerable speeds, the slightly numb steering of this unfinished car make this an activity that you won’t be pursuing for the hell of it. But the finished article, out early in 2006, will be badged VXR, which will signal the ministrations of Lotus. So there’s a fair chance that this Vectra might be an entertainer.
It will also be more powerful than this car, which was running with 292lb ft of torque rather than 332lb ft to preserve its gearbox – the production version gets a tougher transmission. It will also get a smaller low-rev turbo to sharpen low-rev throttle response, as there was some lag despite the elaborate set-up, and the strategy for blending the efforts of the blowers will be refined, too, the need for which I discovered by opening the glovebox.
Lurking inside was a boost gauge, and while it was a challenge to stare at that, steer the car, deploy full throttle and not crash, I can report that there is indeed a brief dip in pressure part way through the rev range, though it wasn’t very noticeable on the road.
So there’s more development to come, but it’s hard to see how the finished package can fail to impress in terms of performance and economy. With the right kind of fettling under the arches, the diesel Vectra VXR could turn out to be as startling as the blue interior of the concept. And all for around £22,000.