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.