Buyers can opt for one of four powerplants in the Infiniti Q50; the bulk of sales will no doubt be attributed to a Mercedes-derived 2.1-litre turbodiesel. There's also a 3.5-litre petrol-electric hybrid for those seeking a more serene experience backed up by some serious punch, while the petrol range is punctuated by 2.0- and 3.0-litre units.

Infiniti’s first four-cylinder diesel engine, despite its impressive origins, has not entered at the top of its class. There’s more to noise intrusion than simple numbers on a noise meter, and here’s a case in point.

Nic Cackett

Nic Cackett

Road tester
The Infiniti's diesel engine could be quieter, and its gearbox quicker

The Q50 fires to an idle that registered 1dB less on our meter than a 320d did, but it seems louder and more irritating because of a prevalence of diesel rattle from which the powertrain, except at motorway speeds, never shakes loose.

It’s fine in low-throttle operations. Step-off is easily measured and the seven-speed automatic gearbox shifts smoothly enough around town and at a cruise. Expect more, though, and you’re likely to be disappointed. From rest to 60mph, the Q50 lags behind not just the 320d (8.7sec versus 7.7sec) but also the C 220 d (albeit by only a tenth).

We mention these figures not because 0-60mph sprints are regular features of a compact executive saloon driver’s day, but because they are a handy benchmark. We could just as easily have picked 30-70mph, through which speeds the 320d is 1.3sec faster than the Q50 (8.7sec).

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Ask more of the Infiniti’s performance than leisurely cruising and you’ll not only find that the engine sounds strained towards the uppermost reaches of the rev band, but also that the gearbox is reluctant to shift down of its own accord, and stubborn if you ask for it.

However, the Q50 did return admirable economy in our hands. Its touring figure (59.2mpg) was a touch better than we returned in a 320d and its 45.5mpg average was superior to the BMW’s 41.6mpg.

It was slightly damp when we figured the diesel Q50 – not sufficiently so to affect acceleration from rest, but enough to account for the fact that, on greasy asphalt with some rubber laid on it, the Q50 braked no better than on good, clean, wet asphalt. Both figures are good, though, and the Q50’s stoppers gave no indication of fade.

On the hybrid front, there's much of note. It offers buyers a sensible blend of pace, economy and performance, while proving smooth and effective in its operation. Off the line the Q50 hybrid moves away effortlessly, with the electrified powertrain permitting the V6 to shut off regularly and for extended periods. It's not difficult to eke over 40mpg out the Q50 hybrid, according to the trip computer at least.

Get into the country and you'll see that figure drop to the 30s, but the tradeoff is a fast-feeling saloon with an obedient and unobtrusive transmission. The V6 is suitably evocative when it revs, but over-active safety systems can curtail any fun that you might find. The hybrid's brake pedal could do with being more consistent, too.

It's hard to deny the impressive quoted figures, though; Infiniti says the hybrid will do 0-62mph in 5.1sec and reach 155mph. It'll do that, however, yet still be capable of potentially averaging 45.6mpg and emitting a reasonable 144g/km of CO2.

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