This is Alfa's new 140bhp, 16-valve JTD engine, available in UK-bound 147s from next June; it will also slip under the bonnet of the 156. The eight-valve, 115bhp edition gets here in March, a bafflingly long wait given that it has been in European mainland 147s since the range's launch, but there we are. The 156 gets a new 20-valve, 170bhp version of its five-cylinder, 2.4-litre JTD motor in June, too. So there's lots of oil-burning action at the Societa Anonima Lombarda Fabbrica Automobili.

Alfa Romeo was the first car manufacturer to offer a common-rail diesel engine in Europe, just ahead of its Fiat associate and the Peugeot-Citroί¿½n group. Its offerings haven't been the most frugal of diesels, but they have been among the more invigorating. That's relatively easy with a five-pot because it can't help but sound interesting. But a four?

Massai makes promising claims for the new 16v motor, such as more torque throughout the speed range, less of a drop-off after the peak, and a steeper rise to that peak. More like a petrol engine, in other words, albeit shifted a couple of thousand or so rpm down the tachometer scale. Peak torque from the 1.9-litre unit is 225lb ft - fractionally under a Golf TDI 130's 228lb ft, but more than a 147 GTA or 156 GTA can muster.

The better breathing of the 16-valve head, with its twin cams and low-friction, roller-finger rockers, plays a part here. So does the new variable-geometry turbocharger. The key, however, is the Multijet injection. Pilot injection, a small squirt preceding the main spray, is usual in direct-injection diesels. It makes combustion pressure rise more gently, reducing both the diesel clatter and the exhaust smoke, while increasing efficiency. But this new JTD delivers not just two but up to four squirts, depending on conditions: two small ones before the main one, followed by a small after-squirt. Injection pressure rises from 1300 to 1400bar, too.

The benefits are as before, but greater. They're easy to exploit, too, thanks to a particularly sweet-shifting six-speed gearbox that makes the most of a diesel's relatively restricted power band (this one dies at 4800rpm) and ample torque. This 147 cruises with loping ease at illegal speeds, bringing on the worry common in the best new diesels that you often don't realise just how fast you're going (honest, officer). Given the chance, it will touch 60mph from a standstill in under nine seconds and torque itself onwards to 128mph, but those figures simply don't do justice to the effortless overtaking ability.

This 147 is pretty quiet, too, thanks to almost-complete engine encapsulation to help damp down the diesel clatter. Open the bonnet and you'll see a virtual engine, not a real one: there's a big plastic top cover, with a vague representation of four non-specific objects set in the imitation aluminium, while fabric covers fill in the gaps right to the engine bay's edge.

But does it sound like an Alfa engine should? It would be mighty impressive if it did, but frankly diesel-ness outstrips Alfa-ness. There's a pleasing exhaust resonance, though, as the turbo spools up and the 147 surges onwards, which makes up for the initial response lag and the soft accelerator response. (Try an AMG C30 CDI to see how that should be done.)

Now, here's an odd thing. This JTD was revealed to us at the same time as the GTA, and I spent a while chasing that hottest 147 along some sinuous Italian roads. Was keeping up a problem? It was not, unless the road opened right out. The easy thrust had a lot to do with this, but so did the ride and the joyously understeer-resistant handling.

Clearly the JTD's 195/60 VR15 tyres were never going to grip like the GTA's 225/45 ZR17s, but their greater slip angles, and the suspension's surprising suppleness, somehow made it easier to feel what was happening underfoot and where the grip limits lay. And that's despite steering which, while very quick, was a bit short on turn-in feedback.

The moral? There's more than one route to a rapid and rewarding real-world drive. Oh yes, and the figures say the JTD averages 47.9mpg. Now, if only it could be made to sound like the GTA.