This is like one of those scenes that breaks the spell of an otherwise compelling novel, like normally car-savvy Iain Banks writing about a Peugeot 209 in The Crow Road, or Arthur Hailey describing in Wheels how the secret prototype screams up to 85mph. Are we witnessing some mistake? No, there is no mistake. Instead there is a future, and it's very probably diesel-powered.

But can diesel ever power a true performance car? Can it really deliver evoness? As petrol engines become ever softer-edged under the strictures of Euro 4 emission regs and drive-by-wire throttles, it's the diesel that emerges from the shadows on a wave of that new performance provider: torque. BMW's latest 320d delivers 243lb ft of it from just two litres. And as for the 330d, how does 288lb ft grab you? Quite hard, when transmitted to your body via a driving seat.

And of course there's the fuel economy, although this is less of a draw here in the UK than it is elsewhere in Europe thanks to the cost of the fuel (by far the EU's highest) and a tax penalty both for the tax disc and company car tax. That penalty is small, though, and even against these odds the diesel makes monetary sense provided the car doesn't cost too much more in the first place. But that is just one of the balances to be struck. In this test, we're balancing another: power.

The green 330d Touring you see here, the car with the 4600rpm upshift point, delivers 184bhp as well as that torque mountain. The silver 325i Touring can generate a little more power at 192bhp, but its torque is 'just' 181lb ft. So, which will be quicker? And which will provide the richer driving experience?

With similar power, the two Tourings should deliver similar ultimate pace. So, to cut to the chase of how different the delivery of that pace might be, we're using five-speed automatic versions of both cars. That reduces variations in driving technique, and lets us compare the change-up strategies.

So we're lined up on a straight at the Bedford Autodrome, John Barker and I, and the drag race is about to begin. We count down in sync, left feet hard on brake pedals, right feed hard on accelerators, stalling the torque converters for no more than a couple of seconds before left-foot-off and blast-off. Traction control systems and air-conditioning are also off.

The 325i launches itself into the lead, the 330d still some way off full turbo boost because the engine hasn't been revving high enough. Then the diesel torque comes flooding in and a second after standstill it's matching the 325i's now-declining acceleration rate. In another half-second it's pulling harder than the 325i and will do so up to 30mph. That's where the graphs intersect again, and from that point on the two cars pile on speed at a near-identical rate.

On the track, this means that the 330d hauls in the 325i and they stay within a length of each other to 60mph. The 325i then eases ahead a little, but as 100mph approaches the 330d is gaining ground again as the torque continues its flood. Look at the acceleration table, and you'll see how closely matched the acceleration rates are. If it wasn't for the 330d's slight launch delay, if it had reached 30mph in the same time as the 325i (whose 2.96sec time is pretty special for an automatic), then the 330d would have had its nose in front all the way to 60mph.

Which means what, exactly, out in the real world of real roads? The 325i was upshifting at 6300rpm, the 330d at 4600rpm ΂- or less, in the case of the first-to-second change. One was driven by the power that high revs produce, the other by the more relaxed power that goes with ample torque.

So, three litres of common-rail, intercooled turbodiesel gets you to your destination just as quickly, but rather more discreetly and less stressfully than 2.5 litres of naturally aspirated, variably valve-timed petrol engine.

But there's bad stress, and there's exciting stress. The 325i does all you expect a BMW to do, its engine spinning with the usual creamy, lightweight note, all preconceptions confirmed including the hunch that it's going to spend a lot of time in the lower gears when you're pressing on. It's a busy soundtrack, but it will lift you up not wear you down. Exciting? Not especially.

Maybe it's torque that adds excitement. So we move to the 330d, and real pulling power. This is more fun; press the accelerator and this BMW just thrusts forward, usually without bothering to change down, because there's no need and the gearbox knows it. And if it does change down, or you do it yourself with the Steptronic tip-shift, it's smoother than in the 325i. More urge, less effort. And here's the clincher; the engine is almost as smooth as the 325i's. It emits hardly any diesel rattle, and it has a voice. A proper note; deep, authoritative, six-cylinderish. This is not just a great diesel. It's a great engine.

And the downsides? The 330d costs ΂£2875 more than the 325i (never mind the test car's optional Sport pack), although it's on a level with a 330i. It isn't especially economical if driven with gusto: 28.5mpg on test against the 325i's 26.4. And you might expect its heavier engine to dull the handling, although in reality you can barely feel the difference.

But this isn't about buying a diesel to save money and suffer pain. It's about buying a diesel because you'll have more fun with it. This is the future. Don't worry. It'll be fine.