DETROIT – On one of the city’s fastest freeways, the late-model Honda Civic Si isn’t quite blocking traffic, thrumming along in the leftmost of four lanes at 85 mph (136 km/h) or so.

But it’s all that stands between the diesel-engined BMW 330d and our last fix of “performance diesel.”

The 20-something driver sees us coming, and as he grudgingly slides right, we tromp the accelerator. By the time we’re momentarily beside the Civic, we’ve already surged past 110 mph (177 km/h) – yet the shock wave of torque is still on the rise.

Even at that velocity, our premium performance sedan may be getting better fuel economy than the cruising economy car.

The BMW 330d, currently available only in Europe, is the latest generation of BMW’s iconic sport sedan stuffed with three liters of state-of-the-art, inline 6-cyl. turbodiesel. The mere fact this package exists is the final proof anyone needs that diesel’s day has come.

Europe loves BMWs, but it also loves diesels to the tune of about 50% of the new-vehicle market.

So BMW had to find a way to serve the diesel demand without compromising the decades of work it’s lavished on burnishing its “Ultimate Driving Machine” heritage. The result is the magnificent 3L inline 6-cyl. turbodiesel that can’t come here fast enough.

This particular car is not available for sale in the U.S. It is on loan courtesy of Honeywell Tubo Technologies, maker of the excellent variable-geometry turbocharger that is so integral to the engine’s power and performance. Originally launched for the larger and much heavier 7-Series flagship, BMW says this engine is the most powerful diesel ever to be fitted in a 3-Series.

European power figures are 231 hp at 4,000 rpm and a shattering 369 lb.-ft. (500 Nm) of torque, thundering its all at just 1,750 rpm.

In addition to the sophisticated Garrett turbo, these numbers are achieved thanks to Robert Bosch GmbH common-rail, direct-injection fueling at 23,300 psi (1,600 bar). There are as many as four distinct injection “events” per combustion stroke and 32-bit engine management with a remarkable 6,000 distinct control “maps.”

BMW brass wasn’t fearful of a diesel eroding its jealously guarded performance image largely for one reason: This new-generation diesel will whip just about any like-sized gasoline powerplant.

Anyone thinking 231 hp is too meager for BMW’s iconic sport sedan should remember that until the heavily revised N54 gasoline inline 6-cyl. was launched last year, the 3’s highest-horsepower gasoline engine generated just 4 hp more than the 3L turbodiesel. Moreover, the 3L turbodiesel churns out 65% more torque than the new N54 – currently the 3-Series’ top engine in the U.S.

Doubters will be further disarmed either by the 6.7 seconds it takes to scamper to 62 mph (100 km/h) or the 155 mph (249 km/h) top speed. Judging by the hilariously short distances required to burst to, say, 130 mph (209 km/h), the 330d feels it could show you 155 mph just about anytime you want to see it. The torque is just that glorious.

All this, of course, on top of the 36 mpg (6.5 L/100 km) BMW claims for the European combined driving cycle.

The 330d’s fuel economy meter showed about 38 mpg (6.2 L/100 km) in 85-mph freeway driving. A driver might get that from a Toyota Prius, but certainly won’t get to 60 mph (96 km/h) in 6.7 seconds in Toyota’s whiny hybrid-electric vehicle.

In the 330d, this marvelous meld of performance and economy isn’t hurt by the M Sport option package, which includes a tighter suspension, subtle-but-effective bodywork enhancement and first-class sport seats and steering wheel.

The package includes a short-throw shifter for the 6-speed manual – the only transmission available. In truth, that short-shift kit should be standard equipment for every BMW manual.

The only downside is a taste of nose-heaviness that’s inevitable with an iron-block diesel up front. The turn-in and steering response are noticeably – although not disconcertingly – more ponderous than expected from BMW’s compact sport sedan.

Most drivers will agree it’s not a deal-breaker, just a matter of acclimation. Perhaps it could be mitigated, however, if BMW would give up its preference for time-honored grey iron for the engine block and adopt the lighter, purportedly stronger compacted graphite iron (CGI) favored by rival Volkswagen Group.

Regardless of its minor impact on handling acuity, BMW’s brilliant 3L DOHC I-6 turbodiesel is one of the best arguments yet for new-age diesel power. The 330d’s superb on-the-road performance easily surpasses that of its gasoline-engine counterpart.

Factor in no less than 25% better fuel economy, and the 330d is a pro-diesel argument that’s hard to ignore – regardless of the inevitable price premium such a lavish diesel (and its requisite 50-state exhaust-aftertreatment system) is likely to demand.

bvisnic@wardsauto.com