The Economy's Looking Good




In plumbing a diesel engine beneath the hood of the 2008 Audi TT TDI, the engineers in Ingolstadt are banking on a car that will appeal to both heart and head in equal measures.

Choose a TT coupe or convertible for this turbocharged diesel with its 258 pound-feet of torque and the message is much the same. That is, you're the very antithesis of that commute-hour schlub circling the block looking for a diesel pump. You're smart and you know the price of a gallon of gasoline, but you're still capable of a willful display of lead in the pencil and a brazen refusal to acknowledge that practicality has much of a say in your choice of an automobile.

Cars of this type are no novelty in Europe, where drivers are trying on the $9 gallon of gasoline for size and not much liking the fit. Alfa Romeo, BMW, Mercedes and Volvo all offer coupe and convertible models that drink from the black pump, thereby achieving great gas mileage and thus sporting plump residual values when the lease is up. The 2008 Audi TT TDI sharpens its elbows and wades into this market, and it enjoys a key advantage because it has the corner on the sports car market for diesels as long as BMW fails to fit its astonishing 282-horsepower, twin-turbo 3.0-liter diesel inline-6 into the Z4.

More's the pity, then, that the oil-burning Audi TT TDI isn't in the landing pattern for the U.S. The idea of taking the edge off TT ownership costs while packing the sort of overtaking punch more commonly expected of an old-school V8 sounds like an idea whose time has come. Too bad the Land of the Free has missed out on this particular free lunch.

Freshening Up the 2.0 TDI
The pre-drive indoctrination process at Audi's glass-and-steel corporatorium attached to Munich's Franz Josef Strauss Airport didn't take long to crank into advanced hyperbole. The 2008 Audi TT TDI coupe and roadster were hailed as "the first series production sports cars in the world to use a diesel engine as their power source." Well, perhaps the big buildup is due to the fact that the TT TDI was launched in parallel with the distinctly more commanding TTS with its turbocharged 265-hp gas-fueled engine, making the TDI appear to be the plain sister of the duo. Of course, where the TTS gets the looks, the TT TDI definitely gets the smarts.

Audi's 2.0-liter diesel has been comprehensively reengineered this year in preparation for the brave new world of diesel power, and the measures are about such things as quietness and suppressed vibration as well as power and fuel economy. The DOHC 1,968cc inline-4 features common-rail injection with piezo injectors, a measure that improves efficiency and reduces noise. The compression ratio is 16.5:1 (even in this turbocharged engine), but twin balance shafts control vibration. Even the turbo's vibration is controlled by a special damper.

The new 2.0-liter TDI produces 170 hp at 4,200 rpm, and the redline is set at 5,400 rpm. There are 258 lb-ft of torque between 1,750 rpm and 2,500 rpm.

Here is a coupe that will step to 60 mph in 7.2 seconds, and a less Neanderthal application of throttle will return a combined figure of more than 44 mpg on the European driving cycle. The TT TDI emits less carbon dioxide than a Hyundai shopping hatch, yet equals the TTS in its torque output.

Fire Up the Quattro
Since its new 2.0 TDI puts out so much torque, it's a good thing the TT has standard all-wheel drive to ensure there's plenty of traction at all times. A six-speed manual transmission is also standard equipment, both to maximize fuel economy and also to make sure everybody gets the idea that the TT TDI is a sports car.

Yet it doesn't take too long behind the wheel to find there are glitches in Audi's Matrix. While a lot of work has clearly been undertaken to reduce noise, vibration and harshness, the 2.0-liter engine's peak torque delivery is available over a surprisingly narrow rpm range between 1,750 rpm and 2,500 rpm. So this TT is not the lazy pool chair you might have expected.

The six-speed manual shift is slick and only a little wristy action on your part is enough to select the next gear, but you need to be right on top of the transmission all the time to prevent an amateurish stall or an impotent bog as you seek to deploy an optimum amount of torque. With reflection, Audi's continuously variable transmission (CVT) might have been a better driving partner, but of course noise and vibration would be an issue (not to mention durability concerns with so much torque available), plus the TT would have lost the sports-car credibility of its six-speed manual.

Diesel Performance
If you are intent on driving the TT TDI, it responds with devastating acceleration out of tighter corners. Get all the stars aligned — not to mention the turbodiesel's torque, the Bosch 8.0 stability control (fortunately with sport mode), all-wheel drive and a fairly tall final-drive ratio — and the TT TDI scuttles forward with a slightly lifeless yet undeniably effective purpose once you sweep past the corner's apex.

Like the TTS, the TT TDI features the new Haldex-engineered center differential that delivers a quicker redistribution of torque, and it goes some way toward eradicating the one-pause-two response found in the original TT. Even so, once you let the revs drop out of the sweet spot, the electronics soon begin their battle to quell stodgy understeer.

Keep the throttle pinned to the floor, and when conditions are right the coupe runs to 100 km/h (62 mph) in just 7.5 seconds on the way to a maximum of 140 mph, while the roadster gets to 100 km/h (62 mph) in 7.7 seconds on the way to 139 mph.

Clever Is Standard Equipment
Audi's new magnetic ride (you know, its magnetorheological dampers) is available as an option, but such are the compromises in front suspension calibration to accommodate the weighty diesel power plant that the difference between sport and normal damping modes is disappointingly marginal. Your money would be better spent on the leather interior package.

One other effect of the weight up front is that the electric-powered assistance to the steering system has been ramped up a notch or two, something that is thrown into sharp relief when you jump from the TTS to the TT TDI as we did. Of the two cars, the TDI's helm feels has lighter effort, yet it's more honest. It doesn't attempt to mask its assistance as false and rubbery weighting.

Like the rest of the TT range, the TDI utilizes Audi's innovative method of using aluminum and steel components in tandem, overcoming the electrolytic corrosion issues that have plagued other manufacturers that have tinkered with this approach. Some 69 percent of the body is aluminum with the other 31 percent steel, which means that this diesel TT coupe weighs in at just 3,020 pounds (dry) in coupe form.

Fuel of the Foreseeable Future?
Audi's involvement with diesel engine technology is an increasingly important aspect of the company's genome. The success of the Audi R10 TDI racecar and the near riot that accompanied the unveiling of the R8 V12 TDI prototype supercar in January at the 2008 Detroit Auto Show demonstrate a real commitment to diesel-powered performance cars. Although the 2008 Audi TT TDI is cut from humbler cloth, it has been launched nevertheless against a backdrop of senior Audi suits muttering that the future of its flagship RS sports line could well be exclusively diesel.

The 2008 Audi TT TDI represents the vanguard of a future free of spark plugs. It's a car that hangs together a little better on paper than it does in the metal, but it isn't far from being a winner.

We'll probably have to wait until diesel prices finally decline to the cost of gasoline before Audi decides that the U.S. is ready for this car. That's a shame. If you weren't quite ready to surrender to total adult responsibility just yet, a diesel coupe or convertible could have represented a tactically phased withdrawal. Rückzug durch Technik, as they might say in Germany.
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