Diesel Street Cred: Mean and Green

The adrenal glands are working overtime. We've drawn the ticket that will make us the first person outside of Audi's own development team to drive the awesome 2008 Audi R8 TDI Le Mans Concept. As in, first person in the world.

This is the midengine diesel-powered sports car concept that drew drooling crowds at the 2008 Detroit Auto Show, where it made its international debut as the Audi R8 V12 TDI Concept.

It drew crowds again this month when its name became the Le Mans Concept for the 2008 Geneva Auto Show, where it pretended to be a different diesel sports car with a new coat of red paint covering the hide of matte silver it wore in Motown.

Now that this car has a real name, everyone is hoping that Audi is planning on series production. Company insiders won't deny it, but they're not very encouraging, either. The 6.0-liter, 60-degree V12 diesel is a little longer than the R8's 4.2-liter V8 gasoline engine, and it's still too big for this car's engine bay. This issue is being worked on, but there's also talk of using Audi's 4.2-liter V8 diesel.

Big Tease
Opportunity didn't live up to anticipation, as our first drive turned out to be an epic tease.

This two-seater is a hand-built concept, you see. The only one in the universe, Audi assures us. To protect it there were limits — lots of them.

The drive took place Friday morning on a long-abandoned landing strip, a roughly 500-yard stretch of cracked and pebble-strewn runway in central Florida just on the other side of the racing circuit where the Audi R10 diesel was trying to win the 12 Hours of Sebring.

There were no twisties to challenge the Quattro all-wheel-drive system, no elevations to test the V12 diesel's pulling power. Instead we had just flat concrete that had been a training strip for Boeing B-17 bombers some 62 years ago but now had grass growing up through the cracks.

We couldn't even use the flat straightaway for what the motoring gods would surely have wanted us to attempt. "Please try not to drive at more than 35 or 40 mph," project manager Uwe Haller asked.

Don't Ding It
Haller had spent the foggy, early-morning hours walking the strip and picking up rocks and nails. "Lots of them," he said with a wince. But there were more out there and Heller didn't want speeding wheels to kick up anything that would damage the paint, or the undercarriage, or the polycarbonate (and not street-legal) windshield and see-through roof panels.

For the same reasons, no full-power launches and no spinning tires — no attempts to see if all that torque could overpower the traction control. In fact, all that torque had been dialed back for the inaugural test-drive session to just 443 pound-feet, only 60 percent of the V12 engine's capability.

And by the way, we got the car for a mere 30 minutes, and part of that time was devoured by a forced halt when a vent tube started dribbling diesel fuel into the forward corner of the engine bay (just behind the driver seat) because a safety cap had not been properly installed. Ah, the joys of putting a concept to work!

Better Than Naught
Still, we did get to drive, an opportunity not afforded many. And while we wanted more than Audi was able to give, what we got was a good taste for how impressive this car could be with the shackles unbound.

We settled into the R8 TDI's surprisingly spacious and comfortable cabin at 9 a.m. sharp in front of a small audience of cud-chewing beef cattle while the roar of cars practicing for the Sebring endurance race provided background music.

The car doesn't start with a key, but instead with a double poke of the metallic-red start button mounted on the right-hand spoke of the elliptical, racing-style, flat-bottomed steering wheel with its magnesium rim and leather wrapping. The first poke turns on the electronics, the second starts the engine and a third shuts it all down.

Behind the Wheel
The button is surrounded by a rotating "Drive Select" switch that lets the driver choose from three suspension and engine management modes: Dynamic for everyday driving; Sport for a firmer ride and quicker response; and Race for, well, racing (as much as 186 mph in the right circumstances, Audi promises).

Light off the engine in any mode and your ears are treated to the whirr of the starter, a quick rumble as the cylinders fire and then a subdued diesel clatter as the high-pressure diesel injectors pump away, blasting fuel into the cylinders at up to 26,000 psi.

Hit the gas and the tach hits the 5,000-rpm redline in a blink. Even without flooring it, 1st gear in this car with just 60 percent of the torque available feels like compound low in a Mack truck.

No Room to Run
We got enough speed on a couple of runs — 60 mph before Haller, our co-pilot and official minder, apologetically suggested it was time to back off — to move the six-speed manual through the beefy polished-aluminum shift gates all the way to 4th. Had we been able to paste the pedal to the floor, we could have used up all the pavement with just one upshift.

We also discovered that there's enough torque to launch quite pleasantly in 3rd gear, which would come in handy for those who get tired of stirring a manual on crowded freeways (no dual-clutch automated manual for this diesel, as the torque would overpower the transmission gears).

But back to the drive. There wasn't enough of it to provide a solid feel for the car, but we walked away hoping Audi does launch a production R8 diesel. And with the V12, please.

The brief sampling we got showed us a well-mannered but powerful sports car that does Audi, and diesel, proud.

The Le Mans concept is quite a bit heavier than the standard R8, weighing in at almost 2 tons versus 3,439 pounds for the gasser. The V12 diesel and its plumbing add 220 pounds to the R8's weight, while hefty solid-aluminum side-scoop panels and ground-effects trim that probably wouldn't make it to production anyway add 220 pounds more.

Whassa Matter? No Clatter
Turn on the R8 TDI's engine and you know you've got a diesel back there, but it is amazingly civilized given that after squeezing the V12 into the engine bay, there was no room to provide any acoustic insulation. There's minimal diesel clatter, so the R8 V12 TDI sounds more like a family sedan than a brawny, race-bred sports car.

Haller admits to being a little disappointed. Audi engineers tried unsuccessfully to tune the engine and exhaust for a more muscular note — like the rumbling burble that slides from the pipes of the standard V8-powered R8. "Even the racecar is very quiet," he says. "It's just the character" of the state-of-the-art diesel engine.

That engine is a twin-turbo, intercooled, 5,934cc 60-degree V12, no wider than the gasoline-sucking 4.2.-liter V8 in the standard car but 6.5 inches longer and (more important) almost that much taller. A relatively mild compression ratio (for a diesel) of 16.0:1, a sophisticated fuel-injection strategy to reduce knock and low-friction roller cam followers all help reduce noise. Exhaust plumbing includes particulate filters and 6 gallons of urea to knock down diesel particulate emissions so the car meets the strictest U.S., California and European standards.

Shoehorn Situation
It all makes for a tight fit. Haller's team had to reconfigure the R8's aluminum space frame and add a slight bubble to the engine bay's glass cover to accommodate the big diesel. The major issue is the deep oil sump that's required.

Nobody at Audi will admit that the company is planning to do a production model of the car, V8 or V12, but Haller did acknowledge that engineers are still working on development of a dry-sump oil system for the V12 just in case. This would enable the engine to sit lower in the R8's engine bay, improving its fit and lowering the car's center of gravity.

Right now, the engine is topped by a pair of carbon-fiber ducts that bring cold air to the dual turbochargers via the NACA duct on the car's roof, and it sits so high that it obscures most of the view from the rearview mirror. To compensate, Audi added a rear camera that displays on the R8's in-dash navigation and information screen.

Introspection
Other unique interior touches include a metallic-red tachometer dial, loads of carbon-fiber and polished aluminum trim, well-bolstered racing seats wrapped in black leather with red trim, and woven (!) leather floor mats.

The Le Mans Concept features carbon-ceramic brake rotors with six-piston calipers (monobloc in front and fixed calipers in the rear). At the auto shows the car wore custom 20-inch wheels, but for our drive Audi fitted the conventional R8 19-inch wheels with 235/35ZR19 front and 295/30ZR19 rear Pirelli PZero tires.

To let the driver monitor how well the car is dancing in this footwear, the R8 TDI's dash display also graphically illustrates lateral and fore-and-aft G-forces as the car accelerates, brakes and turns.

Bring It On
The numbers never got impressive during our brief flirtation, but the extra weight should help pin all the potential power of the 2008 Audi R8 TDI to the pavement, allowing it to handle as well at its gasoline-burning sibling.

And despite the weight and impressive power numbers, diesel's inherent efficiency gives the car between 22 and 25 mpg, per Audi's internal estimates — something its gasoline-powered rivals cannot boast.

Looks, performance, fuel efficiency and clean emissions — what's the argument for not bringing it to market?