The chuckle came unbidden and unstoppable. Not the polite noise acknowledging the groaner just told by the salesman seated next to you in coach. No, it was the kind of quiet joyous laughter that comes only when all-is-right-with-the-world meets it's-good-to-be-king and 553 lb-ft of torque answer the prod of your right foot. Volkswagen had turned us loose with the new V10 Touareg TDI and I chuckled all day long. If you've read this far you, need a rig with a 7,700-lb towing capability and can afford the $63,000 (with the optional Premium Package), stop reading now and call your dealer. Supplies of the new V10 are severely limited and the US is scheduled to receive only 440 Touareg TDIs this year.

Diesels have long been popular in Europe, not just for heavy trucks but accounting for around 40% of registered passenger cars as well. Recent new car registrations in the EU are running 48% diesel. Saab says the new 9-2X is North-America-only because of the lack of a diesel option. Volkswagen also points to the Great White North, where 40% of the company's Canadian sales--and 70% of Jetta wagons, eh?--are diesels. But diesel passenger car registrations are less than 1% in the United States. Mention diesel and most people here think dirty, smelly, noisy, clattering contraptions. Obviously, "We've got to bust some myths about diesel in America," acknowledges VW's Len Hunt.

In 1990, new emission regulations in Europe forced manufacturers to develop clean(er) diesel technology. Work on injection systems, the combustion process and exhaust gas treatment not only reduced emissions by 90% but found huge gains in torque and horsepower. Sales of diesel powered passenger cars exploded. Now, with rising gas prices and state-of-the-art "Pumpe Duse" unit injector technology coming ashore for the first time, Volkswagen and technology partner Bosch think the same thing will happen here in the States.

Surprisingly, their most important argument for diesel power is performance. According to consumer surveys fuel economy is important but, "It's really the fun-to-drive factor, quick acceleration and pedal response, that sells vehicles in Western Europe," says Bosch's Marcus Parche. The heavy components required to withstand a compression ignition engine's greater internal pressures limit maximum rpm anyway so most diesels are long-stroke designs (good for torque, bad for revs) with up to 50% more torque than a comparably sized gasoline engine. Fuel economy is another plus, roughly 30% greater (diesel fuel not only contains 11% more energy than gasoline but also requires less refining) while CO2 emissions are 20- to 25% lower.

Fifteen years ago Volkswagen decided direct injection using a unit injector (one per cylinder) held the most promise for increased pressures and future applications. Deep in common rail development, Bosch was slow to warm to the idea but VW, who will deliver some 2,000,000 diesels this year, convinced them to join in. The result was "Pumpe Duse," combining the mechanical fuel pump, ECU driven solenoid control elements and direct injection spray holes into a single, compact unit. Built to incredibly precise tolerances (at or under one micro-meter or .00004 in.) the pump can deliver fuel pressures of 2,000 bars (or 29,000 psi and about 20% higher than common rail systems) to the V10's five 0.15 mm injector holes.

The extremely fine spray that results burns more completely, helping power and emissions, and reduces particulate matter formation- something directly related to fuel droplet size. The electronic controls can cycle the injectors up to 10,000 times a minute, completing a full cycle in 1 to 2 milliseconds. The actual injection of 40 or so cubic millimeters (a drop of water) of fuel happens in roughly 10 micro-seconds (1/1000 of a milli-second)! Injection amount, timing and duration are extremely critical for both power and emissions in a diesel engine. A one or two cubic millimeter 'pilot' injection (the size of a pin head) ahead of the main injection starts the burn, reducing emissions and quieting the typical diesel 'clatter'. A similar 'post' injection can also help emissions or be used to 'regenerate' a particulate matter trap.

Oxides of nitrogen (NOx) and particulate matter (soot) are the diesel's biggest emission challenges and new regulations scheduled for 2007 will decrease current standards--already 90% cleaner than 1974--by 95%. With the introduction of the low-sulfur diesel fuel mandated for 2006, conventional catalytic converters could then be used to control NOx and Bosch has developed a particulate filter that will catch 95% of all sizes of soot and last the lifetime of the vehicle. Those gathered to introduce "Pumpe Duse" to the US are confident the new standards can be met.On the road, it is hard to believe you are driving a diesel. Except for a hint at idle, there is little noise outside the cars, we also drove a 2.0-liter Passat TDI, and absolutely none inside to indicate the powerplant's persuasion. There are no glow plug icons to wait for, no clouds of smoke and no funky smell.

2004 Touareg TDI

The new V10 TDI engine was developed with a dual purpose in mind, the steel fist of power for the Touareg wrapped in the velvet glove of highest luxury for the Phaeton. And it's a diesel so it should last forever. VW looked in the parts bin, saw a very nice in-line five there, thought V10 and came up with an exceptionally rigid 90-degree aluminum block with cylinder walls hardened by plasma coating for durability. The 18-degree crank offsets allow uniform firing spacings, a counterotating balance shaft smooths vibrations even more and the vee provides plenty of space for the water pump, water-cooled alternator and intake runners. A helical-cut gear train drives not only the cams but all the accessories--A/C compressor, two oil pumps, coolant pump, power steering pump- as well. No belts to replace. Ever. Cross-flow heads bolt through the block directly to a cast iron bearing tunnel for exceptional overall strength and rigidity.

A single geometry turbo has a single optimal point and leads to charging pressures rising with engine rpms until the wastegate opens, um, wasting energy. VW attacks this problem with ECU controlled step motors that vary the V10's twin turbo's turbine blade geometry based on engine speed, altitude, load and the position of the drive-by-wire throttle pedal. In an effort to keep charge pressure in the optimal zone over a broader rpm range, the turbine blades close down at low engine to use all the available energy in the exhaust gases and gradually open up as rpm and flow increase to both reduce backpressure and keep the compressor from speeding up too quickly. A new six-speed Tiptronic automatic transmission was developed for the V10 with gear ratios designed to better complement its unique power delivery.

All in all, our route through the Virginia countryside showed the Touareg to be a fine driving machine despite weighing nearly three tons. But word is the V6 version is underpowered and the V8 (14 city/18 highway) thirsty. The diesel V10 (17 city/23 highway) and its 553 lb-ft of torque seem a perfect match, especially if you do any heavy-duty towing. Over our 180-mile route, the big diesel never faltered, cruising effortlessly and very quietly at 85 on the interstate, responding instantly while being flogged down the back roads and despite the massive torque, never spinning a tire--unless we asked - while crawling up a wet red-clay fire road. And better yet, despite numerous laughter-inducing attempts to record the lowest possible instantaneous fuel mileage reading--our best was 3.6 mpg--we averaged just over 20 mpg for the route. I don't know if the V10's fuel efficiency is enough to offset the $15,000 premium over the V8 but the driving experience is first-rate. I'd be off to buy a Lotto ticket but until emissions improve, the V10 is a 45-state car not for sale in Maine, Vermont, Massachusetts, New York or California.

2004 Passat TDI

My Mom would love this car, especially the wagon. The most fuel-efficient mid-size car sold in the US, 38 highway/27 city, the 2004 Passat TDI has a range of over 600 miles. That would get her from Watkins Glen past Mid-Ohio and on to Aunt Mary's Cincinnati home nonstop. It might even meet California's LEV II emissions standards when equipped with the particulate filter currently under development in Europe. As my driving partner noted, the drive-by-wire "Pumpe Duse" equipped 2.0-liter diesel four drove like any other Passat you've ever met. In other words, no GTI but a competent, Germanically-solid machine nonetheless. With as much or more room as a Mercedes E-class and wide seats just as comfortable, there's plenty of space for her friends and with 247 lb-ft of torque at just 1900 rpm enough muscle to get them moving. Surprisingly stout at tip-in, with only 134 bhp the Passat still needs a tick over 10 seco. to go from 0 to 60. Mom wouldn't care and I suspect most people shopping Passats won't either. VW has done a great job with NVH, the most intrusive noise--it took us a minute to realize nothing had gone wrong under the hood--was the sudden 100+ decibel buzz of the recently emerged Brood X cicadas as we drove into the Virginia woods.

Of course, the first thing Les asked about was tuning options....

Any TDI wouldn't truly be a Volkswagen without wholly factory unapproved - but not necessarily unappreciated--aftermarket tuning options that are surely on the way. Though no one would speak on the record, one highly placed source said, "Turbocharging lends itself to obvious enhancements and I can imagine some people doing some pretty interesting things". Higher fuel pressures also make more power but just cranking them up to extreme levels is a poor idea for a number of reasons. Like a gas engine, diesels respond best to coordinated efforts to improve airflow and charge cooling, i.e. larger and better flowing intercoolers, turbos and exhausts. (Though VWs aren't mentioned, check out www.bankspower.com for lucid explanations of diesel tuning issues.)

Another engineer-type knowledgeable in such things suggested the first place to start would be engine mapping. There are gains to be found and the fuel injection system will not be the limiting factor. And, it was suggested, perhaps 550 lb-ft of torque is enough, but maybe there are horsepower gains to be found around 4000 rpm. Another coporate insider casually pointed out that racing versions of the five-cylinder the Touareg's V10 is based on put out 300 bhp and the math is pretty simple.

On the downside, these power improvements will probably increase emissions. Optimal injection timing for power is slightly ahead of that most favorable for emissions. The 1.9-liter TDI makes 90 bhp here in the States while the same engine is rated at 150 bhp under slightly less restrictive EU emission regulations. Which brings us to another interesting point. While Bosch engineers worried about the basic structure of the engine and how close it was to the power limits of the design, Volkswagen people expressed a concern for clutches and transmissions (and wondered about brake upgrades). Stronger transmissions both cost and weigh more but there are economies of scale to be considered. A little research might show your 1.9 TDI's transmission well equipped to handle more torque.

Little known facts; to simplify production all, the new New Beetle TDIs automatics are equipped with the DSG transmission. And while small cost considerations and different engine orientations will keep the new 2.0-liter TDI out the current generation Golfs and Jettas their 1.9 liters are all quietly being built with "Pumpe Duse" of their own and now put out 100 bhp and173 lb-ft of torque.

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