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The 3.0L V6 in the 2009 Touareg TDI consists of the same diesel engine and emissions after treatment system as in the Audi Q7 TDI. They differ in injection strategy. The automatic transmission in the sportier Q7 is programmed to hold lower gears (from 0-60 mph) slightly longer that the Touareg, and as a result the Bosch piezo injectors spray 5% more diesel in the chamber each time it shifts up a gear to avoid lag.

Touareg TDI, Then and Now

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Frugality was hardly in style when Volkswagen Touareg TDI joined the fraternity of V10 trucks stomping around America in 2006. The 310-hp twin-turbo 5.0-liter diesel, which produces a massive 553 lb-ft of torque @ 2,000 rpm, could move the Touareg’s substantial girth of 5,825 lb from 0 to 60 mph in 7.5 seconds, tow 7,716 lb, and delivered 17 mpg city/22 mpg highway. (There was a 2.5 liter TDI Touareg, but that version stayed home in Europe).

Since then, VW has been embracing engine downsizing in a major way, such as developing a 3.0-liter V6 diesel that’s now available in the Touareg. It produces 225 hp and 407 lb-ft of torque, so it is still capable of towing 7,716 lb as the V10. While it is a bit slower (0 to 60 mph in 8.7 seconds rather than 7.7 seconds—although who is drag racing substantial SUVs?), it turns in better highway fuel efficiency—17 mpg city/25 mpg highway—and is 520 lb. lighter at the curb than its predecessor.

The V6 TDI is the first diesel in a new generation of V-engines from VW with a 90° bank angle. There is a 90-mm distance between the cylinders. The cylinder housing is vermicular graphite cast iron, which VW notes is 15% lighter than conventional cast iron. Along with its chain drive, the design principle makes for a very compact 17.3-in. long engine. A Honeywell/Garrett turbocharger provides boost.

The V10 may have been the first off-road, turbo-diesel, light-duty vehicle in the U.S. market with a particulate filter, but it still left its CO2 mark with 469 grams/mile; while the V6, coupled with an AdBlue (urea) after treatment system, puts out 420 grams/mile in combined city and highway driving.