Wow, I love the Porsche Cayenne Diesel review on Edmunds: 2010 Porsche Cayenne Diesel 3.0 TDI First Drive on Inside Line

Farmers and horse owners and truckers already get this, but someday it will be possible to say the word “torque” and not hear crickets chirp in a crowded room of everyday people. Regarding the vast majority of passenger vehicles, torque is the king in how you accelerate, haul, or even lay waste to competitors.

That paragraph is buried down below several other excellent comments.

Here is the meat of the argument for diesel:

…it emits 21 percent less CO2 than the Cayenne’s 3.6-liter gasoline V6 and improves mpg by 39 percent. The Cayenne diesel jumps to 100 km/h (62 mph) from a standstill in just 8.3 seconds, only 0.2 second slower than the gas V6, and this is mainly due to the diesel’s added 154 pounds at the curb (4,939 pounds in total).

You just can’t argue with those numbers. Same performance yet far cleaner output as well as 40% better efficiency! How can this be true? And this is not sold in America because…?

Here is the three-part explanation and analysis for why the engine, although already a match for gasoline performance, is actually in a “tuned-down” configuration:

We asked Klaus-Gerhard Wolpert, Porsche’s man in charge of SUVs, why exactly didn’t Porsche at least goose the output of this engine above its rating of 236 hp and 405 pound-feet of torque just to set it apart from the same engine in the Audi Q7 and VW Toureg. After all, it’s a Porsche.

“You know,” Wolpert said, grinning, “that’s the sort of question my boss [CEO Wendelin Wiedeking] sometimes asks me as well. The challenge is that to add that little burst of power or torque would have first threatened our CO2 rating of 244 grams per kilometer, taking us over the magic 250 level.” (Below 250 grams apparently results in a marked tax and insurance advantage in several countries.)

“Then there’s the sheer cost of the investment to make such changes to existing powertrains,” he adds. “That would have seriously damaged the business case.”

Besides these practical matters, we also got a few Porsche leaders to admit that there could have been certain political risks should Porsche assert its growing powers within the VW Group by demanding the same powertrain as in the VW and Audi but with more of everything.

This is all about risk management. Better efficiency for compliance is nice to see. A better answer would be that they could get more torque without threatening the 250 barrier, but alas they could not and so chose to keep things clean. More standardized parts makes repair and maintenance more likely and less risky, with a lowered cost of ownership. Also nice to see, although it threatens the exclusivity that some might say defines an exotic. The decision to keep it close to a VW and Audi actually probably led to much disappointment among buyers. My bet is Porsche will up the ante this year and next to differentiate, especially after Cargraphic Porsche announced a tuner kit with 215KW(292PS) and 644Nm of torque, giving 0 to 100 km/h in 7.74 seconds (1.27 seconds faster than gasoline). Lumma Design have a similar offering, with exterior modifications to match.

Alas, the Edmunds’ article was written in 2009 and like most at that time it wondered when (not if) this vehicle would arrive in the US. Even the Wall Street Journal has predicted since 2008 that a dozen new high-efficiency diesel vehicles would be introduced to America by now; including the “superclean” Honda four-cylinder 2.2 i-CTDi engine that set world records.

Unfortunately, however, most of the advanced diesel technology is yet to be incorporated into passenger cars here or imported. Auto manufacturers still operate under the mistaken notion that there is no market. Without Dave Hermance, the late Executive Engineer for Environmental Engineering at Toyota, there would never have been a hybrid in today’s market. Who will be the Dave Hermance of diesel?