Obviously we're not talking about the Q7 itself here. The soccer mom special - particularly in the bizarrely overboard Exclusive concept trim that included enough American Walnut to relay a basketball court - is plainly not deserving of PH Hero status. But the engine beneath the Ipanema Brown paint is a different matter altogether. If the first-gen Q7 was Audi at its most mundane and predictable, the ginormous 6.0-litre V12 TDI was Ingolstadt flexing its technical and financial muscle to a most belligerent, bewildering degree.

Like many of the most interesting engines - although unusually for an oil burner - the unit's genesis was not borne out of any immediate commercial application, but rather the firm's determination to continue a remarkable string of results at Le Mans in the headline LMP1 class (while simultaneously promoting the fuel that was fast becoming Europe's tank-filler of choice). To this end Audi birthed a 5.5-litre V12 motor that developed around 700hp and beyond 800lb ft of torque, all delivered to the back end of the now legendary R10 via a pneumatically-actuated, five-speed sequential gearbox.

Winning the first 24 Hours of Le Mans it entered (and every subsequent one before being replaced by the R15) was a strong statement. Nevertheless, another manufacturer might have baulked at releasing a road-going version of the engine, given its preposterous size and expense - but Audi cheerily rolled out the world's first V12 diesel-engined production car as if it represented the logical end of its sporting investment. In truth, the 6.0-litre unit was not very much like the 5.5-litre race winner - it shared more with the six, eight and ten cylinder oil burners that Ingolstadt was building at the time - although that doesn't mean it wasn't flush with the latest tech; boasting another first with its 2,000 bar Bosch Common Rail injection system.

The V12's provenance hardly mattered in any case, so prodigious was its output and unlikely its installation. Internally, Audi discussed badging the Q7 an RS model; a marketing ploy wisely thwarted by the brain trust at quattro GmbH. The most powerful SUV of its day drives nothing like an RS model: firstly because even back in 2006 it was transparently clear to all concerned that the 5m long SUV had all the dynamic finesse of a bin lorry, and secondly because the V12 hardly helped to alleviate the Q7's weight problem - the Exclusive concept trim driven tipping the scales at 2,635kg.

But the wanton, inapposite charm of the lump is unavoidable. You do not need to open the bonnet or to see the badge to appreciate that there's a reciprocating Goliath lurking under the nose. There's a gentle twist of the Q7 superstructure as it whirrs into life, and while it cannot guffaw or bellow like a petrol-powered V12, it churns with an enormous oily presence. The unit is twinned with a six-speed automatic, one manful enough to live with the job of converting 737lb ft of torque into forward momentum.

Even by today's standards, the scale of that figure is preposterous. A BMW M50d delivers 546lb ft. A Porsche Panamera 4S, 627lb ft. Even the V12's spiritual replacement, the SQ7, with electrically assisted turbochargers, only summons up 664lb ft. Certainly it is faster - by miles - than its forbear, but that's hardly the point. The old Q7 is still a top trump title-holder, and therefore a future object of mechanical lore. It also remains enormously gratifying to drive - in the same way you'd imagine it's probably satisfying to hole punch your bank statement with a jackhammer.

The V12's peak twist is apparently on tap from 1,750rpm, although it doesn't make you wait that long to dispense a keen-edged, rumbling thrust. Driven normally - i.e. briskly, but sanely - the Q7 will barely trouble 2,000rpm, making two and half tonnes feel no more onerous a kerbweight than that of a five-door Fiesta. This was rather the point, of course: that a car of such stupendous proportions could be made to move with the sort of lavish expediency which speaks to the money spent in the engine bay - without necessarily shouting about it.

The V12 does not shout. But with 500hp at 3,750rpm, it does still go. In fact, the manner in which its umpteen moving parts suddenly rouse themselves and have you headlong down the road is affecting, even when put into the context of its quicker, cleverer descendant. The TDI's longer, lustier ratios are certainly easier to mark, and if the slurred upshifts aren't quite as sweet as in the transmissions that followed, well that just makes it an appropriately tangible bit of punctuation between one mighty, fossil-fuel-burning gear and the next. At full stride, the Q7 remains knowingly ridiculous: a long enough straight line will deliver 62mph in about 5.5 seconds, and it sails nonchalantly through the air resistance that normally has a labouring effect on big SUVs at high speeds. Audi says it'll do 155mph - which is entirely believable.

This sinewy amenability, of course, was once the appeal of big-capacity diesel engines to premium carmakers: the quiet, the effortlessness, the understated abundance of power - and, while the 6.0-litre lump will only realistically do about 20mpg - later efforts were fettled for decent economy, too. Now though, with diesel's fall from favour picking up remarkable speed, the writing is on the wall. In the next few decades, no oil burner will do what the V12 does without the assistance of an electric motor in one capacity or another. Given the earth-scorching 298g/km of CO2 emerging from the Q7's exhausts, that's only right and proper. But the V12 is too big, too burly and too outrageous to be airbrushed from history; not least because its like will never come again. Reason enough to usher it respectfully into the PH Hero hall of fame.