Pill has featured some rare cars, but this week's offering can lay better claim to being unique than any of our previous contenders. There are lots of V12 engined cars out there, indeed Pill is slowly working down the list. But there's only one that doesn't require its owner to pay for spark plugs. Yes, it may look like the kind of anonymous middle-aged Q7 in Resale Silver that would blend seamlessly into any UK streetscape, but beneath the bonnet of this week's pick lies a monstrous twelve-cylinder TDI engine. The Q7 6.0 TDI is the only production car to ever have been fitted with a V12 diesel and, given recent trends, we can be fairly confident that record will remain intact.
In the mid-noughties there was something of a diesel arms race going on, although most of this was being fought by Volkswagen Group's different subsidiaries. First came the 5.0-litre V10 TDI, as offered in the Phaeton and Touareg, an engine that quickly earned its own entry in the Encyclopedia of Bork. Then Audi produced a slightly more modest 4.0-litre TDI, which was soon evolved into a 322hp 4.2-litre motor that actually produced more power (but less torque) than the V10 did.
That wasn't enough, though. Diesels needed to get even bigger. After some intense lobbying by manufacturers keen to push their wares into motorsport, it was decided to allow diesel engines to compete under LMP1 endurance racing regulations. Audi had been one of the biggest campaigners for this, being very keen to demonstrate the credentials of its TDI technology. This being, of course, before diesel was discovered to be the planet-choking Fuel Of Beelzebub which we now know it to be.
Hence the R10 race car, with a V12 diesel engine mounted behind the driver. This monstrous unit was heavier than the powerplants of petrol rivals, but also brawnier and with better economy. It worked spectacularly well, the R10 taking three back to back victories in the Le Mans 24 Hours in 2006, 2007 and 2008, plus numerous other race wins around the world.
There was, however, a marketing problem. Beyond some overlapping fuel injection tech, the mid-engined racecar had almost nothing in common with Audi's diesel road cars of the period. Something which frustrated Audi's senior management to the extent that they ordered - as our Prime Minister would probably put it - the spaffing of many more millions to develop a road-going version of the motor.
The original plan for this was an obvious one, to fit it to the R8 and create something vaguely similar to the R10. A concept car built around the engine was shown at the 2008 Detroit Auto Show, and the programme was advanced enough that journalists were promised this was destined to make production; some even got the chance to drive a prototype version. But Audi soon discovered that the costs of reengineering the R8 to accommodate the bulk of the vast engine were too high and the idea was dropped.
Fortunately there was a plan B. Work on putting the engine into a Q7 had been done in parallel and - keen to see something for its huge investment - the board ordered that production of this should go ahead. Having to meet durability and emissions standards meant that the finished road-going engine was substantially different to the one in the racer and much more closely related to the existing V6 and V8 - reportedly the two V12s don't share a single component. But that hardly mattered in the face of numbers that would put many railway locomotives to shame: 493hp at 3,750rpm accompanied by 738lb ft of torque available from just 1,750rpm. Oh, and that torque peak was due to the limitations of the six-speed automatic gearbox; Audi engineers admitted it could have created considerably more twist if left unrestricted.
It was a spectacular piece of engineering. But it was also a deeply flawed car, not least because Audi never seemed to have questioned whether there was demand for such a rarefied beast. In the UK the Q7 V12 TDI listed, indeed nearly capsized, at £96,200, with the possibility to push that into six figures with options. That was nearly twice as much as the already-brisk V8 TDI that sat beneath it in the hierarchy.
In those pre-Bentayga, pre-Urus days that was an unprecedented amount of money for an SUV, twenty grand more than a Cayenne Turbo S. It probably didn't help either that, beyond acceleration which could be likened to a jet aircraft anxious to achieve take off speed on a short runway, the V12 wasn't that great to drive.
It had a predictable amount of hustle, the engine having huge muscle from tickover upwards, and Audi claiming a 5.5-second 0-62mph time and limited155mph top speed. But the rest of the dynamic experience didn't rise above competence at keeping the car's 2.6-tonne mass pointing in the intended direction. It felt every bit as big and heavy as it was, although standard carbon-ceramic brakes - pushed as another crossover from motorsport - meant it never had any difficulty in slowing down. Worse was the V12's lack of aural character - loud and menacing, but never harmonic. As a car it was hugely interesting, but it wasn't very good.
Early buyers also got given what could be described as a residual hosing, the V12 suffering from savage depreciation and a predictably limited secondhand market. There were fans, including some well-known ones. When filling up a then-new 'C7' RS6 at Beaconsfield services I became aware of a very tall man with a Q7 at the next pump who was clearly interested in the RS. We started chatting about it and it took me several seconds to realise that it was Alexander Armstrong, him off t' telly, and that the Q7 was a V12. Something that, to be honest, earned him even more kudos than Pointless Celebrities ever could.
The good news for any potential buyers of our Pill is that the V12 TDI has nothing like the reputation for expensive meltdowns of the lesser V10, although that might well largely be because of just how rare it is. At launch Audi reckoned it would sell around 40 a year in the UK, but that turned out to be woefully optimistic. Across four years of sales just 50 of the V12 found homes here before the car was quietly withdrawn in 2012. That means this car is considerably rarer than the Ferrari 458 Speciale.
While our Pill has obviously been used properly, the 124,000 miles it is wearing don't need to cause excess alarm. Bravery will still be required - the common Q7 parts are all readily available, but any engine problems could turn very spendy very quickly. Few Audi dealers will have seen a V12 Q7, let alone stocked rarer components for them on the shelf.
Yet on the limited evidence of the detail-short advert, this does seem to have been looked after well, with the MOT history being considerably cleaner than the Q7's tailpipe emissions. It is much more expensive than the plentiful V6 and V8 TDI versions, of course - but it's hard to argue against the price given the exclusivity. How often do you get the chance to buy a genuine one-off?
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