The Audi R10 TDI (Turbo Direct Injection) is a sports prototype designed and built by Audi in partnership with Dallara. Built to the Le Mans Prototype 1 (LMP1) regulations, the R10 was highly successful throughout its career; the R10 became the first diesel-powered car to win the 24 Hours of Le Mans in 2006, in what would be the first of three 24 Hours of Le Mans wins. Unveiled to the public on 13 December 2005 in Paris, the R10 would go on to win the 2006 24 Hours of Le Mans just 200 days later.
The R10 was eventually replaced by the R15 TDI at the conclusion of the 2008 American Le Mans Series. Colin Kolles of ByKolles Racing (known then as 'Kolles') fielded the car for two more years at Le Mans and for a single year in the 2009 Le Mans Series.
Background The R10's predecessor, the R8 Le Mans Prototype, was an open-cockpit design based on experience gained with the Audi R8R. The R8R's sibling, the closed-cockpit R8C, was not as successful as the R8R and Audi chose open-cockpits as their design philosophy, this remained the case until 2011, when the R18 TDI was unveiled with a closed-cockpit. A key difference between open- and closed-cockpit designs such as the Bentley Speed 8 was that the closed-cockpit prototypes of the LMGTP class ran with narrower tyres, but had larger air restrictors and thus produced more power compared to its fellow open-cockpit LMP1 cars.
The R8 proved to be one of the most successful sports prototypes of all time, dominating the LMP900 class from its introduction in 2000, scoring 63 victories from 79 races. Eventually, weight and air restrictor penalties resulted in the R8's competitors becoming increasingly closer on pace, for the 2005 edition of the 24 Hours of Le Mans the R8 was forced to carry extra in ballast and had smaller air restrictors. These changes to the regulations meant that the V8 in the R8 LMP was becoming obsolete. The 2005 Le Mans Endurance Series finale at Istanbul saw the end to the R8's racing activities in Europe, however, akin to what was done with the R8R, the R8 replaced the R10 following the latter's debut at the 2006 12 Hours of Sebring until the 2006 24 Hours of Le Mans.
The R8 LMP was renowned for its serviceability, especially the rear assembly, which was nicknamed "Hinterwagen". The serviceability trend continued with the R10, with not only the rear bodywork being removable but the front crash structure too. The R10 carried over the R8's carbon fibre monocoque and aluminium honeycomb, with the plastic bodywork replaced by a carbon-fibre composite construction, necessitated by the increased weight of the V12 compared to the previous V8.
Engine and transmission
Audi was not the first to campaign a diesel-powered car at the 24 Hours of Le Mans, with French brothers Jean and Jacques Delettrez being the first to field a diesel. They entered the 1949 24 Hours of Le Mans with a car that had bodywork by Delage and was powered by a inline-6 producing . They retired after completing , having run the starter motor battery dry after attempting to travel back to the pits after the car had run out of diesel.
After retiring with valve failure in 1951, the Delettrez brothers were the last diesel-powered entrant until privateers Taurus Sports Racing entered the 2004 24 Hours of Le Mans with a Lola B2K/10 that was powered by a V10 TDI from a Volkswagen Touareg. The first success of a diesel-powered race car was a BMW 320d that won the 1998 24 Hours of Nürburgring.
In January 2002, head of Engine Technology at Audi Sport Ulrich Baretsky sat down over a beer with Automobile Club de l'Ouest officials Daniel Poissoneaux and Daniel Perdrix in Ingolstadt to discuss the direction racing would take in the future. During that conversation Baretsky realised that 50% of European cars on the market were powered by diesel engines, prompting Baretsky to suggest to head of Engine Development at Audi Wolfgang Hatz the idea of a diesel-powered race car. Hatz supported the idea, citing how the technologies pioneered in a diesel-powered race car could be carried over into a road car, or vice versa, such as FSI technology which was being used in the R8 LMP's and Audi's road car engines. Wolfgang Ullrich, head of Audi Motorsport, also saw the potential in a diesel-powered race car, as the American Le Mans Series was part of Audi's competition calendar, and Audi was looking to introduce its diesel road car range to the United States. Ullrich wanted to change the stereotype of diesels being dirty and "oil-burners", and that he "wanted to push the sportiness of the diesel", and "the best way to do that was through motor sport [sic]." Then-chairman of the board of Audi AG Martin Winterkorn reiterated this during the car's presentation in Paris in 2005, saying "The Le Mans project will help our technicians to extract even more from TDI technology".
During the 2004 24 Hours of Le Mans, Baretsky met with the then-chairman of the supervisory board of Volkswagen, Ferdinand Piëch, who gave the project the go-ahead. The first engine prototype was a production-based Audi V8 with a similar bore and stroke to the V12 intended for use in the race car, and its first runs on the dyno came in early 2005. By the time of the R10's unveiling in December of that year, the engine was said to have completed around 1,000 hours on the dyno. The engine presented several unique challenges for Audi, one of which was the construction of the engine block. Wolfgang Appel, director of Vehicle Technology at Audi, compared the task to the Apollo program, saying "In the beginning they [the Americans] did not know what was going on, nor did we!" At the time, all of Audi's road car diesel engines used vermicular cast iron, and head of Audi Diesel Engine Development Richard Bauder suggested that like the road cars, the race car block should be machined from cast iron. Baretsky rejected the idea on the grounds that a cast iron block was too heavy, opting for an aluminium-silicon alloy block instead. The Bosch Motronic MS14 engine control unit (ECU) was also bespoke, with Bosch having never written software for an engine this powerful. A Bosch common rail fuel injection system with piezoelectric injectors delivered fuel into the cylinders at over , combined with a Garrett turbocharger for each bank (limited to ), resulted in a power output of over between 3,000 and 5,000 rpm and a torque output of .
Dow Automotive also developed and manufactured a specialised diesel particulate filter (DPF) for the R10. The particulate filter consisted of a chemically treated ceramic honeycomb structure, which had a distinct microstructure that reduced weight and had a high porosity. The filters were so efficient that exhausts from the engine were practically transparent, and the exhaust note was around 5 dB quieter than the R8, at 105 dB. Allan McNish said the exhaust was so quiet that above , the sound of wind rushing by was louder than the engine itself, making downshifting hard to do by ear. A complication with the diesel particulate filters arose when deciding where to mount them; Audi eventually settling on mounting them aftwards at the end of the exhaust pipes. This somewhat disturbed the R10's weight distribution, with Baretsky commenting that "We'd be happier to have them [the filters] closer to the engine, but this would have put them in the middle of the rear axle". After the 2006 race, Baretsky was said to have wiped the inside of the No. 8's exhaust pipes whilst the car was in parc fermé, and Ralf Jüttner, team director of Joest Racing, remarked that afterwards "the napkins were as pristine-white as before".
The immense power produced by the engine also required a new gearbox. A favourable torque curve meant that a 6-speed like the one found in the R8 was unnecessary, and Xtrac provided a 5-speed pneumatically-actuated sequential with a ZF Sachs ceramic clutch, and Megaline supplied the gearbox control system. Despite the vastly superior torque, the new gearbox is lighter than the R8's gearbox. It is a thin walled aluminium casting, as opposed to its predecessor's Ricardo magnesium case. Bosch also supplied the car with its Acceleration Slip Regulation unit.
Along with the engine's high power and torque figures, its efficiency was among the highest in racing engines of its era. The car's fuel at the 2006 and 2008 24 Hours of Le Mans was , and , respectively (the latter race being hampered by rain). In comparison, a 2007 Formula One car was said to have a fuel efficiency of around . This efficiency meant that the R10 was able to run longer stints than the R8, and proved to be integral to Audi's success at the Circuit de la Sarthe. Victory at the 2006 race saw Audi run 4 more laps per stint than its closest competitor, the petrol-powered Pescarolo-Judd, and victory at the 2008 24 Hours of Le Mans came courtesy of the diesel Peugeot 908 HDi FAP needing to pit a lap earlier than the R10 to take on fuel, despite being a quicker car.
Racing history 2006
The R10's debut season saw Joest Racing handling the R10's Le Mans duties, and partner with Champion Racing at Sebring. Champion Racing continued to field the car in the American Le Mans Series, although the R10 was replaced by the R8 following Sebring and was not reintroduced until the fifth round of the season at the 2006 Utah Grand Prix. Sebring acted as a testing ground for Joest Racing as preparations in Europe began for that year's 24 Hours of Le Mans in June. Ullrich said the rationale behind fielding the older R8 was that the R10 project required more development, saying "We used Sebring as a testing ground, but until Le Mans was done we used the existing R8 in the US".
Le Mans
Joest Racing's Le Mans campaign did not start off smoothly, with an issue with the piezo-electric injectors surfacing. The injectors behaved unusually during qualifying and the race, because of the constant development and modifications to the engine throughout 2006, Audi would be in constant communication with Bosch to try and resolve the problem. A temporary measure implemented was to limit the distance covered by each engines through qualifying, so as to preserve them for the race. Despite this, Rinaldo Capello put the No. 7 R10 on pole with a time of 3:30.466, alongside him was the sister No. 8, with Marco Werner setting a time of 3:30.584, over 2 seconds faster than the nearest petrol-hybrid Pescarolo-Judd C60s, which lined up in the second row.
The injector problem resurfaced during the race, with the No. 7 car coming into the pits in the fourth hour to replace an injector that had failed. The faulty injector held the car up for twenty minutes, because the software could not pinpoint exactly which injector had failed, only which bank it was in. Audi eventually replaced the entire right-hand bank of injectors, and the No. 7 rejoined in 14th place, six laps behind the leading No. 8. Repairs to fix contact with lapped traffic and turbo failure cost the No. 7 almost an hour in the pits, effectively ruling it out for the overall win.
The No. 8 was not affected by injector issues, with its only unscheduled appearance in the pit lane coming early in the morning of the following day for a gear cluster change. The No. 8 went on to take the overall win in a record 380 laps @ , 4 laps ahead of the No. 17 Pescarolo-Judd, and the No. 7 sister Audi rounded out the podium, finishing 13 laps behind the leader. Kristensen also set the record for longest stint at the time in an LMP1 car, covering 16 laps in a single tank of diesel, along with setting the fastest lap, clocking a 3:31.211 en route to his podium finish. The R10's victory was the first triumph of a diesel-powered race car in a major event since a Cummins Special qualified on pole for the 1953 Indianapolis 500, and the first diesel race car to win the 24 Hours of Le Mans. Pirro also extended his consecutive podium finishes to eight.