Audi R18

New 2011 regulations required a stabilisation fin on the engine cover. The R18 also introduced a six-speed gearbox that was electrically rather than pneumatically controlled, saving weight. The 3.7 L V6 was claimed to develop more than 397 kW (532 bhp), though less than the outgoing R15. It used a single Garrett (Honeywell Turbo Technologies) TR30R VGT turbocharger, unlike the twin TR30R setup of both the Peugeot 908 HDi FAP and the previous Audi R15 TDI. The engine exhausted inwards between the cylinder banks — a "hot valley" configuration — rather than the conventional arrangement where each cylinder bank exhausts outward to separate turbochargers.

The R18 TDI debuted at the 2011 1000 km of Spa round of the Intercontinental Le Mans Cup, finishing 3rd. The car did not enter the 2011 12 Hours of Sebring due to development and logistics reasons, though two evolved chassis were tested. At the 2011 24 Hours of Le Mans, cars #1 (Mike Rockenfeller) and #3 (Allan McNish) were involved in collisions. The #2 of Marcel Fässler, André Lotterer and Benoît Tréluyer won by 13.854 seconds — Audi's eleventh Le Mans win in thirteen years.

For 2012 Audi introduced two variants. Both were reworked to reduce weight, with changes including an Xtrac sequential electrically activated six-speed gearbox housed in a new carbon-fibre composite with titanium inserts, a carbon clutch, modifications to the Dallara-built carbon-fibre composite aluminium honeycomb monocoque, a single Garrett turbocharger with boost pressure limited to 280 kPa absolute, Bosch MS24 engine management, a 45.8 mm air restrictor, OZ magnesium forged wheels, and Michelin Radial 360/710R18 front and 370/710R18 rear tyres.

The R18 e-tron quattro added a 500 kJ flywheel accumulator system designed by Williams Hybrid Power, and two 74 kW Bosch Motor Generator Units driving the front wheels to provide four-wheel drive (quattro). The quattro system was available only above 120 km/h per regulations. Driver Allan McNish described the six automatic driver-selectable modes on the steering wheel as effectively automatic: "I don't have to press a button ... It does it automatically ... It is like traction control."

Both variants debuted at the 2012 6 Hours of Spa-Francorchamps. The #3 R18 ultra of Romain Dumas, Loïc Duval and Marc Gené gave the Ultra a victory over the e-tron Quattro; Audi finished 1–2–3–4. At Le Mans, the e-tron Quattro finished first and second with the Ultra third and fifth, the leading car covering 5,151.8 km with 33 pit stops. At the 2012 12 Hours of Sebring, the #2 of McNish, Tom Kristensen and Rinaldo Capello took overall victory with 325 laps — Audi's tenth Sebring win and Kristensen's sixth.

Audi retired the non-hybrid R18 Ultra for 2013, relying entirely on the e-tron quattro. Car #1 was driven by Lotterer, Tréluyer and Fässler; #2 by Kristensen, McNish and Duval. A third entry (#3) was added — driven by Marc Gené, Oliver Jarvis and Lucas Di Grassi — for use primarily at Le Mans and eligible for manufacturer points only there.

Audi won at Silverstone, Spa-Francorchamps, Le Mans, São Paulo and Austin. At the 2013 Le Mans the #2 car set a qualifying time of 3:22.349 and won the race, with #3 finishing third. At the 6 Hours of Fuji, heavy rain caused the race to be stopped after eight green-flag laps; only the safety-car start laps and early running counted. At the season-closing 6 Hours of Bahrain, the #1 finished second and the #2 retired with mechanical issues. Despite that, Audi won the manufacturers' title by 64.5 points.

For 2014 Audi evolved the car to meet new LMP1 hybrid regulations, switching the chassis constructor from Dallara to YCOM and increasing engine capacity to 4.0 L, producing over 400 kW (540 bhp). A 600 kJ flywheel was retained; both ERS-K (kinetic) and ERS-H (heat) systems were included. New features included blue laser beam backlights with a yellow phosphor crystal lens to complement LED headlights, and a revised V6 TDI with an electric turbocharger and exhaust heat recovery system. Audi later chose not to race with the MGU-H system as it did not produce the expected performance gain and was deemed an unnecessary risk. The aerodynamics were revised: width reduced by 10 cm, height raised by 20 mm, new front wings added, and the exhaust-blown diffuser from the 2013 model was banned and removed.

Porsche returned to prototype racing with the Porsche 919 Hybrid, joining Toyota with the new TS040 Hybrid. At Silverstone, Di Grassi crashed the #1 in the first hour and Tréluyer crashed the #2 late in the race; both cars were finished so badly that new cars had to be completely rebuilt. At Spa the #1 finished second. At Le Mans Audi won, placing them in position to contest the championship. They won at Austin in changeable conditions after making the correct tyre call to wet tyres. At Fuji and Shanghai Audi struggled, and Anthony Davidson and Sébastien Buemi in the #8 Toyota claimed the drivers' title in Bahrain. Toyota also won the manufacturers' title; Tom Kristensen's final race as a driver was at São Paulo, where the #1 finished third.

The 2015 R18 e-tron quattro was upgraded to the 4 MJ hybrid class. The 4.0 L V6 developed 416 kW (558 bhp) and the front axle MGU produced 203 kW (272 bhp), with a flywheel storing up to 700 kJ. The prototype weighed 870 kg. Audi (cars #7 and #8, later joined by #9) won at Silverstone by around four and a half seconds over Porsche #18, and at Spa-Francorchamps by thirteen seconds. At Le Mans the #7 (Lotterer, Tréluyer, Fässler) finished third; a qualifying and race lap record was set by Filipe Albuquerque in the #9 at 3:17.647, later broken by Lotterer's 3:17.476. At the Nürburgring and Austin, Audi finished second through fourth behind Porsche. Porsche won the manufacturers' championship, with the #17 Porsche drivers' title winning over #7 Audi by 166 to 161 in the final Bahrain round.

Unveiled on 29 November 2015, the redesigned 2016 R18 featured a raised nose similar to pre-2014 Formula One designs, air scoops above the front fenders, integrated mirrors, and an AMOLED rearview camera monitor. The KERS changed from a flywheel to a lithium-ion battery in the 6 MJ class. The 4.0 L turbodiesel V6 produced over 390 kW (520 hp) and 850 N⋅m torque; cumulative fuel consumption had fallen 32.4 percent from 2011. The monocoque measured 4,560 mm in length (the regulatory maximum) and the vehicle weighed 875 kg. The e-tron quattro name badge was dropped.

Car #7 was driven by Lotterer, Tréluyer and Fässler; #8 by Oliver Jarvis, Di Grassi and Duval. Audi qualified 1–2 at Silverstone, breaking an eleven-race Porsche pole streak, but the #7 was disqualified post-race for an underbody skid-block infringement and the #8 retired with MGU problems, leaving Audi with only the single pole-position point. At Spa the #8 won after the leading Toyota suffered engine problems. At Le Mans Audi finished third. They won at Spa-Francorchamps and Bahrain and finished second in the Manufacturers' Championship. A post-race disqualification at Silverstone for skid-block non-compliance was not disputed by Audi.

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