Audi/Bentley 90° twin-turbocharged V8 racing engine
The Audi/Bentley 90° twin-turbocharged V8 racing engine is a 3.6-liter and 4.0-liter, twin-turbocharged, four-stroke, 90-degree, V8 racing engine, used in the Audi R8C, Audi R8R, Audi R8 and Bentley Speed 8 Le Mans Prototype race cars, between 1999 and 2005. Audi R8C/R8R engine
The R8C and R8R both use 3.6-liter, twin-turbocharged V8 engines, producing between , and between  of torque, while using two  air restrictors, and pushing  of absolute boost pressure. While the R8R has a large number of vents placed on the nose, most of the intakes and air exits on the R8C are placed on the sides. The R8R was estimated to boast around  from its V8 engine, allowing it to hit  in 1999 at Le Mans (the original claims were that the car could go ). Audi R8 engine
The R8 is powered by a 3.6 L Audi V8 with Fuel Stratified Injection (FSI), which is a variation on the concept of gasoline direct injection developed by VW; it maximizes both power and fuel economy at the same time. FSI technology can be found in products available to the public, across all brands in the Volkswagen Group. The power supplied by the R8, officially listed at about  in 2000, 2001, and 2002,  in 2003 and 2004, and  in 2005, is sent to the rear wheels via a Ricardo six-speed sequential transmission with an electropneumatic paddle shift. Unofficially, the works team Audi R8 for Le Mans (2000, 2001, and 2002) is said to have had around  instead of the quoted 610 hp. The numbers were quoted at speed, and were due to the car making 50 extra horsepower due to twin ram-air intakes at speeds over . Official torque numbers were quoted for this version of the engine at  at 6500 rpm (2004/2005), but the 2002/2003-spec engine produced more torque; with  at 5500 rpm, with boost pressure set at  absolute. The equation for horsepower (torque divided by 5250, multiplied by rpm) for these numbers produces a horsepower rating of  at the same 6500 rpm (516/5250*6500=638). Restrictor changes for 2003 brought the power down to 550 bhp for anyone still racing with the R8, but the maximum torque hardly changed. For 2005, The ACO still felt that the R8 needed to be kept in check, so they reduced the restrictor size on the R8's engine, due to the car not meeting new hybrid regulations, and stipulated the car shall carry ballast weight in an attempt to make the races more competitive. The R8 was restricted even further to only 520 bhp. Bentley Speed 8/EXP Speed 8 engine
The engine from the Audi R8, a 3.6-liter V8, with (Honeywell Turbo Technologies) turbocharger, was used as the initial powerplant for the Bentley in 2001. It produced  and over  of torque, via two  intake restrictor, with boost pressure limited to  by regulations. Following its initial year of competition, the Audi-sourced V8 was modified to better suit the EXP Speed 8. This saw the engine expand to 4.0 liters, producing between , and  of torque, using two  intake restrictor plates, with boost pressure still being limited to  by regulations. This would ultimately lead to Bentley redesigning the car for 2003, leading to the change of name to simply Speed. Without the intake restrictor plates (completely unrestricted), and with boost pressure set at around , the 4.0-liter engine is reportedly capable of producing up to , and about  of torque. Applications
Audi R8C
Audi R8R
Audi R8
Bentley Speed 8

References

Volkswagen Group
V8 engines
Audi engines
Bentley engines
Volkswagen Group engines
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Internal combustion engine