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.