IMSA Prototype Challenge was a racing series featuring two classes of single-seat prototype cars racing simultaneously. The series was sanctioned by the International Motor Sports Association (IMSA). Most races were held in support of the WeatherTech SportsCar Championship. The series raced LMP3 class prototype sportscars. The cars have grown in size and speed since its 2006 introduction, starting from four-cylinder and motorcycle powered race cars to large V8 powered cars. Each race was 1 hour and 45 minutes long apart from the season opening 3 hour race at Daytona International Speedway.