The "B" variant of the car, also known as the "fan car", was introduced at the 1978 Swedish Grand Prix as a counter to the dominant ground-effect Lotus 79. The BT46B generated an immense amount of downforce by means of a fan, claimed to be for increased cooling, but which also extracted air from beneath the car. The car only raced once in this configuration in the Formula One World Championship—when Niki Lauda won the 1978 Swedish Grand Prix at Anderstorp.