Formula One, abbreviated to F1 and also known as Grand Prix racing, is the highest class of single-seat open-wheel formula auto racing. It consists of a series of races, known as Grands Prix, held on purpose-built circuits or closed city streets, whose results determine two annual World Championships, one for drivers and one for constructors. The cars race at speeds often in excess of 320 km/h (200 mph). For 2006 a new formula has been implemented in order to slow the cars down. It consists of normally-aspirated V8 engines with a displacement of 2.4 litres, providing around 750 bhp at nearly 20,000 rpm. Furthermore a special emphasis is put on electronics, aerodynamics, suspension and tyres. However, the formula has seen many evolutions and changes through the history of the sport. The powerplants used have ranged from normally-aspirated straight-4 engines to supercharged V12 engines, the levels of displacement have ranged from 1.5 litres to 4.5 litres, and the maximum power achieved in the history of the series has been around 1200 bhp, during the turbo era.