Anti-lag systems are used in some turbocharged cars to improve performance by preventing the turbo slowing down when the driver shuts the throttle to make a gearchange.
On road cars, recirculation systems can be used which take the high pressure created by the turbocharger's compressor and feeds it back to the turbine. This allows the turbo to continue spinning at high speed.
On competition cars a more aggressive form of anti-lag injects fuel into the exhaust system when the throttle is closed during a gearchange to keep the exhaust flow high, even though the engine is not producing much power. The high exhaust flow keeps the turbocharger spinning rapidly, allowing it to quickly rebuild boost pressure when the throttle is re-opened after the gearchange has been made.
