Anti-Lag System, ALS, is a system use on mainly turbocharged racing and rally engines to eliminate turbo lag. It was used in the early days of turbocharging in F1 until fuel restrictions made its use unsuitable. Later it became a common feature in rally cars due to the mandated restrictors on the turbocharger inlet. Because of the pressure drop across the restriction, the pressure ratio for a given boost level is much higher and the turbocharger must spin a lot faster to produce the same boost as before. This increases turbo lag significantly compared to unrestricted turbochargers.