Antilag system

Overview

Anti-lag systems first appeared in Formula One during the 1980s, but fuel restrictions later made them unsuitable there. The technology became common in rally cars due to increased turbo lag from mandated intake restrictor plates, which cause a significant pressure drop and require the turbocharger to spin much faster. An ALS requires an air bypass, either through a throttle air bypass that circumvents the throttle or a bypass that feeds charge air directly to the exhaust manifold.

Types

The throttle bypass or "throttle kick" system combines ignition timing retardation with slight fuel enrichment for cooling. Ignition occurs at 35–45° ATDC, keeping exhaust pressure and temperature high while delivering very little torque to the crankshaft. The higher exhaust pressure, temperature, and mass flow keep the turbo spinning. When the throttle opens, ignition and fuel injection return to normal.

This system stresses the engine, turbocharger, and exhaust manifold due to extreme temperatures and high-pressure pulses; uncontrolled turbo speeds can destroy the turbocharger. This system can be more refined than the throttle bypass type. The street-legal Celica GT-Four WRC homologation model had the plumbing installed but the system disabled. Later Japanese-market Mitsubishi Lancer Evolution models (IV through IX) can have their SAS modified for anti-lag, and the Prodrive P2 prototype uses a modern intake bypass system.