ADVANCED GUIDE · ANTILAG

Antilag Explained — How It Works, When Workshops Set It Up

Antilag (ALS) keeps turbo boost spooled during throttle-lift on rally / time-attack builds. This guide covers the calibration changes, the hardware stress, and legal status.

What antilag actually is

Antilag (ALS) maintains turbocharger spool during throttle-off events — gear changes, corners, brake zones — by injecting unburnt fuel into the exhaust and igniting it in the turbine housing. The continuous high-pressure pulse keeps the compressor wheel spinning. When the driver gets back on throttle, boost is instantly available with zero lag.

The classic ALS sound (loud crackling backfire on lift) is the unburnt fuel igniting in the exhaust manifold and turbine housing.

The mechanism — overrun fuel + ignition retard

The ECU calibration changes needed for ALS:

• Overrun fuel injection — instead of cutting fuel on throttle-off, the ECU keeps injecting at low quantity.
• Ignition retard — fires the spark very late (or doesn't fire at all), pushing combustion into the exhaust stroke.
• Throttle blip — some ALS systems hold the throttle slightly open during lift to maintain mass flow.
• Wastegate command — wastegate stays closed to force all flow through the turbine.
• Boost target reset — when throttle returns, the boost target instantly snaps to running value.

Softechpro V5 patches these tables on supported platforms — Subaru EJ20/EJ257, Mitsubishi 4G63T/4B11T, BMW S55/S58, Audi RS3 EA888.

Hardware stress

ALS dramatically increases thermal stress:

• EGT spikes to 950-1100°C in turbine housing.
• Cast-iron exhaust manifolds crack within a season. Inconel race manifolds needed.
• Turbine wheels suffer fatigue — race turbos (Garrett GTX-series) survive ALS; stock turbos don't.
• Catalytic converters destroyed in minutes by raw fuel. Most ALS builds run de-cat exhaust.
• Spark plugs foul faster — race plugs and frequent changes mandatory.

Common antilag platforms

ALS is mainstream on rally / time-attack platforms:

• Subaru EJ257 (WRX STI) — classic ALS platform.
• Mitsubishi 4G63T (Lancer Evolution) — Tommi Mäkinen Evo VI Group A standard ALS.
• 4B11T (Evo X) — modern ALS-friendly.
• BMW N54, S55 — ALS via JB4 / Softechpro patches.
• EA888 Gen3 — ALS via custom calibration on Audi RS3 / Cupra Leon Cupra-R.

Legal / homologation

Antilag is unambiguously not road-legal anywhere — emissions, noise and catalyst destruction all fall foul of EU / US regulations. Rally homologation specs (FIA Group N / R5 / Rally2) allow ALS on competition vehicles. Track-day vehicles use it at the operator's risk.

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