What anti-lag actually does
Lift off the throttle on a turbo engine and airflow collapses. With no exhaust energy to drive it, the turbine slows down, and when you get back on the throttle you wait for it to spool again. Anti-lag keeps air flowing through the engine while the throttle is shut, then retards the ignition so hard that the mixture makes very little torque and a lot of hot, high-pressure exhaust. The engine doesn't rev, but the turbine stays fast. It's most useful across gear changes and between corners.
It is hard on parts. Exhaust valves, manifolds and turbos all take a beating, which is why the Elite anti-lag function has so many limits built in. Use them.
Step one: getting extra air in
The amount of boost anti-lag can hold depends mostly on how much extra air you can feed the engine with the throttle closed. There are two ways to do it on a cable throttle:
- Through the idle system: the idle valve opens to let air bypass the throttle. That's controlled by the Idle Valve Bypass table below. It's simple, but an idle valve only flows so much.
- Through the throttle body: open the throttle stop until it passes the air you want, then recalibrate the TPS so that new resting position reads 0%. Idle would now be far too high, so enable and set up Rotational Idle to cut cylinders and bring idle speed back down.
With drive-by-wire you don't need either trick. The ECU can simply open the throttle itself during anti-lag, so there's no need to touch the throttle stop or use rotational idle.
Wiring tab: how anti-lag gets armed
Arming method
| Arming Method | What arms it | When we use it |
|---|---|---|
| Engine Demand | Throttle or pedal position only | Dedicated race cars where anti-lag is always wanted |
| Switch Only | A driver switch only | Rarely on its own. The engine demand checks are valuable |
| Engine Demand & Switch | Both have to agree | Our usual choice, so the driver can turn anti-lag off in the pits or on the road |
Setting up the enable switch
If a switch is involved, pick an input for the Anti-Lag Enable Switch. It can be an SPI or an AVI, and each needs slightly different setup.
On an SPI:
- Edge Select: Falling if the switch grounds the input when it's on, Rising if the switch feeds voltage to the input when it's on.
- Sensor Type: Hall Effect for any switch.
- Pullup: turn it on when the input needs something to pull it up to a voltage while the switch is open, which is the case for a switch to ground.
On an AVI, you tell the ECU what voltage counts as on and what counts as off with Switch On Voltage and Switch Off Voltage. The trick is to leave a gap between them. The ECU only changes state once the voltage crosses the far threshold, so electrical noise near the middle can't flick anti-lag on and off.
Take a switch that sits at 0V when open and gets 5V when closed. Set the On voltage near the top (say 4.0V) and the Off voltage near the bottom (say 1.0V). The switch reads on once it rises past 4.0V, and doesn't read off again until it drops below 1.0V. If your switch works the other way round, pulled high when off and grounded when on, the On threshold goes near the bottom and the Off threshold near the top. Check what the input actually reads in ESP with the switch in each position before choosing values.
Anti-lag tab: the conditions
Anti-lag works in two steps. First the driver has to go past the arming throttle (or pedal) to build airflow. Then anti-lag activates when they lift below the activating threshold. Engine demand means TPS on a cable throttle and APP on drive-by-wire.
| Setting | What it does | Default | Our advice |
|---|---|---|---|
| Arming Engine Demand | Demand the driver must go past to arm anti-lag | 50 | High enough that anti-lag only arms after real throttle, not light cruising |
| Activating Engine Demand | Demand the driver must drop below for anti-lag to kick in | 1.0 | Close to fully off, so a partial lift in a corner doesn't trigger it |
| Min RPM | Anti-lag stops below this engine speed | 3000 | Keep it out of the rpm range where you'd be pulling up at a stop |
| Max Time | Longest anti-lag can run before it must be re-armed | 5.00 | Keep it short. Long anti-lag events cook turbos and exhausts |
| Max Coolant Temp | No anti-lag above this coolant temp | 110 °C (230 °F) | Protects an engine that's already hot |
| Min Coolant Temp | No anti-lag below this coolant temp | 60 °C (140 °F) | Stops heavy wear from anti-lag on a cold engine |
| Max EGT | No anti-lag above this exhaust temperature (only shown once an EGT sensor is set up) | 1000 °C (1832 °F) | If you run anti-lag seriously, fit an EGT sensor and use this |
The three anti-lag tables
These tables only apply while anti-lag is active. The enrichment and idle valve bypass tables are often mapped against Anti-Lag Trigger Time Remaining. That lets you use the strongest settings at the start of an event, when you most need boost, and ease off as it runs out.
Enrichment
Extra fuel during anti-lag helps build exhaust energy to keep the turbine spinning. The typical shape is the most fuel at the start of an event, tapering to no correction as time remaining reaches zero.
Ignition advance/retard
This is the heart of anti-lag. A large amount of retard means the engine keeps flowing air but makes almost no crankshaft torque, so it doesn't rev up. The burning mixture ends up in the exhaust, where it keeps pressure on the turbine.
Idle valve bypass
If you're getting extra air through the idle valve, this table sets how far it opens during anti-lag. It's usually wide open (100%) early in the event and tapering to 0% at the end.
Anti-lag trades parts life for response. Expect faster wear on turbos, exhaust valves and manifolds. It's rarely worth running on a street car, and never without the temperature and time limits configured.
Troubleshooting
| Symptom | Usually |
|---|---|
| Anti-lag never activates | Arming demand never reached, activating threshold too low for your TPS calibration, rpm below Min RPM, coolant outside the window, or the switch not seen |
| Engine revs up during anti-lag | Not enough retard, or too much extra air for the timing you have |
| Very little boost held | Not enough extra air. Check the throttle stop setting or idle valve bypass values |
| Idle is too high after opening the throttle stop | Rotational idle not enabled or not tuned, or TPS not recalibrated |
| Switch flickers on and off | AVI on/off thresholds too close together, or the wrong edge or pullup on an SPI |
Running a Nexus ECU? See the Nexus anti-lag article. For roll-race style launches, see rolling anti-lag. Anti-lag also works closely with boost control.
Anti-lag FAQ
Does anti-lag work with a cable throttle?
Yes. You provide the extra air with the idle valve or by opening the throttle stop, then use rotational idle to keep idle speed normal. Drive-by-wire is simpler because the ECU controls the throttle directly.
Is anti-lag the same as launch control?
No. Launch control holds rpm on the start line to build boost before the car moves. Anti-lag keeps the turbo spinning when you're off the throttle while driving. Many race cars use both.
