What this node controls
The anti-lag Wiring node decides when anti-lag is allowed to work. It doesn't set how much fuel or timing is used. That lives in the enrichment, ignition and idle valve bypass tables, all part of the main anti-lag function. Here, you pick the arming method and, if a switch is involved, tell the ECU how to read it.
Choosing an arming method
| Arming Method | Anti-lag arms when | Good for |
|---|---|---|
| Engine Demand | The engine demand conditions are met. No switch involved | Dedicated race cars where anti-lag should always be ready |
| Switch Only | The enable switch is on | Letting the driver decide, with arming kept separate from throttle |
| Engine Demand & Switch | Both the demand conditions and the switch are satisfied | Most cars that also see the street, pit lane or trailer |
Our preference for almost every customer car is Engine Demand & Switch. Anti-lag stays completely off unless the driver has flipped the switch, and even then it only acts when the engine conditions say it should. That protects the turbo and exhaust from anti-lag running in traffic, in the pits, or while someone else is driving the car.
Wiring the enable switch
If your arming method uses a switch, assign it an input under Connections. Either an SPI or an AVI will work. A panel switch such as the Haltech dual switch panel kit is a tidy way to add one.
Using an SPI
| Setting | What it does | Our advice |
|---|---|---|
| Edge Select | Tells the ECU which transition means "on" | Falling if the switch connects the input to ground. Rising if the switch feeds the input a voltage |
| Sensor Type | How the SPI treats the signal | Hall Effect for any switch input |
| Pullup | Holds the input at a voltage while the switch is open | On for a switch that only grounds the input, otherwise the input floats when off |
The most common and robust setup is a ground-switching toggle: one side of the switch to chassis or signal ground, the other to the SPI, pull-up on, edge set to Falling.
Using an AVI
An analog input doesn't have an edge. Instead you give it two voltage thresholds:
- Switch On Voltage: once the input crosses this level, the switch counts as on.
- Switch Off Voltage: once the input crosses back past this level, the switch counts as off.
Each threshold can sit above or below the other, depending on whether your switch pulls the input up or down. Keep a healthy gap between them. That gap stops a noisy or sagging signal from flicking anti-lag on and off, and leaves room for normal voltage fluctuation.
Worked examples
Switch that grounds the input
Say the input rests at about 5 V with the switch off, thanks to the pull-up, and drops to near 0 V when the switch closes to ground. A sensible setup is an On Voltage of 1.0 V and an Off Voltage of 4.0 V. The ECU sees "on" once the input falls under 1.0 V and "off" only after it climbs back over 4.0 V. Anything in between leaves the state unchanged.
Switch that feeds the input
Now flip it around: the input sits near 0 V when off, and the switch connects it to the ECU's 5V supply when on. Set the On Voltage to around 4.0 V and the Off Voltage to around 1.0 V. The input has to rise above 4.0 V to arm and fall below 1.0 V to disarm.
In both cases, check the real voltages in the NSP channel display with the switch in each position before you settle on thresholds. Wiring, pull-ups and switch lamps can all shift the numbers a little.
Anti-lag puts a lot of heat and pressure into the exhaust side of the turbo. Make sure it can't be left armed by accident, and log EGTs and turbo speed when you're tuning it. If you're unsure it's right for your setup, book a free 30-minute consultation with us first.
Troubleshooting
| Symptom | Usually |
|---|---|
| Switch state never changes in NSP | Wrong input assigned, or a ground-switching switch with the pull-up turned off |
| Switch state is backward | Edge Select reversed on an SPI, or On and Off voltages swapped on an AVI |
| Anti-lag flickers on and off | AVI thresholds too close together, or a poor switch ground |
| Switch reads on, but anti-lag never activates | Arming set to Engine Demand & Switch, and the demand conditions aren't being met |
FAQ
With Switch Only, do the other anti-lag settings still matter?
Yes. The arming method only decides whether anti-lag is allowed to run. How hard it works, through fuel, timing and bypass air, still comes from the anti-lag tables, so those need tuning either way.
Which is better, SPI or AVI?
Both work. We tend to keep SPIs for speed and position signals and put switches on AVIs when inputs get tight, but either is fine for a simple on/off switch.
