What water injection does
Heat is what pushes an engine toward knock. Spray a fine mist of water into the intake, or straight into each cylinder, and it soaks up heat as it evaporates. The charge goes in cooler and the risk of detonation drops. That lets a turbo engine run more boost, or more ignition advance, or a higher compression ratio, with the same safety margin. You'll also hear it called anti-detonant injection (ADI). A few cars had it from the factory, the Saab 99 Turbo S being a well-known example, but today it's mostly an aftermarket addition for performance and racing.
How the Nexus switches it on
The Water Injection function drives an output, usually the pump or a relay for it. It turns on only when three conditions are met together:
| Setting | Condition | Our advice |
|---|---|---|
| RPM | Engine speed must be above this value | Set it where the engine starts making real boost. Once on, it stays on until RPM drops 1000 RPM below this value |
| Load | Engine load must be above this value | Tie it to boost, so cruising at high RPM doesn't spray |
| Air Temperature | Intake air temperature must be above this value | Useful for saving fluid on cool days. Set it low if you want it on every hard pull |
That built-in 1000 RPM hysteresis matters. Without it, the pump would chatter on and off every time RPM crossed the threshold during a shift.
A practical setup
- Wire the pump through a relay to a suitable output. See water injection wiring.
- Set RPM, load and air temperature thresholds on the conservative side, so it comes on early.
- Log the output alongside boost, knock and lambda to confirm it switches when you expect.
- Only then think about adding boost or timing, in small steps, watching knock control closely.
If the map depends on water injection to stay safe, you need a plan for when the tank runs dry or a nozzle blocks. Watch fluid level and flow, and use the engine protection features to pull power back if the system fails. The advanced water injection function adds fuel and ignition corrections for this kind of setup.
FAQ
Does water injection add power by itself?
Not really. It gives you room to add boost or timing safely, and that's where the gains come from.
Why does it stay on after I lift off?
Because of the 1000 RPM hysteresis. It switches off once RPM falls that far below your RPM setting.
Not sure if water injection suits your build? Ask us.
