What the nitrous controller does
Each nitrous stage in NSP is a set of rules. The ECU checks those rules many times a second. When they're all satisfied, it opens the stage's solenoids and applies the fuel and ignition changes you've tuned for it. When any rule stops being true, the stage shuts off. Your job is to decide what those rules are and what the engine needs while nitrous is flowing.
The settings fall into five groups: progressive (how hard the stage sprays), general (when it's allowed to spray), override and enable (driver control), and corrections (what fuel and timing do). The solenoid and switch wiring is covered in nitrous controller wiring. If you're new to nitrous tuning, our article on ECU-controlled nitrous injection is a good primer.
Progressive control
With progressive control off, the stage is simply on or off. Tick Progressive Control and the ECU pulses the solenoid instead, following the N2O Solenoid Duty Cycle table, which appears in the tree once the box is ticked. That lets you bring nitrous in gently so the tires can cope. Frequency sets how fast the solenoids are pulsed. Match it to what your solenoid maker recommends.
Timer mode: what happens after an interruption
Most progressive tables use the Progressive Nitrous Timer as an axis, so duty ramps up as time passes. Timer Mode decides what that timer does if the stage drops out part way through, for example when the driver lifts to catch wheelspin, and then comes back.
| Mode | Timer during the dropout | When the stage comes back | Good for |
|---|---|---|---|
| Resume | Keeps counting | Picks up at whatever duty the table now calls for | Ramps meant to follow race time, not spray time |
| Hold | Freezes | Continues from the duty it had when it cut out | Picking up where you left off after a pedal lift |
| Reset | Goes back to zero | Runs the whole ramp again from the start | Cars that need the soft start every time nitrous re-engages |
Hold and Reset only have any effect when the duty table actually uses the Progressive Nitrous Timer as an axis. If it doesn't, the stage behaves as Resume no matter what you pick. When you're comparing modes, log the timer channel alongside throttle position. You'll see it keep climbing, flatline or drop to zero depending on the mode.
When the stage is allowed to spray
Activation mode
Activation mode is the event that starts the stage once all the safety conditions below are met.
- Race Timer: sprays once the race timer passes the value you set. The Race Timer function must be set up.
- Vehicle Speed: sprays above a set road speed. Needs a working vehicle speed input.
- Always Active: only the general conditions (and the enable switch, if used) apply. This is common on turbo automatics with high-stall converters, where a small shot helps the engine load up against the converter and spool the turbo.
- Trans Brake Release: sprays when the trans brake state goes from active to inactive. Requires Trans Brake Control with at least an input configured.
- Clutch Release: sprays when the clutch switch goes from on to off. Needs the clutch switch function.
- Launch Control: sprays when the launch control output switches off, which is the moment the car leaves. Requires launch control with a launch switch input.
The safety window
These conditions all have to be true before any activation mode can fire the stage. Think of them as a box the engine has to be inside.
| Setting | What it does | Our advice |
|---|---|---|
| Minimum Coolant Temperature | No spray below this coolant temp | Set it to the engine's normal operating temp. Nitrous on a cold engine is asking for trouble |
| Minimum Engine Running Time | Blocks spray for the first few seconds after start | Leave a sensible delay so nothing can fire as the engine catches |
| Minimum / Maximum MAP | Only sprays inside this manifold pressure range | On a turbo car, the maximum stops nitrous stacking on top of full boost if that isn't what you tuned for |
| Minimum / Maximum RPM | Only sprays inside this rpm range | Keep the minimum high enough to avoid big, low-rpm cylinder pressure |
| Minimum TPS | Only sprays above this throttle opening | Essential. Nitrous with a closed throttle has nowhere to go |
| Disable During Limiter | Shuts the stage off while any limiter is cutting, such as the main or launch limiter | We turn this on. Spraying into a cutting engine can cause backfires |
| Main Rev Limit Offset | With the option above on, stops the stage this many rpm before the main limit | Gives the nitrous time to clear before the limiter starts cutting |
Driver control: override and enable
Override lets the driver fire the stage even when the normal conditions say no. It's how you build a purge button, or a push-to-spray button for street use. It needs one or more Nitrous Override functions set up. Leave it on None if you don't need it.
Enable works the other way: it's a master arming switch. Anything other than Always Enabled means the stage can only spray with that switch on. Drag racers typically leave it off in the pits and arm it in the water box or staging lanes. It relies on a Nitrous Enable function.
Corrections while the stage is active
Which bank?
Apply Overall Corrections To Bank should match how the kit is plumbed: both banks, bank 1 only or bank 2 only. The single-bank options suit "banked" nitrous setups. Note that bank-specific timing changes don't show in the main Ignition Angle channel. To see them in NSP or a log, look at the ignition angle for a cylinder on that bank.
Ignition
Ticking Ignition Correction adds the overall ignition correction table. Values are absolute degrees, so a retard is entered as a negative number. Nitrous takes a moment to reach the cylinders after the solenoid opens, and a moment to clear after it closes. Ignition Delay and Ignition Off Delay let the timing change line up with the gas itself, not the solenoid signal. If individual cylinders need different treatment, tick Cylinder Ignition Correction for the per-cylinder tables.
Fuel
Ticking Fuel Correction adds the overall fuel correction table. This one catches people out: unlike most Haltech fuel corrections, it's not a percentage. It's a mass flow of extra fuel. You can show it in g/s, kg/h or lb/h by changing Mass Flow in Preferences > Units Options. Most US tuners work in lb/h. Fuel Delay and Fuel Off Delay do the same job as the ignition delays.
Target AFR
Tick Target AFR Correction to add a table that changes the target air-fuel ratio while the stage is active, so closed-loop fueling aims for a richer mixture instead of fighting the extra fuel.
Bring a new setup up in small steps. Start with a small shot and plenty of timing pulled, confirm fuel pressure and mixture in the logs, and only then add more. Pulling timing costs a little power. Too little fuel or too much timing on nitrous can burn a piston in one pull.
Troubleshooting
| Symptom | Usually |
|---|---|
| Stage never activates | One condition in the safety window isn't met (often coolant temp, minimum rpm or TPS), the enable switch is off, or the activation mode's function isn't configured |
| Nitrous comes back too hard after a lift | Timer mode set to Resume. Try Hold or Reset, and check the timer is an axis on the duty table |
| Can't see the timing change in the log | Bank-specific correction. Log a cylinder's ignition angle on that bank |
| Lean spike right as the stage engages | Fuel Delay too long, or not enough fuel in the correction table |
| Backfire at the limiter | Disable During Limiter off, or the rev limit offset too small |
Nitrous controller FAQ
Why is the nitrous fuel correction in lb/h and not a percentage?
The nitrous adds a fixed amount of oxygen for a given jet and bottle pressure, so it needs a fixed amount of extra fuel. A mass flow correction adds exactly that, no matter what the base fuel table is doing.
Can I run more than one stage?
Yes. Each stage has its own settings and tables, so a second stage can come in later on the race timer or at a higher speed. See our nitrous activation notes, or book a free consultation to plan a multi-stage setup.
