What the Aux Limiter is for
Your main RPM limiter protects the engine all the time. The Aux (auxiliary) RPM Limiter is a second, temporary limit that's only active when you switch it on through an input. Common uses:
- Valet mode: cap revs when someone else is driving.
- Basic launch control: hold RPM on the line with a clutch or button switch.
- Pit or burnout limit: a lower ceiling for specific situations.
It needs an input to activate. See Aux Limiter wiring for how to assign it, and RPM Limit for setting the limit itself. For a full launch strategy with boost building, launch control is the better tool.
Cut type: how hard the limit hits
| Cut Type | How it limits | What it feels like |
|---|---|---|
| Hard Cut | Cuts every cylinder at the limit, then restores them once RPM drops by the hysteresis amount | Abrupt, bouncing on the limiter |
| Soft Cut | Randomly drops individual fuel or spark events, calculated firing event by firing event, to hold RPM at or under the end RPM | Faster to respond and much smoother |
| Cut Off | Applies a percentage cut you define, with a cut pattern you choose | Anywhere from smooth to aggressive, and you can change the sound |
For valet use we like Soft Cut, since it's gentle and the driver barely notices. For launch, Cut Off gives you control over how the limiter sounds and behaves; cut percentage covers those settings.
Cut method: fuel, spark or both
- Ignition: drops spark events. This is the method most people use, and the one we start with.
- Fuel: drops injection events. Some engines are fussier about fuel returning after a cut, so we test it before relying on it.
- Fuel & Ignition: drops both together.
An ignition cut leaves unburned fuel in the cylinder that can light off in the exhaust. That's the source of the popping launch limiter sound, and it adds heat to the exhaust and turbo. Keep time on the limiter short.
Cut hysteresis
Hysteresis only applies to Hard Cut. It's how far RPM has to fall below the limit before the ECU brings fuel or spark back. A small value gives a fast, buzzy limiter; a larger one gives slower, heavier bouncing.
Related settings
The Adder article covers the remaining option in this function. If you're on an Elite, see the Elite auxiliary RPM limiter instead.
