Activation and recovery
Most rev limits have two parameters - an activation rpm, which is the engine speed when the rev limiter operates, and a recovery rpm, which is where normal engine operation resumes. Normally the recovery rpm should be set 100-300 rpm lower than the activation rpm. A larger different will result in a slower, rougher rev limit.s
Rev limiter type
The ECU uses a fuel cut type of rev limit. The ignition cannot be cut without a fuel cut as this allows the cylinder walls to be washed down by the unburnt fuel. Note that if using a wet type nitrous system with a fuel type rev limit it is important to set the nitrous to be switched off before the rev limiter, otherwise a lean condition will exist when the ECU activates the rev limiter.
Overall limiter
The overall rev limiter is the maximum engine speed the ECU will allow under any conditions. Note than a lower rev limiter may operate when the engine is cold or when the low speed camshaft is in use.
The overall rev limiter will not protect the engine against a 'mis-shift' overrev as the engine is mechanically coupled to the wheels, so rev limiting the engine will not affect the engine speed.
Overrev rpm
The overrev rpm is the engine speed where the ECU will generate a fault condition. This should be set about 200 rpm higher than the overall rev limiter.
Launch limiter
The launch limiter is active when the vehicle is not moving for drive-train protection. The launch limiter acts the fastest when the cut and recover rpm are the same.
Speed limiter
The speed limiter activates at the indicated speed. To disable the speed limiter enter a value larger than the top speed of the vehicle.
Boost Cut
The boost cut will rev limit the engine if the manifold pressure rises above the specified pressure. This helps to protect the engine from over-boost. The boost cut is only active over 2000 rpm, to ensure the engine can always be started.
Boost Cut with a stock MAP sensor
Care must be taken when setting a boost cut near the limit of a MAP sensor. The stock MAP sensor can read to around 1.78 bar (approx 11.5 lbs boost pressure), but to ensure the MAP sensor will generate a voltage high enough to trigger a boost cut it is not recommended to set the boost cut over 1.75 bar (11 lbs) with a stock MAP sensor.