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HOWTO: Remove speed limit

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On drag cars or on the dyno depending on your gearing and rpm limit, you may find a speed limit is occurring.

There are two methods to disable the speed limit.

Method 1 (maximum speed of 255 kph)

For standard gearing and the 6 cylinder, this is usually sufficient. For the V8s spinning to 7-7.5k, you may need method 2.

This method assumes the VID block is enabled (it is by default).

auF0389 Activate/Deactivate VID Block Parameters for Final Drive/Tire etc = Enabled

If the VID block is enabled the following scalar is used to determine the speed limit.

Speed_limit_kph

This scalar is limited to a maximum of 255 kph as the underlying datatype is a byte. If you need more than 255kph (can appear as low as 240kph on a roller dyno).

Method 2 (unlimited speed limit).

To use method 2 you must first disable the VID block by setting auF0389 to Disabled. Note that Mk2 Falcons use these overrides regardless of the setting above.

IMPORTANT NOTE If you disable the VID block, this means the PCM will now use the values found in "VID Block Calibration Overrides" such as axle/diff ratio and various other scalars. Ensure the following parameters match their corresponding values in the VID block. Note that some of the scalars in the VID block may be set out of range, if they are set out of range you can simply leave them.image.png.4478e511de12d3ccae56743126c2068e.png

Now you can use auF0397 Speed Limit No VID to set the limit. This is a floating point and can be safely set out of range to 1000 mph.

Note.

If you are trying to rev to a high rpm eg 7500-8000 rpm, the rpm limit hysterisis can be subtracted from the limit twice. This means with the default numbers your rev limit could become 500rpm lower than expected, this may appear to be a speed limit however it is a rev limit. To fix this problem adjust the hysteresis in scalar auF12252.

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