The clutch switch allows the driver to make gear changes without having to back off the accelerator. When the Traction control sees that the switch has opened or closed a rev limit is imposed, allowing the driver to keep the throttle wide open. This allows for faster gear changes and quicker acceleration times. Tests have shown up to 0.1 seconds can be gained per gear change.
Fitting a switch
DO NOT apply the 12 volt feed PIN 20 from any clutch switch which may already be fitted to the car, hardware damage WILL result. An independent switch should be fitted between PIN 20 and GND, as below:
The switch needs to be mounted on the clutch pedal, in a place where the contact makes or breaks when the clutch is depressed. A suitable switch is a motorcycle rear brake switch, this is a plunger type switch that can be adjusted to switch at the biting point of the clutch. Rear brake light switches can also be used. These have not proved as successful on road cars as by just resting your foot on the clutch pedal is enough to switch the rev limit on. Another method that can be used is a hydraulic switch, these are easier to install on race cars.
The chosen switch is wired up by connecting one side of the switch to GND and the other to pin 20 on the traction control loom.
The traction control is set up for a normally open contacts, this can easily be adjusted in the software by changing the following in the launch control menu.
Setting the Clutch Switch REV Limits
These rev limits are similar to the rev limits used for the launch control function except they are operated whilst the car is moving. The difference between the soft and hard cut is set to 250 Rpm.
The rev limits will need to be set 1000-500 Rpm lower than the cars own rev limit. The full throttle shift should be smooth, so adjust the rev limits to get the smoothest change.
Testing the Clutch Switch
The easiest way to test the switch is to drive the car on a quiet road. While still rolling place the car into neutral, press the clutch and raise the revs up to the new rev-limit. By placing the accelerator hard down the car will settle on the new rev-limit, until the clutch is released.