Only GM Racing speedos, the LRP SPX Stock Spec and some Tekins have this option.
If you run stock classes with anything slower than a 9.5 it will be a lot(!) faster but feel quite unlinear on the throttle which doesn't really matter that much as the motors are fairly soft to begin with.
If you run modified motors with the variable timing programs it will be near undriveable as the unlinearity becomes more pronounced the lower the amount of turns.
Only worth it if you run stock.
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