A Perfect Start only happens when the speedometer needle is in the green section before the race.
In several game modes that include Time Trials, some Public Events and some races in Team Events, it is possible to perform a Perfect Start. A Perfect Start allows one to gain a small acceleration boost at the beginning of a race.
Process
To perform a Perfect Start, one must rev the car's engine during the countdown of the race by holding the accelerator pedal, until the speedometer needle is sitting within the green section. As the countdown ends and the announcer declares “Go!“, the green display glows up in a brighter green on the gauge.
With other tuning parts
With the “Start Boost” tuning part equipped, a Perfect Start can trigger the Start Boost’s rocket power, increasing the acceleration boost. However, the Start Boost cannot be activated in Adventure mode.
If one has the "Nitro" tuning part equipped, a Perfect Start will charge half of the Nitro boost. One can also charge half of the Glider's Propeller Boost after performing it.