My slightly different solution for this, being completely unable to get the timing right
You can buy (using this term loosely!) "Mod Pods" from the Start screen, for 10 credits (these are unlocked in-game regularly, I don't think you can or need to pay cash for them).
These will unlock car parts, and sometimes boosts.
Including "Race Boost - get an automatic Start Line Boost"!Side note - this is luck-based, I unlocked some within 200 credits
So, my guide;
1. Buy some Mod Pods, until you unlock "Race Boost"
2. When you load an event, on character select screen pressing
bring up "Select Bonus Box"
3. Select "Race Boost"
4. Start a game, the achievement will automatically unlock when you boost off in the race
Let me know any queries or suggestions