Question about shift mechanics

Am I missing something here? So I've been trying to race against the ghosts of top level players in the time attack mode and I've noticed that after getting off of the starting line somehow there car gets a sudden burst of speed and takes off. I was wondering if this game has some sort of "perfect shift" mechanic or something. I just don't get how they car reach there too speed so quickly.

TLDR: I'm aware that if you hold L1 at the right time during the start you can get a lunch boost. I just want to know how top players are getting to their top speed so quickly after the fact.