This one can be a little tricky because you need some skill and track knowledge if you want to get this achievement but even if it's not a clean lap it will count for the achievement.
I recommend googling to get a tune for your specific car and track if you need to get less one or two seconds on your fastest lap but if your time is 2 28 or higher it's better to go play the game for a while and get acquainted with the physics of the game.
Happy Hunting