Rewards can be seen in the game.
Race tips can be found here.
Official information for FAQ are here.
To get any reward you have to finish lap 4 to qualify. If you win and reach lap 15 you will still only get one heroic dragon when the race ends.
Lap 13 > 14: Heroic orbs chest x2 (8hrs)
Lap 16 > 17: 120 High Voodoo Vampire orbs x2 (8hrs)
Lap 17 > 18: 40 High Robo orbs x2 (8hrs)
Lap 19 > 20: 50 L Joker orbs chest x2 (8hrs)
Lap 24 > 25: 50 H Joker orbs chest x2 (8hrs)