Be in Arcade mode and use the sports car. Some luck is required. You must pick up a decent amount of boost, at least four or five per lap, and use them in the following key areas:
At the first hill at start of the race, if you get boost from the first pickup, use it. Use a second one at the loop de loop. Use the third on the left turn after the loop. Save the fourth for the big hill just before hitting the patch of ice. If you have enough remaining, use one just before the final jump in the track, the area by the candles. Finally, use one as soon as you land that jump. If you are not besting 40 seconds on your first lap just restart.
ACHIEVEMENT - HOW TO UNLOCK Bronze Rumble (10 points) - Get eleven Bronze medals. Can't Pick This (10 points) - Do not pick up any power ups for three laps in "Black Out". 8-Ball (10 points) - Win a pool game without pocketing the black ball. Real fun (10 points) - Finish five challenges with friends on split screen. Treasure hunt (15 points) - Find five golden flags in "Black Out". Loaded (15 points) - Unlock all power ups. Chain racing (15 points) - Finish "Toy Race" twenty times in a row. Alien Hunt (20 points) - Find five golden Aliens in "Toy Race". Gold Struggle (20 points) - Gather all fifteen Gold medals. Hero (20 points) - Finish in first five times in a row against five hard NPC on "Speed Racer". Ultra Fast Food (40 points) - Beat 1 minute 15 seconds on "Fast Food". Silver Fight (15 points) - Get twelve Silver medals.
Disable "Auto Respawn" in the options settings, then go into Arcade mode so you don't need to worry about other cars finishing the race. Start it by yourself:
Toy Race Aliens 1. Directly behind you at the start of the race. 2. At the huge jump in the middle of the track, the alien is on the high track. Use a boost just before leaving the track. 3. On the ground, to the right of Alien #2. 4. Somewhere on the ground. Drive around and you should find it easily. 5. Just before entering the ventilation shaft near the end of the race, on the right.
Black Out Flags 1. To left of starting point, in the bath tub. 2. From the starting line, take your direct left and fall to the ground. Head left and you should see the flag. 3. From Flag #2, go to the top right of the map. The flag is near or under a chair. 4. On top of a chair that has a path leading up to it from the ground level. Take the path and grab the flag. It is very close to Flag #3. 5. Go around the track until you are at the table area with the candles and the wine glasses. There are two power pickups, one on the right, and farther to the left. Go to the top left of this table. Drive off the table heading towards the wall. You should land on a blue ledge near the wall. Follow this wall and drive off in the same direction you have been traveling. You should hit the ground level. From here, turn to your right and you should see the flag.