Get secret cars and most of story mode
Go to password and enter 446-87-224.You should have new cars, challenges, and story mode levels.

Cheat
Put in the password 496-93-993

Unlock everything
Go to password and type in: 723-83-462

Unlock 2 new cars
In challenge beat both the 4th and 5th levels and two new cars can be unlocked!

Strategy Guide and Level Passwords
Here are some tips on racing Hotwheels Velocity X.

To win races, no matter what car, you must constantly tap the A Button to put on sped bursts. To do this, keep doing high point stunts on jumps to make up the Stunt Points needed to perform the speed boost.

Until you get the car Screamin' Hauler (driven by Slick), always use Purple Passion, as it is the fastest and strongest. To beat Slick, keep using the speed boost and fight him with gadgets, such as the Zapper.

To beat Nitro, you have to perform advanced stunts while using speed boosts to get ahead. If you beat him in a race, but don't get the required amount of points, you will lose. (Oh, yeah. When you beat him, use his Arachnarod car until you get a better one.)

Fastlane is really fast. But she and her cronies are very weak. Your best bet would be to alternate speed boosts and weapons to destroy them and get past them. Oh yes, watch out for their bear traps. When you win, Fastlane's Surf Crate car is fast, but the Arachnarod is still better.

Now for Rupert. Racing him is tough, as he is very smart. Keep using speed boosts with a car with good speed, acceleration, traction, and armor. When you beat him, use his car, Maelstrom, to beat the next boss.

Belcher is a dirty racer. When racing him, blast away at him and his cronies while using speed boosts to get him. Watch out for his shortcut move!

To beat Otto and MetaCog is fun. Use Maelstrom to beat all the fake MetaCogs, then go after MetaCog. Otto and MetaCog will use their prototype energy shield to shield themselves against all of your attacks. To hurt Otto, stick by him so that MetaCog will bump him, damaging Otto. Then Otto will use his Otto-sizer. This shrinks you every few seconds and makes him bigger. Keep making MetaCog bump him until you win. Then you will get the ultimate Hotwheels car, Shadow Jet.

Here are the passwords for levels. I'm not sure if they will help you unless you've played the levels before.

Level 1 123-17-543
Level 2 143-24-813
Level 3 141-38-985
Level 4 249-48-723
Level 5 294-16-277
Level 6 457-51-438
Level 7 112-86-545
Level 8 447-65-112
Level 9 368-54-466
Level 10 718-59-438
Level 11 363-95-545
Level 12 373-65-848
Level 13 171-49-211
Level 14 373-59-216
Level 15 373-62-927
Level 16 718-42-276
Level 17 358-59-355
Level 18 478-68-254
Level 19 573-77-683
Level 20 188-58-352
Level 21 766-46-341
Level 22 187-98-394
Level 23 188-12-234
Level 24 786-84-747
Level 25 466-59-979
Level 26 447-58-369
Level 27 447-62-191
Level 28 614-81-432
Level 29 641-18-239
Level 30 399-68-584
Level 31 662-84-635
Level 32 476-63-843
Level 33 616-67-341
Level 34 384-97-475
Level 35 363-13-298
Level 36 521-71-135
Level 37 543-17-658
Level 38 782-57-387