Start a race in Quick Race mode and choose the car you want to unlock. Start the race, but quit before finishing it and save your game. Now load your save file and head to Career mode. You'll find the car available, though you still have to purchase it from there.
When you are at high speeds and take turns that the game would not expect you to do, you will you ride on a horizon. It is black and slightly orange. Be careful as you can still crash. It looks like your car is going so fast that the map area was not mapped. This usually happens on the last sprint for Ex on the last piece of territory.
Unlock the Super Composite hood and spoiler for the following cars by winning the corresponding Bonus Part Challenges:
HOOD/SPOILER - CHALLENGE Porsche Carrera 4S - Bonus Part Challenge 1 and 2 on Rank 5 Porsche Carrera GT - Bonus Part Challenge 1 and 2 on Rank 2 Chevrolet Cobalt SS - Bonus Part Challenge 1 and 2 on Rank 13 Chevrolet Corvette - Bonus Part Challenge 1 and 2 on Rank 6 Mitsubishi Eclipse - Bonus Part Challenge 1 and 2 on Rank 11 Ford GT - Bonus Part Challenge 1 and 2 on Rank 3 Lamborghini Gallardo - Bonus Part Challenge 1 and 2 on Rank 4 Volkswagen Golf - Bonus Part Challenge 1 and 2 on Rank 15 Mitsubishi Lancer - Bonus Part Challenge 1 and 2 on Rank 9 Mazda3 - Bonus Part Challenge 1 and 2 on Rank 14 Mustang GT - Bonus Part Challenge 1 and 2 on Rank 10 Mazda RX-8 - Bonus Part Challenge 1 and 2 on Rank 12 Audi TT - Bonus Part Challenge 1 and 2 on Rank 7 Subaru WRX STi - Bonus Part Challenge 1 and 2 on Rank 8
-Buy the Lamborghini Gallardo when you are able to. Upgrade all of its performance upgrades. It will almost be full. Try to get the handling better than the speed or it will have no effect. You should win all events and defeat the Bosses easily.
-Get the Audi TT as soon as possible and tune it up as far as possible. Everything will be almost full. Then, buy the Gallardo as soon as possible and tune it up as much as possible. It will be one of the fastest cars available.
Activate the following cheats by starting a new game and entering any of the corresponding codes as a profile name:
CHEAT FUNCTION - CHEAT CODE All bonuses & $500,000 - "!mr. blonde" All tracks, cop cars in Tuner Takedown tracks, and $100,000 - "!get-set" All cop cars in Tuner Takedown and $100,000 - "!bacon" All performance and visual upgrades and $200,000 - "!tuner-well"
-When you are in a cop chase and the police have you pinned against a wall, press Select to get into the center of the street and drive off as fast as you can to make the bust meter go down. Be careful when doing this in higher levels since the bust meter fills up a lot quicker and you must be very quick with what you do.
-Drive very fast (about 220 mph with nitrous) and when you reach top speed and are on a wide street, get to the far right and swerve (press R) 180 degrees. This will catch the police off guard, causing them to slowly turn around and decrease the bust meter.
Unlock the following cars by defeating the corresponding opponents:
CAR - OPPONENT Porsche Carrera 4S - Ming Porsche Carrera GT - Toru Sato Chevrolet Corvette - Kamikaze Mitsubishi Eclipse - Big Lou Ford GT - JV Lamborghini Gallardo - Webster Mitsubishi Lancer and Subaru WRX STi - Earl BMW M3 GTR 1 - Ronnie BMW M3 GTR 2 - Razor Ford Mustang GT - Baron Mazda RX-8 - Izzy Audi TT - Jewels
Try to get high speed. Then drive near other cars and you will get near misses. When a cop car is waiting for you, drive quickly in front of it. When the cops try to slow you down, crash them to get pileups. You should reach Heat level 10 in a minute.
Unlock the following cars by defeating the corresponding bosses:
CAR - HOW TO UNLOCK 911 Carrera S - MK Aston Martin DB9 - Jenna Carrera GT and Lamborghini Gallardo - Clutch Chevy Cobalt SS and VW Golf GTI - Marcus Chrysler 300 and Pontiac GTO - Layla 1 Firebird, Toyota MR2 and '67 Mustang - Poorboy Lotus Elise and Mustang GT - Steve Mercedes SL65, Corvette and Ford GT - Scotty Mitsubishi Eclipse - Sly Nissan 350Z - Daemon Pontiac Solstice - Striker RX-7, Skyline GTR and WRX STI - Buddy RX-8, Toyota Supra and Audi TT - Layla 3