Boost:
Hold Select while choosing an area selection at the map screen. Release Select 
when the auto-pilot engages. Start a race, and you will be able to use a boost. 
Note: This can only be done with cars that do not already have a turbo. 

Foggy weather:
Select time attack, free run, or vs. battle mode and choose rain. 
Hold L2 while you are selecting the track starting point to make it foggy. 

Snowy weather:
Select time attack, free run, or vs. battle mode and choose rain. 
Hold L1 while you are selecting the track starting point to make it snow. 

Stormy weather:
Select time attack, free run, or vs. battle mode and choose rain. 
Hold R2 while you are selecting the track starting point to make it thunder. 

Switch engines:
Get over 1242.8 miles (2000 km) on the odometer on a car to unlock the ability to 
switch engines on that specific car. Successfully complete 100% of the game to 
switch the engine of any car. 

Natural Aspired Boost 
This must be done with a NA car, meaning non-turbo cars. At the map screen while 
choosing an area to enter, press and hold select. Enter the area you choose while 
holding select. Keep holding select through the loading screen, and up until the 
auto-pilot feature comes on. Begin a race, and now, you can use the boost. 
NOTE: 
Use the boost wisely because the water and oil temparature will rise drastically. 

Mileage Glitch 
Win or lose against any rival and when it comes to the "Free Run", "Replay" 
and "Save Replay" screen, take the cd out, close the disc tray and hit "Free Run". 
The road and music will disappear and you will be on Auto Pilot. You will realize 
that you're mileage will go up. Use this glitch to unlock the engine swap easily. To 
continue, just put the disc back in. 

Swapped Natural Aspired engines available
L4, L6, V6, V8, and Rotary engines. 

Swapped turbo engines available
L4, L6, V6, V8, F4, F6, and Rotary engines 

Turbo, Natural Aspired engines 
Drive 1242 miles on ONE car, on that ONE car, or complete %100 of the game to 
use with any car