Here is the full list of all 45 FlatOut 4: Total Insanity achievements worth 1,000 gamerscore.
Burnt nitro continuously for at least 5 seconds in a race
Emptied all your nitro for the first time from full to empty
Upgraded a car once
Completed your First Cup in Career Mode
Destroy 50 opponents (offline)
Jump at least 100m long with your car
Slam 100 opponents in online races
Complete your first race in Arena Mode
Win a race in Derby, Classic, AllStar classes
Buy at least 2 cars in each class, Derby, Classic and Allstar
Drive a total distance of 500 miles
Destroy 20 Opponents Online
Keep the flag for 66 seconds in Keep the Flag Game Mode
Score over 100,000 in a race
Recover the flag 10 times in the Keep the Flag Mode
Kill Three opponents in the same race (offline)
Make the perfect score in a stunt game
Use the 4 different weapons in Assault mode
Destroy 2000 breakables
Win 15 races in Arena Mode
Upgrade an AllStar car at the maximum
Destroy your first opponent (offline)
Purchase all cars of the game
Hit 3 cars with the same activated weapon in Assault Mode
Win 20 races in Assault Mode online
Win 5 races in Assault Mode online
Complete FlatOut Mode with all gold
Earn 123456 cash in Career Mode
Finish consecutively 10 times on podium in Career Mode
Win 10 online races
Win 25 online races
Get all available skins for a Derby car
Destroy your car for the first time
Beat a Time Trial with gold in Career Mode
Complete FlatOut Mode
Complete Career Mode
Complete all stunts with gold in FlatOut Mode
Complete all stunts with bronze in FlatOut Mode
Be both Survivor and Eliminator at the same time in 5 Arena Deathmatches
Win a race without crashing (100% Full HP)
Eject your driver 100 times
Win a race in Assault Mode
Win a race with the maximum car parts on your car
Win an online race
Wreck 5 vehicles during a round in Arena Mode