Create your own race in LA. On the far southern island place a checkpoint near one bridge and the other checkpoint near the other.
If you test the race, you'll see that all opponents take a certain shortcut. However, they aren't fast enough and will crash into a wall and stay there, leaving you to win the race. Over and over.
This might be boring but it works. Start a Detonator Battle with teams of 3 cars.
If the game starts, drive straight to the delivery point without picking up the Detonator. Wait there and make sure you know which team's got the bomb.
As soon as the enemy gets the bomb, stay there 'till the last minute, then drive into him/her to destroy the Detonator, probabily using a pickup.
If one of your team picks up the Detonator, head straight for him immediately to help him, and hope that your other team member is enough help 'till you arrive.
If you started a game with 2 cars per team here there is no-one to help your friend but you. You are waiting on the finish however so your opponents have probably beaten the Detonator before you arrive.
I hope this will be helpful,
Go to the Options mode > Cheat Codes then type "howfastcanitbe (0-9)".
Go to the Options mode > Cheat Codes then type "octane".
Go to the Options mode > Cheat Codes then type "yerbamate".
Go to the Options mode > Cheat Codes then type "rimbuk".
Go to the Options mode > Cheat Codes then type "theparrot".