Looking for good engine noise and a VERY wide range of difficulty settings

Hi all.

Any tips on an Xbox-360 racing game with VERY wide difficulty settings? Like the equivalent of those lane bumpers in bowling? I've got a 4-year-old who loves Asphalt 6 Adrenaline on my iPhone -- he loves the engine noises and unlocking exotic cars. So I'm afraid MarioCart knockoffs won't do it for him. But it would be nice to find a game that takes him more than 10 seconds between crashes.

An ideal game would have split-screen multiplayer, and split difficulty settings such that he can't really go off the track, but I can set up so that I have to really work to beat him.

And it should be fun.

If it's not the latest iteration of some franchise, that's OK.

Anything fit my bill?

Thanks all. Take it easy.

NFS Shift ( although I can't remember if it has split screen )

The Dirt series have a very wide range of difficulty because you can easily change the difficulty of the opponents and the handling of the cars separately. More specifically, try Dirt 3.