This is the only way to get unlimited health on crackdown.

First you need some sort of internet connection for your Xbox 360 and once you have the internet on the Xbox 360 you can go to the far left tab wich says Xbox live market place and you go to the game store and select the all games category because Crackdown is fairly old, and the list is in Alphabetical order. Scroll down until you find Crackdown the click it the you should see a lot of results. All you need to do it find the one that say "Free For All Pack" select it.

This pack will unlock the keys to the city function in Crackdown, which means you can have unlimited health, unlimited ammo, all vehicles impounded, Super Speed, Super Endurance, All Skills Maxed out; including the ability to spawn Explosive barrels, Ramptrucks and Various Agency Vehicles.

But unfortunately there is a catch to this - The Keys to the City function disables Achievements, Saving, and LeaderBoards.