Drifting in Forza 4 is stepping up its seriousness with a BC Racing sponsored event that allows you to win real prizes and parts for your virtual performance. The three judges include Formula Drift drivers Chelsea DeNofa, Jeremy Lowe, and Patrick Goodin who even released a 10 minute drivers meeting video walking you through the rules of the game and the virtual track Iberian Mini Reverse. This drivers meeting video can be found here.
Rulebook wise the game is pretty simple which limits you to RWD cars only. Engine, suspension, and tire modification have zero restrictions for this Forza contest. However, no positive camber is allowed with your suspension tuning of the vehicle. You also must run the BC Racing logo which is available in the storefront. Below is a link to the complete rulebook and how to enter and win free stuff.
Read the Rules for the Virtual Drift Cup: http://www.bcracing-na.com/virtual-drift-cup/rules-and-regulations/