I believe the ITE rules vary from division to division. The rules in SOWDIV are very simple and short...

Cars eligible for ITE are production based cars with fenders and doors that are not currently eligible for any other SCCA club racing class. Cars entered in ITE must meet minimum safety standards of the 2008 GCR and Improved Touring Category Specifications, ITCS, including all items in Section 9.1.3, ITCS. Suitability of any car for ITE is subject to the approval of the Chief Steward and Chief Scrutineer. The maximum engine displacement for normally aspirated cars is 3,500 cc. Turbo-Charging or Super-Charging is allowed with a maximum displacement of 2,500 cc. Rotary engines are limited to two (2) rotors.

http://www.sowdivscca.org/rules.aspx