The Transanatolia is perfect for 4x4's.  The routes offer a big variety with a lot of gravelroads, combined with mountain passes with rocks and stones. September can be quit warm, something to keep in mind. Good navigation saves a lot of time and makes all the difference.

Requirements

The requirements for your 4x4 are not really high, there's no FIA regulation to keep in account. A racelicence is not required.
A rollcage, raceseats and a five-point harness are not obligatory, but always good for safety off course and a good investment.
Good protection for the underside off the car is definitely an advantage.

With a technically good prepared car, with good tyres and suspension, you're ready to subscribe.

What is required: 2 sparewheels, kinetic and normal recovery rope, proper jack, a minimum of 10 liters drinkable water, gps (Garmin with min-usb connection) a good roadmap of Turkey and first aid kit.