From what representatives from some websites tell me and from reps from my local ford dealer say. You don't want to modify the thermostat or other things that involve the engine internals in some way. In other words
- no cylinder heads mods
- no crank or bore mods
However it safe to say that you can modify the exhaust and intake (CAI) but I would recommend you don't do a lot to it, especially if its a 3.9L.