Is there a way to take control of the backfire trigger? At the moment it seems to just go off after heavy engine braking but I want to control the exact conditions when this happens. Is it possible in 3d max to control the animation trigger?
You could try to ask the Devs, that are replying here in the Forum, if they can tell you what it needs to activate the Backfire. But i suppose that you'll get no Answer.
You can constantly trigger Backfire by rapidly pressing Pit speed limiter button On and Off, it works even if the car doesn't have a limiter. Although it probably not the exact function you are looking for, it can be used to test backfire visual effects.