[US_GRANT]

You can't disable it because it is in the SFS files, however, you can install the gray curving smoke trail mod from 1.2 by creating a mods folder in your HSFX 4.X install and edit the SmokeBlack_BuletteTrail.eff file and change the LiveTime from it's current value to 0.0 and that will efectively remove the smoke from the game, but it will do it to all smoke tails, I believe. I have not testested it though, so do so at your own risk.