I can't explain it much better than I already have m8, so I think you will just have to do some "trial and failure" to understand how the engine effect works!
And no... the flame effect, whether it's normal enignes or cruise, don't care if there's a trail or not so you can use any effect you want! Try putting in a weapon effect and see what happens! Some of them actually looks awesome as engine flames! Hehehe...
Play around with the effects... All you can achieve is something that might look great, stupid or a crash and in the last two cases just have a backup of the old code ready!
And no... the flame effect, whether it's normal enignes or cruise, don't care if there's a trail or not so you can use any effect you want! Try putting in a weapon effect and see what happens! Some of them actually looks awesome as engine flames! Hehehe...
Play around with the effects... All you can achieve is something that might look great, stupid or a crash and in the last two cases just have a backup of the old code ready!