When to upgrade fuel lines? Reply #15 – January 03, 2013, 04:25:18 PM Evaporative emissions. That's Ford's line on it, at least as far as I can remember. I think there was something about crash standards as it relates to the possibility of a fuel leak also. I haven't had to think about it since school.At any rate, that's not what this thread was for. I feel better about staying with stock line sizes, so thanks everyone for your help. Quote Selected