As others have said its best to step up to atleast 3/8 if the rules let you. My sons Dart has run 11.40's @ 117 with the stock 5/16 fuel line on it. We bought the 3/8 line 3 years ago and he has not put it on yet since it runs so good with the 5/16 line. His Dart does not lay over or feel like it is leaning out. I figure his 400 is making right around 475 to 520 hp. So in many applications 5/16 fuel line will support 500 hp but why take the chance if you can upgrade. Ron