Taken from another forum I visit...
"It may look cool on "The Fast and the Furious," but modifying your exhaust to shoot out flames is not only corny, but a dangerous fire hazard. Besides, you don't really want to be known as the Einstein who took a questionable movie idea and tried to make it happen in real life. If it were that easy then I would be able to hop onto any old Air Force Base in Europe, jump into a standing, fueled, and armed F-16, and go save my Dad from a Middle Eastern POW camp (and I would also be able to fire a sidewinder from an aircraft on the ground!) This can't really happen, and neither should a flaming exhaust. (For those of you unaware of the movie I reference, go rent "Iron Eagle.")"