Which gets better fuel mileage, Speed Density or Mass Air Flow on mild or stock engine cars? I have everything to do the swap, but I don't need to, so I haven't. My old car got decent gas milege, and although it was a 5-speed, it was much better than this car. I am going to convert it to the 5-speed from AOD very soon, and after than I might install my A9L and the rest of the harness, including the 140mph speedo as well as a few other parts.