163 has an independent fuel burn. You can make Fuel burn 100 times as fast as it does and 163 will have same flight time.
Go offline, Turn wind on with a full uplift (127mph uplift) for all alts. When you get to a certain alt, you can see that the sun is a 2d object in the game. Then if you want to break the speed of sound turn the wind off, turn your engine on (163) and go straight down.