[Suicide Junkie]

All engines burn their "supply use" about of supplies when the ship moves a square.

So if your engines take damage, you'll use up less supplies to get where you're going.

In stock, if you have 4 Ion drives, you spend 10+10+10+10 = 40 supplies per sector.
If you have 1 quantum drive, you spend only 10 per sector, and still travel 4 per turn.
If you use 4 quantum drives, you get a speed of 7, and use 40 supplies per sector.

Just add up the supply use of all your surviving engines, and you'll spend that every square you move.