[Suicide Junkie]

Making fewer engines move ships at the same speed would push that 24-MP escort well beyond the 30-MP barrier in simultaneous games. There would be a wall beyond which adding more engines only improves your combat speed (from 15 to 20 or higher) and your interplanetary speed would be stuck at 30.

As for making a larger standard engine (more powerful, but fewer fit on a ship, so it balances out), that could be done, but it would require reworking the AIs.