[dogscoff]

Try this:

Take normal engines away from pre-warp races. Limit them to a modified emergency movement component. Call it a "system drive" or something. Make it 50kt and very expensive with (for example) movement 4.

Now use the map editor to make sure that all the planets in the start system are more than 4 squares away from the warp points. (In fact this is also possible without the map editor)

Finally make sure that the pre-warp races can't build spaceyard / repair components on ships until they develop warp technology.

The emergency movement component is limited to one per ship and is destroyed after use. This means pre-warp races will be unable to build a ship with a range of more than 4 squares. It will make travelling through their own system rather difficult, but a human player would manage by colonising a nearby planet, building a spaceyard on it and using that to "resupply" (ie repair) their system drives. However, because they can't build mobile spaceyards and all planets are 4 squares or more from the warp points, the player will be unable to leave their own system until they develop warp tech.

The only drawback is that once they have warp tech, your race will have premature access to a 4 movemnt point emergency movement component. The large size and high cost should make it less unbalancing though.

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"Pinky, are you pondering what I'm pondering?"
"I think so Brain but, if you replace the P with an O, my name would be Oinky, wouldn't it?"