[UNSOLVED] Question about adding prespawned Vehicles to a map

Hi!
I have a question: I noticed that you could add vehicles to a map that will spawn up everytime you load the map. I spawned up cars in the game, opened the editor and saved the map. The cars did not appear after I loaded the map up a second time. Can someone explain to me how I can make this work please? Thanks.
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I wanted to creat e a group of Nascar cars so I don't have to spawn them up every single time .