These are different phrasal verbs. "To get out of (something)" means, variously,
- to exit ("She screamed at me to get out of the house")
- to avoid ("You can get out of the meeting by telling the execs that you have a report due")
- to remove ("Why were you out running in the rain? Get out of those wet clothes!")
- to benefit ("You can get a lot of money out of this deal, if you get in early)
- to persuade or interrogate ("Fred, see what information you can get out of the suspect")
and others. Meanwhile, to "get out (something)" can mean:
- to leave ("The police stormed the office and told us all to get out")
- to clean ("This new detergent will help get out even the toughest stains from your clothes")
- to take out ("Please get out the flour and the sugar from the pantry?")
- to reveal ("If word of this gets out, we're in a lot of trouble")
- to disseminate ("Help us get out the word to vote this election")
Because these verbs have different meanings, it's important to memorize them as if they were separate verbs, and learn to use them in the appropriate context. Yes, certain (British) dialects do drop the prepositions from these phrasal verbs, but unless you also use the other phrases characteristic of the dialect, it won't sound right and can be confusing to the listener.
As in your example, "Get out the car!" to mean "quickly exit the vehicle" makes sense when issued in the right context. By itself, however, it sounds like you're asking me to take out the car from something like a garage, so we can go for a nice drive.