This is actually an old name. The trouble is that people who use it today don't know its derivation--it's not "Porsche," after the car, but "Portia," after the heroine in Shakespeare's Merchant of Venice. Somehow the inner-city denizens heard the name and thought it referred to a vehicle, and so misspelled it. There are pretentions among people of all races, I guess, not just the white Americans.