there is a bunch of destructable cars I found while doing the npc menu, but I can't find them again on the codex. They look normal, and should be changeable by changing the HP in a demo... not sure if this will work, but give it a shot..
Blue sedan, parked V_Mayhem_Vehicle_Car01
Brown sedan, parked V_Mayhem_Vehicle_Car01b
Green sportscar, parked V_Mayhem_Vehicle_Car02
Black sportscar, parked V_Mayhem_Vehicle_Car02b
Red sportscar, parked V_Mayhem_Vehicle_Car03
Maroon sportscar, parked V_Mayhem_Vehicle_Car03b
Blue compact hatchback, parked V_Mayhem_Vehicle_Car04
Green compact hatchback, parked V_Mayhem_Vehicle_Car04b
I don't remember any of these being on fire. try testing HP at different stages. That's about all I can offer.
[edit] found them again, they're under objects, vehicles. I think they are the ones that were parked on the street, so 'vandals' could blow 'em up, like in King's Row.