Unfortunately there is no way to prevent cars blowing up. They have a fixed amount of HP and I don't think anyone found a way to increase this or otherwise make them practically never explode.

Very unfortunate if you want to mod the game and make guns more lethal because it also means cars explode sooner.

There was a Free Ride mod that was quite decent though I can't remember the name of it. It let you hire goons you can bring with you as you go around town, as well as introducing different open world objectives. Can't remember all the details but it basically turned an otherwise pointless game mode into a decent one.