Okay, i want to point out an idea. We all know Gmod racer, why not
Use evocity2 and make the gamemode randomly choose the roads that will be used in the race or just make some pre made tracks choosen randomly.
Use good models and generally modificate the gamemode to have not just upgrades, but new cars and some more customization, some more balance.
Make players divided by car/level and only place people with similar car/level in one race for balance?
Not going to be easy i suppose, just an idea.