Thanks for JimbotUK
for the tip, there is currently an event with a guarantee 3-star car. Time to get it.
It is a spotlight event where you have to dominate the last part of it (6) to win the car. You need also to play on medium or hard.
The bad news are:
1) You spend a lot of energy, the first two parts require 1 energy for evey node, 3rd and 4th, two energy and the last two, 3 energy. You must have a lot of refills or you will have to wait a lot.
Thanks to eberthold
that spotted that the game has been patched and the following are not true anymore.
2) Altough, the medium event seems easy, I'm currently stuck in the car before the final boss. It's a lv 540 car, but it runs like a 640. I can't even start to chase it with a better.
After like 20 attempts, i changed the car and manage to win it.
It is bad AI implemented, the car has different results with different cars, so try all you cars and see which one goes best against him. The final boss car, however, is a normal car which should pose no problem.
3) The achievement seems to be glitched, people are complaining that it is not unlocking after winning the car.
Before dominating, on your victory you will also win a car card and 150 gold which you can use to buy another car. Those are chances to get the 3-star car too.
Thanks for MANIAN 3D
for the info.
Another good option to get a 3 star car is from daily cards, but that is totally random, I never got one.