Algodoo

Some suggestions
Make the gears heavier and without restitution. that will give you more traction on higher gears. For the spawners, write pos:=pos and add vel:= entity.vel to be sure that the balls spawn in the exact position of the spawner, and don't brake the car. If you want to give color to the balls write color:= [1,0,0,0.5], that will make the balls of red color and half transparent.
You can make the engine stronger by adding density to the spawned balls. Not too much or it will drag it upwards.

I don't know if you already knowed this, but i hope i helped

Thanks you The Linkage, I already knew (not knowed ^^) some tricks (color, density)[that's why I wrote "simple" car] but the other no !!
AND THANK YOU I asked on the forum but nobody answer me to all my questions I will try on my mercedes.