Does a car work faster if it's heavy or if it's light?

light....but if its to light,or the engine is to power full it will brake traction and spin the wheels

There are possibilities of combinations between weight and speed for cars. It works like this: If a car is too heavy, it takes much power to accelerate it. Acceleration varies directly with the force acting upon it and inversely with the mass of the object. In English, this means, the more force you apply to an object, the faster it runs, but the slower it runs when the heavier it becomes. But on the other hand, a light object would not press the tire so much to the road, so you lose traction. The tire won't generate friction on the road. So, to remedy this situation, the practice is to make the race car lighter, but to put a wind sail (or aileron) at the back such that wind pressure will push the car down to the road when running.

The effect of a reduction of mass is to reduce the frictional forces and moments at the bearings. This should allow the motor to rotate at greater speed and drive the car faster.

However the amount of work that the motor does is not very dependent on the speed and the acceleration before reaching the maximum speed will slightly depend on the variation of driving torque with this speed, so it can be either way.

Balance has nothing to do with speed of work but stability does have and it is likely that the lighter car has its center of gravity higher and is therefore less laterally stable.

First try pushing an empty wheelbarrow,then fill it with sand and try pushing it.You will FEEL the differanc in energy needed. Second,ride a bike at 1mph then speed up to 10mph and you will see the aid of speed to balance.

a car work faster if it's light

if cars of equal engine power have different masses,the velocity of the lighter car will be more.