There are two main differences between metallic car paint and the standard car paint.
Metallic paint is more reflective than standard paint; it has less diffuse and more gloss. For the base layer, increase the Reflections and Glossiness. Various paints can be very metallic (see example photo above) or somewhat less metallic… in which case, you would simply lower the Reflection amount.
The second difference is that there are tiny, reflective flakes in the paint that reflect the light at different angles. This is taken care of by the Flakes layer in the CarPaintMtl. There are a couple of things to keep in mind: usually the flakes are very similar in color to the Base layer, but a bit brighter. Mapping type should be set to triplanar from Object XYZ to avoid relying on the object’s UVs. The scale and size might need to be adjusted for different models, this one is tweaked for the example scene.
