If you want different fields to be visible depending on the dropdown value, you would either set conditional formatting on each field which would control whether to hide or not depending on the drop down value or you could have various sections for each permutation. Then you could use conditional formatting on the sections and hide and unhide depending on the value of the dropdown. The best approach would be determined by the complexity you need.
If you just need Year to hide for certain entries then I would just put formatting on the year field.
If you need a different layout for each car group then I would go with sections.