I would really recommend adding more fixtures, especially some vents to the side of the grill to fill in some of the large blanks spaces you have on the front of your cars. Also, trying combining different headlight fixtures to make some more unique shapes rather than just sticking the stock ones onto the body.
For a pair of 2017 model cars that aren’t supercars or hypercars, fuel economy figures in the mid-low teens (or even single digits in the race versions) is simply not enough, and the styling is, quite frankly, underdone. Still, there is enough room for improvement to make these cars much better than they are right now.