Hello and welcome!
These are beautiful!
Dave (Bushcraftonfire) is correct, you have good contrast but it could be "tweeked" for a more professional/realistic touch.
The dimensions on the car facing seem a wee bit off, am I the only one who sees it? (I could be wrong so wait for other opinions on that)
Really really nice work. Did you scan these? It almost looks like they are scanned and I personally feel that sometimes a scanned piece doesn't translate as well. I can't help but wonder if that is part of your contrast issue?
I also wonder if maybe blending and smoothing (with a blending stick) out the metal portions of your cars would give them a more "metal" look if that makes sense? We have a member (Blue Angel) who does a lot of cars and motorcycles. Beautifully done work and maybe viewing some of his art will give you an idea of what I am trying to convey.
Overall though I think you have done an outstanding job! I look forward to seeing more from you.
Excellent drawings! The only thing I would work on as others have said is the shading, try a blending stick to improve the texture of the car surface so it appears more smooth and realistic. It just takes practice. Have you also tried different grade pencils and paper, it helped me.