Hi Riko, I have had a quick play with it and this is what I came up with. If this is a concept car wing, then do the wing surface(s) first, joining as needed then trim the wheel arch. So here's what I did ... Joined the gap in the wheel arch, then a 3 point curve which replaces your original dividing line from top of the arch to the top of the wing. This new three point curve creates a subtle blend curve using the original starting position as point one, point two is the mid point of the line added between the arc end points and the third point of the curve is placed on where the original dividing line touches the top of the arch. You can now join the curves at the bottom of the shape to create a new single curve, do the same to the top curves of your wing, and then you can use the remaining two curves to create your shape topology ready for networking. Click network, then use your original arch curves as the trimming lines, remove the inner surface and there you will have it. The shape does not totally marry up to your original arch curves, but you may know how to make it more accurate to your needs.
Martin
Edit ... Oooops forgot to give you the new surface  Sorry
Martin
