Help with retopo problem from obj

i have attached a model that was imported from a turbocad using obj format but it seems to have shading problems between the 2 curved sections could anyone explain what the problem is orsugest a good solution? remesh advice.blend (638.4 KB)

Recalculating outside by shift N seems to do the trick here as far as I understand. It was probably because of the face orientation as you can see in the second image