first of all, thanks for your free feedback. In that first moment I was only trying to evaluate my geometry, but I appreciated the indication of both cases, they helped me a lot with Snappy Hex Mesh setup (which I am not very experienced with).
Taking advantage you already seen this project, could you give me some hints on what is going on now? If you take a look at the same project, you will see that the mesh is much better, with specific regions refined regarding to physics as it should be. However, it seems that some regions were not recognized by the “Feature Refinement” feature, as you will clearly observe (chassis tubes mainly). Another thing wrong is that the engine surface may have some hole, because its interior was meshed. This I would guess at a first glance that changing the toleration factor, then even if engine’s surface has some gap I could overcome this (as explained for me already at CAD issues for CFD analysis). However, as I did never do this, any help would be welcome.