How to 3D print a surface model?
Maybe 1st of all try to write nicknames correctly (will be helpful to find model)..
If you tell about https://grabcad.com/library/bmw-m6-3 , than remember in what program you are working - SOLIDworks
You must sew surfaces, and make the body solid
checkbox = make solid
As you can see now it's solid
Just like this one you must do with whole body.
Make new surfaces for that detailed view, that you want