Help identify this white and medium grey ship section
Based on Engine 3X3X6 in white, this is from 7166-1: Imperial Shuttle



Or as Syberion mentioned it can also be 
7264-1: Imperial Inspection
 



Which has almost the same build. The only difference I could find is the color of the 6 x 12 plates on the bottom of the build.


7166: Dark Gray Plate 6 x 12
7264: Dark Bluish Gray Plate 6 x 12


Based on the photo, I think its Dark Bluish Gary so it's 7264.

If you still have the minifigs for this set they will also tell you which set it is, as 7166 had the yellow faced figures and 7264 had the flesh tone figures.