The SD38-2 and SD40-2 shared the same basic superstructure, since they used the same 16-645 engine (in Roots-blown and turbocharged form respectively); the long hood was 18 inches longer than the SD38 and SD40, but since the increase in frame length was even greater, the SD38-2 and SD40-2 had even larger front and rear "porches" than the earlier models.