  In this paper most of the classes of G2-structures with Einstein induced
metric of negative, null or positive scalar curvature are realized. This is
carried out by means of warped G2-structures with fiber an Einstein SU(3)
manifold. The torsion forms of any warped G2-structure are explicitly described
in terms of the torsion forms of the SU(3)-structure and the warping function,
which allows to give characterizations of the principal classes of Einstein
warped G2 manifolds. Similar results are obtained for Einstein warped Spin(7)
manifolds with fiber a G2 manifold.
