BBi intake manifold torque

I removed the upper portions of my intake manifolds, in order to get at the WURs. I am now installing them back. They have 1/4 inch rubber gaskets, with metal spacers, between them and the lower intake manifold.

The studs are 8mm, with 13mm nuts. I am assuming about 15-18 ft/lbs. Is this correct, or do the rubber gaskets call for less torque?

Thanks.