78. As shown in the figure, a cylindrical glass contains a conical iron block, with the base radius and height of the glass and the iron block being equal. Now water is poured into the glass. When the water level is $\frac{2}{3}$ of the glass height, an additional 260 cubic centimeters of water is needed to fill the glass. The volume of this conical iron block is $\qquad$ cubic centimeters.
Answer: 270