We introduce non-acyclic $PGL_n(mathbb{C})$-torsion of a 3-manifold with toroidal boundary as an extension of J. Portis $PGL_2(mathbb{C})$-torsion, and present an explicit formula of the $PGL_n(mathbb{C})$-torsion of a mapping torus for a surface wit
h punctures, by using the higher Teichm{u}ler theory due to V. Fock and A. Goncharov. Our formula gives a concrete rational function which represents the torsion function and comes from a concrete cluster transformation associated with the mapping class.
