The application of appropriate excavation equipment in difficult grounds is of crucial importance and consequently improves the performance of hard rock Tunnel Boring Machines (TBMs). The cutterhead is one of the main components of TBMs which is directly involved in the excavation process, and its design can highly affect the cutting efficiency, the overall balance of the head, the performance of main bearing in long term, and the wear of the whole cutting face and muck buckets. This paper mainly focuses on the significant role of a proper design on the cutting efficiency with reference to a TBM tunneling project. Due to existence of very hard and abrasive rocks on the path of Kerman water conveyance tunnel, a new cutterhead was designed to be applied on a second hand TBM. The new cutterhead contains larger 19-inch disc cutters with a new disc cutter layout. Since the new cutterhead was launched following the excavation of the old one in a specific chainage of the tunnel, the performance of the two cutterheads in pyroclastic rocks could be compared with respect to the cutting efficiency, and lower specific energy values were observed for the new cutterhead which is the indicator of a better cutting efficiency in this geological condition.