From this timing diagram it is clear that the total execution time of 8 instructions in this 6 stages pipeline is 13-time unit. The first instruction gets completed after 6 time unit, and there after in each time unit it completes one instruction.

Without pipeline, the total time required to complete 8 instructions would have been 48 (6 X 8) time unit. Therefore, there is a speed up in pipeline processing and the speed up is related to the number of stages.