To make clear the influence of a torch jet flow on the combustion process, a laser Doppler anemometer (LDA) is used to measure the mean velocity and turbulence intensity in a spark ignition engine with an unscavenged prechamber connected to a main chamber by a torch nozzle of different area sizes. The test engine is operated at a constant speed of 16.7 rps (1000 rpm), a constant volumetric efficiency of 80±2% and MBT for each torch nozzle area under firing as well as motored conditions. The LDA system is a dual beam forward scatter type, and its signals are acquired quickly and stored in a memory through a frequency tracking system. The LDA measurements are made at several locations in the main chamber.In the present paper, the turbulence is defined as the high frequency component of velocity above a cut-off frequency (0.75 kHz), and a cycle resolved analysis is performed to obtain the mean velocity and turbulence from individual cycle. According to contour maps of the mean velocity measured under the motored and firing conditions, the mean velocities during the compression stroke are almost the same in all patterns. During the expansion stroke, however, the mean velocity and turbulence intensity in the main chamber are strongly affected by the torch jet flow, which is also considerably influenced by its cross-sectional area and operating conditions.