Particle Image Velocimetry (PIV) was used to make gas velocity and turbulence measurements in a motored diesel engine. The experiments were conducted using a single-cylinder version of the Caterpillar 3406 production engine. One of the exhaust valves and the fuel injector port were used to provide optical access to the combustion chamber so that modifications to the engine geometry were minimal, and the results are representative of the actual engine. Measurements of gas velocity were made in a plane in the piston bowl using TiO2 seed particles. The light sheet necessary for PIV was formed by passing the beam from a Nd:YAG laser through the injector port and reflecting the beam off a conical mirror at the center of the piston. PIV data was difficult to obtain due to significant out-of-plane velocities. However, data was acquired at 25° and 15° before top dead center of compression at 750 rev/min. Experiments were also conducted in a turbulent jet for comparison with previous jet measurements made with other techniques. It was found that high and low estimates of the turbulence intensity can be obtained from limited PIV data, and that length scales can be found by computing the turbulent dissipation and using kε turbulence model relations. In addition, the size of the eddies visible in high-pass filtered PIV data, and the size of vorticity concentrations were also found to be representative of the turbulence integral length scale. The engine PIV data was compared to flow and turbulence predictions from the multidimensional KIVA-3 code. Reasonably good agreement was found between measured and predicted turbulence intensity and length scales in the engine.