Instantaneous gas velocities inside the combustion chamber, cylinder and inlet port of a motored 4-stroke engine have been determined using a constant-temperature hot wire anemometer. The measurements were made with both stationary and moving probes, the latter being operated by means of a traversing mechanism driven from the piston of an adjoining cylinder. With the moving probes, it was possible to study the flow close to the piston crown throughout the induction stroke. The probes were calibrated in a steady gas stream and their response checked under transient conditions using a shock tube. Cylinder gas flow readings were obtained at two speeds of rotation of the engine and a masked inlet valve was used to create varying degrees of induction swirl.