A new instrument to measure the swirl of a cylinder-head on the steady flow rig has been developed. Basically the instrument consists of a cylindrical piece which is placed under the testing cylinder, forcing to pass the air through a series of holes, which are radially perforated at the base of the piece. The air leaves the piece with radial direction so that the angular momentum of the air is proportional to the speed of the instrument, which rotates because of the swirl. A simple measurement of the rotational speed allows the calculation of the outlet angular momentum. Then, the angular momentum in the cylinder can be estimated by adding the friction torque to the measured angular momentum at the instrument outlet. This is simply obtained by a free deceleration test under no air flow conditions, which can be easily produced by suddenly closing the inlet port.