ABSTRACTA simple capillary ram food extruder was designed, constructed and mathematically modeled. The mathematical model was developed from a group of meaningful dimensionless parameters derived from a dimensional analysis of the extruder. This approach to modeling greatly reduced the number of experiments required to determine the model equation constants.Commercial defatted soy flour was used to conduct tests for validating the model. Flour moisture content, die length and die diameter were varied with all other variables remaining constant. Pressure loss through the extruder was the measured variable.The mathematical model fit the observed data accurately. It is proposed that once all experimental constants are determined, the general model may be used to determine rheological and thermodynamic data for doughs during extrusion processes. These data may then be used to develop certain rheological material functions.