The paper presents a comparison of selected functions used in the description of the flow characteristics of a throttle body. The purpose of the performed analysis was to select functions that would represent the throttle flow capacity with the smallest possible error. Such characteristics are used in the modeling of the engine op-eration and very often influence the final effect of the mixture composition by e.g. setting a stoichiometric mixture. If, at a set throttle angle the stream of air mass is erratically defined then at the set fuel mass we shall receive an improper exhaust composition, which in modern engine designs is decisive in terms of proper engine operation. Indeed, in a real engine, the ECU based on the oxygen sensor feedback will adjust the fuel mass, but it is far better to double check the process of mixture formation rather than correct the consequences of its improper formation.