A flow model is presented that predicts the swirl and turbulent velocities in an open chamber, cup-in-piston I.C. engine. The swirl model is based on an integral formulation of the angular momentum equation solved with an assumed tangential velocity profile form, Vθ(r). This enables the swirl model to predict a non-solid body rotation which is a function of the inlet flow, wall shear and squish motion during the engine cycle.The mean flow model is coupled with a global K-ε model which together predict shear stresses, mixing rates and heat transfer coefficients. An integrated form of the K-ε turbulence model is used which includes the compressibility, shear and boundary layer effects. Turbulence generated by the inlet flow is included and assumed to be proportional to the velocity past the intake valve. Also, the production of turbulence due to the boundary layer effects are included.The resulting model is compared with experimental data over a range of engine intake port and combustion chamber configurations. For the cup-in-piston geometry, an extensive study is made of the swirl level as a function of piston cup dimensions and compared with available data. Comparison of the total in-cylinder angular momentum, tangential velocity profiles and turbulence with experimental measurements show that the present model is superior to the standard solid-body rotation model.