A tractable model for in-cylinder fluid motion during the intake stroke is developed with particular attention given to fluid flow through the intake ports. Due to innovations in valve timing strategies for the 4-stroke internal combustion engine, the fluid flow effects of different valve timings must be quantified. An asynchronous valve timing strategy for Homogeneous Charge Compression Ignition engines serves as the motivation for this model development. For the purposes of real-time engine control, the model is not a multi-zone CFD model. Rather, the model divides the cylinder into two zones- a mixed zone and an unmixed zone. The flow is modeled as an intake jet of fluid that determines the rate at which hot exhaust gas is transferred from the unmixed to the mixed zone. The size of the mixed zone at the end of the intake process determines how well the cylinder contents are mixed. The effects of the valve timings on the flow velocity through each intake valve, cylinder pressure, and temperature are also presented.