The paper presents experimental results which point out to significant changes of the intake manifold air temperature during fast tip-in/tip-out engine transients. An adequate two-state polytropic manifold model is developed and experimentally validated. An emphasis is on the derivation and parameterization of an appropriate time-variant structure of the heat transfer coefficient. The polytropic manifold model is extended to a three-state form for the more general case of different heat transfer properties for the manifold plenum and runners. An influence of the engine back flow on the runner thermal transients is observed. A simple extension of the three-state model with the back flow effect is proposed.