The acoustic phenomena which take place inside an intake system greatly influence the volumetric efficiency of an engine. This paper deals with the problem of improving the volumetric efficiency of a single cylinder engine for a wide range of frequencies. The proposed solution is the addition of tunable resonators to the intake system. The variation of resonator tuning makes it possible to exploit the acoustic vibrations for a wide range of piston frequencies in the best way. Several intake systems equipped with resonators are studied using analytical methods. The best results are obtained when an in-series resonator with a variable volume is placed near the cylinder and when a side-branch resonator with a variable cross section is connected to a constant volume resonator. Several results are presented which deal with the behavior of the intake system during the induction stroke and which show the effectiveness of tunable resonators.