The Chrysler 300C has offered various engine sizes throughout its production years. There's no single answer. To know the engine size of a *specific* Chrysler 300C, you need to know the model year.
The engines have ranged from V6s to V8s, with displacements typically between 3.6L and 6.1L (and even a 6.4L Hemi in some SRT8 models).